xref: /linux/drivers/gpu/drm/display/drm_dp_mst_topology.c (revision 7cc9196675234d4de0e1e19b9da1a8b86ecfeedd)

/*
 * Copyright © 2014 Red Hat
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#include <linux/bitfield.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/iopoll.h>

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
#include <linux/stacktrace.h>
#include <linux/sort.h>
#include <linux/timekeeping.h>
#include <linux/math64.h>
#endif

#include <drm/display/drm_dp_mst_helper.h>
#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_drv.h>
#include <drm/drm_edid.h>
#include <drm/drm_fixed.h>
#include <drm/drm_print.h>
#include <drm/drm_probe_helper.h>

#include "drm_dp_helper_internal.h"
#include "drm_dp_mst_topology_internal.h"

/**
 * DOC: dp mst helper
 *
 * These functions contain parts of the DisplayPort 1.2a MultiStream Transport
 * protocol. The helpers contain a topology manager and bandwidth manager.
 * The helpers encapsulate the sending and received of sideband msgs.
 */
struct drm_dp_pending_up_req {
	struct drm_dp_sideband_msg_hdr hdr;
	struct drm_dp_sideband_msg_req_body msg;
	struct list_head next;
};

static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
				  char *buf);

static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);

static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
				     int id, u8 start_slot, u8 num_slots);

static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_port *port,
				 int offset, int size, u8 *bytes);
static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
				  struct drm_dp_mst_port *port,
				  int offset, int size, u8 *bytes);

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
				    struct drm_dp_mst_branch *mstb);

static void
drm_dp_send_clear_payload_id_table(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_mst_branch *mstb);

static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
					   struct drm_dp_mst_branch *mstb,
					   struct drm_dp_mst_port *port);
static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
				 u8 *guid);

static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port);
static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port);
static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);

static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
						 struct drm_dp_mst_branch *branch);

#define DBG_PREFIX "[dp_mst]"

#define DP_STR(x) [DP_ ## x] = #x

static const char *drm_dp_mst_req_type_str(u8 req_type)
{
	static const char * const req_type_str[] = {
		DP_STR(GET_MSG_TRANSACTION_VERSION),
		DP_STR(LINK_ADDRESS),
		DP_STR(CONNECTION_STATUS_NOTIFY),
		DP_STR(ENUM_PATH_RESOURCES),
		DP_STR(ALLOCATE_PAYLOAD),
		DP_STR(QUERY_PAYLOAD),
		DP_STR(RESOURCE_STATUS_NOTIFY),
		DP_STR(CLEAR_PAYLOAD_ID_TABLE),
		DP_STR(REMOTE_DPCD_READ),
		DP_STR(REMOTE_DPCD_WRITE),
		DP_STR(REMOTE_I2C_READ),
		DP_STR(REMOTE_I2C_WRITE),
		DP_STR(POWER_UP_PHY),
		DP_STR(POWER_DOWN_PHY),
		DP_STR(SINK_EVENT_NOTIFY),
		DP_STR(QUERY_STREAM_ENC_STATUS),
	};

	if (req_type >= ARRAY_SIZE(req_type_str) ||
	    !req_type_str[req_type])
		return "unknown";

	return req_type_str[req_type];
}

#undef DP_STR
#define DP_STR(x) [DP_NAK_ ## x] = #x

static const char *drm_dp_mst_nak_reason_str(u8 nak_reason)
{
	static const char * const nak_reason_str[] = {
		DP_STR(WRITE_FAILURE),
		DP_STR(INVALID_READ),
		DP_STR(CRC_FAILURE),
		DP_STR(BAD_PARAM),
		DP_STR(DEFER),
		DP_STR(LINK_FAILURE),
		DP_STR(NO_RESOURCES),
		DP_STR(DPCD_FAIL),
		DP_STR(I2C_NAK),
		DP_STR(ALLOCATE_FAIL),
	};

	if (nak_reason >= ARRAY_SIZE(nak_reason_str) ||
	    !nak_reason_str[nak_reason])
		return "unknown";

	return nak_reason_str[nak_reason];
}

#undef DP_STR
#define DP_STR(x) [DRM_DP_SIDEBAND_TX_ ## x] = #x

static const char *drm_dp_mst_sideband_tx_state_str(int state)
{
	static const char * const sideband_reason_str[] = {
		DP_STR(QUEUED),
		DP_STR(START_SEND),
		DP_STR(SENT),
		DP_STR(RX),
		DP_STR(TIMEOUT),
	};

	if (state >= ARRAY_SIZE(sideband_reason_str) ||
	    !sideband_reason_str[state])
		return "unknown";

	return sideband_reason_str[state];
}

static int
drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
{
	int i;
	u8 unpacked_rad[16];

	for (i = 0; i < lct; i++) {
		if (i % 2)
			unpacked_rad[i] = rad[i / 2] >> 4;
		else
			unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
	}

	/* TODO: Eventually add something to printk so we can format the rad
	 * like this: 1.2.3
	 */
	return snprintf(out, len, "%*phC", lct, unpacked_rad);
}

/* sideband msg handling */
static u8 drm_dp_msg_header_crc4(const uint8_t *data, size_t num_nibbles)
{
	u8 bitmask = 0x80;
	u8 bitshift = 7;
	u8 array_index = 0;
	int number_of_bits = num_nibbles * 4;
	u8 remainder = 0;

	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		remainder |= (data[array_index] & bitmask) >> bitshift;
		bitmask >>= 1;
		bitshift--;
		if (bitmask == 0) {
			bitmask = 0x80;
			bitshift = 7;
			array_index++;
		}
		if ((remainder & 0x10) == 0x10)
			remainder ^= 0x13;
	}

	number_of_bits = 4;
	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		if ((remainder & 0x10) != 0)
			remainder ^= 0x13;
	}

	return remainder;
}

static u8 drm_dp_msg_data_crc4(const uint8_t *data, u8 number_of_bytes)
{
	u8 bitmask = 0x80;
	u8 bitshift = 7;
	u8 array_index = 0;
	int number_of_bits = number_of_bytes * 8;
	u16 remainder = 0;

	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		remainder |= (data[array_index] & bitmask) >> bitshift;
		bitmask >>= 1;
		bitshift--;
		if (bitmask == 0) {
			bitmask = 0x80;
			bitshift = 7;
			array_index++;
		}
		if ((remainder & 0x100) == 0x100)
			remainder ^= 0xd5;
	}

	number_of_bits = 8;
	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		if ((remainder & 0x100) != 0)
			remainder ^= 0xd5;
	}

	return remainder & 0xff;
}
static inline u8 drm_dp_calc_sb_hdr_size(struct drm_dp_sideband_msg_hdr *hdr)
{
	u8 size = 3;

	size += (hdr->lct / 2);
	return size;
}

static void drm_dp_encode_sideband_msg_hdr(struct drm_dp_sideband_msg_hdr *hdr,
					   u8 *buf, int *len)
{
	int idx = 0;
	int i;
	u8 crc4;

	buf[idx++] = ((hdr->lct & 0xf) << 4) | (hdr->lcr & 0xf);
	for (i = 0; i < (hdr->lct / 2); i++)
		buf[idx++] = hdr->rad[i];
	buf[idx++] = (hdr->broadcast << 7) | (hdr->path_msg << 6) |
		(hdr->msg_len & 0x3f);
	buf[idx++] = (hdr->somt << 7) | (hdr->eomt << 6) | (hdr->seqno << 4);

	crc4 = drm_dp_msg_header_crc4(buf, (idx * 2) - 1);
	buf[idx - 1] |= (crc4 & 0xf);

	*len = idx;
}

static bool drm_dp_decode_sideband_msg_hdr(const struct drm_dp_mst_topology_mgr *mgr,
					   struct drm_dp_sideband_msg_hdr *hdr,
					   u8 *buf, int buflen, u8 *hdrlen)
{
	u8 crc4;
	u8 len;
	int i;
	u8 idx;

	if (buf[0] == 0)
		return false;
	len = 3;
	len += ((buf[0] & 0xf0) >> 4) / 2;
	if (len > buflen)
		return false;
	crc4 = drm_dp_msg_header_crc4(buf, (len * 2) - 1);

	if ((crc4 & 0xf) != (buf[len - 1] & 0xf)) {
		drm_dbg_kms(mgr->dev, "crc4 mismatch 0x%x 0x%x\n", crc4, buf[len - 1]);
		return false;
	}

	hdr->lct = (buf[0] & 0xf0) >> 4;
	hdr->lcr = (buf[0] & 0xf);
	idx = 1;
	for (i = 0; i < (hdr->lct / 2); i++)
		hdr->rad[i] = buf[idx++];
	hdr->broadcast = (buf[idx] >> 7) & 0x1;
	hdr->path_msg = (buf[idx] >> 6) & 0x1;
	hdr->msg_len = buf[idx] & 0x3f;
	idx++;
	hdr->somt = (buf[idx] >> 7) & 0x1;
	hdr->eomt = (buf[idx] >> 6) & 0x1;
	hdr->seqno = (buf[idx] >> 4) & 0x1;
	idx++;
	*hdrlen = idx;
	return true;
}

void
drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req,
			   struct drm_dp_sideband_msg_tx *raw)
{
	int idx = 0;
	int i;
	u8 *buf = raw->msg;

	buf[idx++] = req->req_type & 0x7f;

	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
		idx++;
		break;
	case DP_ALLOCATE_PAYLOAD:
		buf[idx] = (req->u.allocate_payload.port_number & 0xf) << 4 |
			(req->u.allocate_payload.number_sdp_streams & 0xf);
		idx++;
		buf[idx] = (req->u.allocate_payload.vcpi & 0x7f);
		idx++;
		buf[idx] = (req->u.allocate_payload.pbn >> 8);
		idx++;
		buf[idx] = (req->u.allocate_payload.pbn & 0xff);
		idx++;
		for (i = 0; i < req->u.allocate_payload.number_sdp_streams / 2; i++) {
			buf[idx] = ((req->u.allocate_payload.sdp_stream_sink[i * 2] & 0xf) << 4) |
				(req->u.allocate_payload.sdp_stream_sink[i * 2 + 1] & 0xf);
			idx++;
		}
		if (req->u.allocate_payload.number_sdp_streams & 1) {
			i = req->u.allocate_payload.number_sdp_streams - 1;
			buf[idx] = (req->u.allocate_payload.sdp_stream_sink[i] & 0xf) << 4;
			idx++;
		}
		break;
	case DP_QUERY_PAYLOAD:
		buf[idx] = (req->u.query_payload.port_number & 0xf) << 4;
		idx++;
		buf[idx] = (req->u.query_payload.vcpi & 0x7f);
		idx++;
		break;
	case DP_REMOTE_DPCD_READ:
		buf[idx] = (req->u.dpcd_read.port_number & 0xf) << 4;
		buf[idx] |= ((req->u.dpcd_read.dpcd_address & 0xf0000) >> 16) & 0xf;
		idx++;
		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff00) >> 8;
		idx++;
		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff);
		idx++;
		buf[idx] = (req->u.dpcd_read.num_bytes);
		idx++;
		break;

	case DP_REMOTE_DPCD_WRITE:
		buf[idx] = (req->u.dpcd_write.port_number & 0xf) << 4;
		buf[idx] |= ((req->u.dpcd_write.dpcd_address & 0xf0000) >> 16) & 0xf;
		idx++;
		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff00) >> 8;
		idx++;
		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff);
		idx++;
		buf[idx] = (req->u.dpcd_write.num_bytes);
		idx++;
		memcpy(&buf[idx], req->u.dpcd_write.bytes, req->u.dpcd_write.num_bytes);
		idx += req->u.dpcd_write.num_bytes;
		break;
	case DP_REMOTE_I2C_READ:
		buf[idx] = (req->u.i2c_read.port_number & 0xf) << 4;
		buf[idx] |= (req->u.i2c_read.num_transactions & 0x3);
		idx++;
		for (i = 0; i < (req->u.i2c_read.num_transactions & 0x3); i++) {
			buf[idx] = req->u.i2c_read.transactions[i].i2c_dev_id & 0x7f;
			idx++;
			buf[idx] = req->u.i2c_read.transactions[i].num_bytes;
			idx++;
			memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes);
			idx += req->u.i2c_read.transactions[i].num_bytes;

			buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
			buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
			idx++;
		}
		buf[idx] = (req->u.i2c_read.read_i2c_device_id) & 0x7f;
		idx++;
		buf[idx] = (req->u.i2c_read.num_bytes_read);
		idx++;
		break;

	case DP_REMOTE_I2C_WRITE:
		buf[idx] = (req->u.i2c_write.port_number & 0xf) << 4;
		idx++;
		buf[idx] = (req->u.i2c_write.write_i2c_device_id) & 0x7f;
		idx++;
		buf[idx] = (req->u.i2c_write.num_bytes);
		idx++;
		memcpy(&buf[idx], req->u.i2c_write.bytes, req->u.i2c_write.num_bytes);
		idx += req->u.i2c_write.num_bytes;
		break;
	case DP_QUERY_STREAM_ENC_STATUS: {
		const struct drm_dp_query_stream_enc_status *msg;

		msg = &req->u.enc_status;
		buf[idx] = msg->stream_id;
		idx++;
		memcpy(&buf[idx], msg->client_id, sizeof(msg->client_id));
		idx += sizeof(msg->client_id);
		buf[idx] = 0;
		buf[idx] |= FIELD_PREP(GENMASK(1, 0), msg->stream_event);
		buf[idx] |= msg->valid_stream_event ? BIT(2) : 0;
		buf[idx] |= FIELD_PREP(GENMASK(4, 3), msg->stream_behavior);
		buf[idx] |= msg->valid_stream_behavior ? BIT(5) : 0;
		idx++;
		}
		break;
	}
	raw->cur_len = idx;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_encode_sideband_req);

/* Decode a sideband request we've encoded, mainly used for debugging */
int
drm_dp_decode_sideband_req(const struct drm_dp_sideband_msg_tx *raw,
			   struct drm_dp_sideband_msg_req_body *req)
{
	const u8 *buf = raw->msg;
	int i, idx = 0;

	req->req_type = buf[idx++] & 0x7f;
	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		req->u.port_num.port_number = (buf[idx] >> 4) & 0xf;
		break;
	case DP_ALLOCATE_PAYLOAD:
		{
			struct drm_dp_allocate_payload *a =
				&req->u.allocate_payload;

			a->number_sdp_streams = buf[idx] & 0xf;
			a->port_number = (buf[idx] >> 4) & 0xf;

			WARN_ON(buf[++idx] & 0x80);
			a->vcpi = buf[idx] & 0x7f;

			a->pbn = buf[++idx] << 8;
			a->pbn |= buf[++idx];

			idx++;
			for (i = 0; i < a->number_sdp_streams; i++) {
				a->sdp_stream_sink[i] =
					(buf[idx + (i / 2)] >> ((i % 2) ? 0 : 4)) & 0xf;
			}
		}
		break;
	case DP_QUERY_PAYLOAD:
		req->u.query_payload.port_number = (buf[idx] >> 4) & 0xf;
		WARN_ON(buf[++idx] & 0x80);
		req->u.query_payload.vcpi = buf[idx] & 0x7f;
		break;
	case DP_REMOTE_DPCD_READ:
		{
			struct drm_dp_remote_dpcd_read *r = &req->u.dpcd_read;

			r->port_number = (buf[idx] >> 4) & 0xf;

			r->dpcd_address = (buf[idx] << 16) & 0xf0000;
			r->dpcd_address |= (buf[++idx] << 8) & 0xff00;
			r->dpcd_address |= buf[++idx] & 0xff;

			r->num_bytes = buf[++idx];
		}
		break;
	case DP_REMOTE_DPCD_WRITE:
		{
			struct drm_dp_remote_dpcd_write *w =
				&req->u.dpcd_write;

			w->port_number = (buf[idx] >> 4) & 0xf;

			w->dpcd_address = (buf[idx] << 16) & 0xf0000;
			w->dpcd_address |= (buf[++idx] << 8) & 0xff00;
			w->dpcd_address |= buf[++idx] & 0xff;

			w->num_bytes = buf[++idx];

			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
					   GFP_KERNEL);
			if (!w->bytes)
				return -ENOMEM;
		}
		break;
	case DP_REMOTE_I2C_READ:
		{
			struct drm_dp_remote_i2c_read *r = &req->u.i2c_read;
			struct drm_dp_remote_i2c_read_tx *tx;
			bool failed = false;

			r->num_transactions = buf[idx] & 0x3;
			r->port_number = (buf[idx] >> 4) & 0xf;
			for (i = 0; i < r->num_transactions; i++) {
				tx = &r->transactions[i];

				tx->i2c_dev_id = buf[++idx] & 0x7f;
				tx->num_bytes = buf[++idx];
				tx->bytes = kmemdup(&buf[++idx],
						    tx->num_bytes,
						    GFP_KERNEL);
				if (!tx->bytes) {
					failed = true;
					break;
				}
				idx += tx->num_bytes;
				tx->no_stop_bit = (buf[idx] >> 5) & 0x1;
				tx->i2c_transaction_delay = buf[idx] & 0xf;
			}

			if (failed) {
				for (i = 0; i < r->num_transactions; i++) {
					tx = &r->transactions[i];
					kfree(tx->bytes);
				}
				return -ENOMEM;
			}

			r->read_i2c_device_id = buf[++idx] & 0x7f;
			r->num_bytes_read = buf[++idx];
		}
		break;
	case DP_REMOTE_I2C_WRITE:
		{
			struct drm_dp_remote_i2c_write *w = &req->u.i2c_write;

			w->port_number = (buf[idx] >> 4) & 0xf;
			w->write_i2c_device_id = buf[++idx] & 0x7f;
			w->num_bytes = buf[++idx];
			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
					   GFP_KERNEL);
			if (!w->bytes)
				return -ENOMEM;
		}
		break;
	case DP_QUERY_STREAM_ENC_STATUS:
		req->u.enc_status.stream_id = buf[idx++];
		for (i = 0; i < sizeof(req->u.enc_status.client_id); i++)
			req->u.enc_status.client_id[i] = buf[idx++];

		req->u.enc_status.stream_event = FIELD_GET(GENMASK(1, 0),
							   buf[idx]);
		req->u.enc_status.valid_stream_event = FIELD_GET(BIT(2),
								 buf[idx]);
		req->u.enc_status.stream_behavior = FIELD_GET(GENMASK(4, 3),
							      buf[idx]);
		req->u.enc_status.valid_stream_behavior = FIELD_GET(BIT(5),
								    buf[idx]);
		break;
	}

	return 0;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_decode_sideband_req);

void
drm_dp_dump_sideband_msg_req_body(const struct drm_dp_sideband_msg_req_body *req,
				  int indent, struct drm_printer *printer)
{
	int i;

#define P(f, ...) drm_printf_indent(printer, indent, f, ##__VA_ARGS__)
	if (req->req_type == DP_LINK_ADDRESS) {
		/* No contents to print */
		P("type=%s\n", drm_dp_mst_req_type_str(req->req_type));
		return;
	}

	P("type=%s contents:\n", drm_dp_mst_req_type_str(req->req_type));
	indent++;

	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		P("port=%d\n", req->u.port_num.port_number);
		break;
	case DP_ALLOCATE_PAYLOAD:
		P("port=%d vcpi=%d pbn=%d sdp_streams=%d %*ph\n",
		  req->u.allocate_payload.port_number,
		  req->u.allocate_payload.vcpi, req->u.allocate_payload.pbn,
		  req->u.allocate_payload.number_sdp_streams,
		  req->u.allocate_payload.number_sdp_streams,
		  req->u.allocate_payload.sdp_stream_sink);
		break;
	case DP_QUERY_PAYLOAD:
		P("port=%d vcpi=%d\n",
		  req->u.query_payload.port_number,
		  req->u.query_payload.vcpi);
		break;
	case DP_REMOTE_DPCD_READ:
		P("port=%d dpcd_addr=%05x len=%d\n",
		  req->u.dpcd_read.port_number, req->u.dpcd_read.dpcd_address,
		  req->u.dpcd_read.num_bytes);
		break;
	case DP_REMOTE_DPCD_WRITE:
		P("port=%d addr=%05x len=%d: %*ph\n",
		  req->u.dpcd_write.port_number,
		  req->u.dpcd_write.dpcd_address,
		  req->u.dpcd_write.num_bytes, req->u.dpcd_write.num_bytes,
		  req->u.dpcd_write.bytes);
		break;
	case DP_REMOTE_I2C_READ:
		P("port=%d num_tx=%d id=%d size=%d:\n",
		  req->u.i2c_read.port_number,
		  req->u.i2c_read.num_transactions,
		  req->u.i2c_read.read_i2c_device_id,
		  req->u.i2c_read.num_bytes_read);

		indent++;
		for (i = 0; i < req->u.i2c_read.num_transactions; i++) {
			const struct drm_dp_remote_i2c_read_tx *rtx =
				&req->u.i2c_read.transactions[i];

			P("%d: id=%03d size=%03d no_stop_bit=%d tx_delay=%03d: %*ph\n",
			  i, rtx->i2c_dev_id, rtx->num_bytes,
			  rtx->no_stop_bit, rtx->i2c_transaction_delay,
			  rtx->num_bytes, rtx->bytes);
		}
		break;
	case DP_REMOTE_I2C_WRITE:
		P("port=%d id=%d size=%d: %*ph\n",
		  req->u.i2c_write.port_number,
		  req->u.i2c_write.write_i2c_device_id,
		  req->u.i2c_write.num_bytes, req->u.i2c_write.num_bytes,
		  req->u.i2c_write.bytes);
		break;
	case DP_QUERY_STREAM_ENC_STATUS:
		P("stream_id=%u client_id=%*ph stream_event=%x "
		  "valid_event=%d stream_behavior=%x valid_behavior=%d",
		  req->u.enc_status.stream_id,
		  (int)ARRAY_SIZE(req->u.enc_status.client_id),
		  req->u.enc_status.client_id, req->u.enc_status.stream_event,
		  req->u.enc_status.valid_stream_event,
		  req->u.enc_status.stream_behavior,
		  req->u.enc_status.valid_stream_behavior);
		break;
	default:
		P("???\n");
		break;
	}
#undef P
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_dump_sideband_msg_req_body);

static inline void
drm_dp_mst_dump_sideband_msg_tx(struct drm_printer *p,
				const struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_sideband_msg_req_body req;
	char buf[64];
	int ret;
	int i;

	drm_dp_mst_rad_to_str(txmsg->dst->rad, txmsg->dst->lct, buf,
			      sizeof(buf));
	drm_printf(p, "txmsg cur_offset=%x cur_len=%x seqno=%x state=%s path_msg=%d dst=%s\n",
		   txmsg->cur_offset, txmsg->cur_len, txmsg->seqno,
		   drm_dp_mst_sideband_tx_state_str(txmsg->state),
		   txmsg->path_msg, buf);

	ret = drm_dp_decode_sideband_req(txmsg, &req);
	if (ret) {
		drm_printf(p, "<failed to decode sideband req: %d>\n", ret);
		return;
	}
	drm_dp_dump_sideband_msg_req_body(&req, 1, p);

	switch (req.req_type) {
	case DP_REMOTE_DPCD_WRITE:
		kfree(req.u.dpcd_write.bytes);
		break;
	case DP_REMOTE_I2C_READ:
		for (i = 0; i < req.u.i2c_read.num_transactions; i++)
			kfree(req.u.i2c_read.transactions[i].bytes);
		break;
	case DP_REMOTE_I2C_WRITE:
		kfree(req.u.i2c_write.bytes);
		break;
	}
}

static void drm_dp_crc_sideband_chunk_req(u8 *msg, u8 len)
{
	u8 crc4;

	crc4 = drm_dp_msg_data_crc4(msg, len);
	msg[len] = crc4;
}

static void drm_dp_encode_sideband_reply(struct drm_dp_sideband_msg_reply_body *rep,
					 struct drm_dp_sideband_msg_tx *raw)
{
	int idx = 0;
	u8 *buf = raw->msg;

	buf[idx++] = (rep->reply_type & 0x1) << 7 | (rep->req_type & 0x7f);

	raw->cur_len = idx;
}

static int drm_dp_sideband_msg_set_header(struct drm_dp_sideband_msg_rx *msg,
					  struct drm_dp_sideband_msg_hdr *hdr,
					  u8 hdrlen)
{
	/*
	 * ignore out-of-order messages or messages that are part of a
	 * failed transaction
	 */
	if (!hdr->somt && !msg->have_somt)
		return false;

	/* get length contained in this portion */
	msg->curchunk_idx = 0;
	msg->curchunk_len = hdr->msg_len;
	msg->curchunk_hdrlen = hdrlen;

	/* we have already gotten an somt - don't bother parsing */
	if (hdr->somt && msg->have_somt)
		return false;

	if (hdr->somt) {
		memcpy(&msg->initial_hdr, hdr,
		       sizeof(struct drm_dp_sideband_msg_hdr));
		msg->have_somt = true;
	}
	if (hdr->eomt)
		msg->have_eomt = true;

	return true;
}

/* this adds a chunk of msg to the builder to get the final msg */
static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg,
					   u8 *replybuf, u8 replybuflen)
{
	u8 crc4;

	memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
	msg->curchunk_idx += replybuflen;

	if (msg->curchunk_idx >= msg->curchunk_len) {
		/* do CRC */
		crc4 = drm_dp_msg_data_crc4(msg->chunk, msg->curchunk_len - 1);
		if (crc4 != msg->chunk[msg->curchunk_len - 1])
			print_hex_dump(KERN_DEBUG, "wrong crc",
				       DUMP_PREFIX_NONE, 16, 1,
				       msg->chunk,  msg->curchunk_len, false);
		/* copy chunk into bigger msg */
		memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len - 1);
		msg->curlen += msg->curchunk_len - 1;
	}
	return true;
}

static bool drm_dp_sideband_parse_link_address(const struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_sideband_msg_rx *raw,
					       struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;
	int i;

	memcpy(repmsg->u.link_addr.guid, &raw->msg[idx], 16);
	idx += 16;
	repmsg->u.link_addr.nports = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	for (i = 0; i < repmsg->u.link_addr.nports; i++) {
		if (raw->msg[idx] & 0x80)
			repmsg->u.link_addr.ports[i].input_port = 1;

		repmsg->u.link_addr.ports[i].peer_device_type = (raw->msg[idx] >> 4) & 0x7;
		repmsg->u.link_addr.ports[i].port_number = (raw->msg[idx] & 0xf);

		idx++;
		if (idx > raw->curlen)
			goto fail_len;
		repmsg->u.link_addr.ports[i].mcs = (raw->msg[idx] >> 7) & 0x1;
		repmsg->u.link_addr.ports[i].ddps = (raw->msg[idx] >> 6) & 0x1;
		if (repmsg->u.link_addr.ports[i].input_port == 0)
			repmsg->u.link_addr.ports[i].legacy_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
		idx++;
		if (idx > raw->curlen)
			goto fail_len;
		if (repmsg->u.link_addr.ports[i].input_port == 0) {
			repmsg->u.link_addr.ports[i].dpcd_revision = (raw->msg[idx]);
			idx++;
			if (idx > raw->curlen)
				goto fail_len;
			memcpy(repmsg->u.link_addr.ports[i].peer_guid, &raw->msg[idx], 16);
			idx += 16;
			if (idx > raw->curlen)
				goto fail_len;
			repmsg->u.link_addr.ports[i].num_sdp_streams = (raw->msg[idx] >> 4) & 0xf;
			repmsg->u.link_addr.ports[i].num_sdp_stream_sinks = (raw->msg[idx] & 0xf);
			idx++;

		}
		if (idx > raw->curlen)
			goto fail_len;
	}

	return true;
fail_len:
	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx *raw,
						   struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_dpcd_read_ack.port_number = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx];
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(repmsg->u.remote_dpcd_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_dpcd_read_ack.num_bytes);
	return true;
fail_len:
	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_write(struct drm_dp_sideband_msg_rx *raw,
						      struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_dpcd_write_ack.port_number = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_i2c_read_ack(struct drm_dp_sideband_msg_rx *raw,
						      struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_i2c_read_ack.port_number = (raw->msg[idx] & 0xf);
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.remote_i2c_read_ack.num_bytes = raw->msg[idx];
	idx++;
	/* TODO check */
	memcpy(repmsg->u.remote_i2c_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_i2c_read_ack.num_bytes);
	return true;
fail_len:
	DRM_DEBUG_KMS("remote i2c reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_enum_path_resources_ack(struct drm_dp_sideband_msg_rx *raw,
							  struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf;
	repmsg->u.path_resources.fec_capable = raw->msg[idx] & 0x1;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.path_resources.full_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.path_resources.avail_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("enum resource parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_allocate_payload_ack(struct drm_dp_sideband_msg_rx *raw,
							  struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.allocate_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.allocate_payload.vcpi = raw->msg[idx];
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.allocate_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_query_payload_ack(struct drm_dp_sideband_msg_rx *raw,
						    struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.query_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.query_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_power_updown_phy_ack(struct drm_dp_sideband_msg_rx *raw,
						       struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.port_number.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen) {
		DRM_DEBUG_KMS("power up/down phy parse length fail %d %d\n",
			      idx, raw->curlen);
		return false;
	}
	return true;
}

static bool
drm_dp_sideband_parse_query_stream_enc_status(
				struct drm_dp_sideband_msg_rx *raw,
				struct drm_dp_sideband_msg_reply_body *repmsg)
{
	struct drm_dp_query_stream_enc_status_ack_reply *reply;

	reply = &repmsg->u.enc_status;

	reply->stream_id = raw->msg[3];

	reply->reply_signed = raw->msg[2] & BIT(0);

	/*
	 * NOTE: It's my impression from reading the spec that the below parsing
	 * is correct. However I noticed while testing with an HDCP 1.4 display
	 * through an HDCP 2.2 hub that only bit 3 was set. In that case, I
	 * would expect both bits to be set. So keep the parsing following the
	 * spec, but beware reality might not match the spec (at least for some
	 * configurations).
	 */
	reply->hdcp_1x_device_present = raw->msg[2] & BIT(4);
	reply->hdcp_2x_device_present = raw->msg[2] & BIT(3);

	reply->query_capable_device_present = raw->msg[2] & BIT(5);
	reply->legacy_device_present = raw->msg[2] & BIT(6);
	reply->unauthorizable_device_present = raw->msg[2] & BIT(7);

	reply->auth_completed = !!(raw->msg[1] & BIT(3));
	reply->encryption_enabled = !!(raw->msg[1] & BIT(4));
	reply->repeater_present = !!(raw->msg[1] & BIT(5));
	reply->state = (raw->msg[1] & GENMASK(7, 6)) >> 6;

	return true;
}

static bool drm_dp_sideband_parse_reply(const struct drm_dp_mst_topology_mgr *mgr,
					struct drm_dp_sideband_msg_rx *raw,
					struct drm_dp_sideband_msg_reply_body *msg)
{
	memset(msg, 0, sizeof(*msg));
	msg->reply_type = (raw->msg[0] & 0x80) >> 7;
	msg->req_type = (raw->msg[0] & 0x7f);

	if (msg->reply_type == DP_SIDEBAND_REPLY_NAK) {
		memcpy(msg->u.nak.guid, &raw->msg[1], 16);
		msg->u.nak.reason = raw->msg[17];
		msg->u.nak.nak_data = raw->msg[18];
		return false;
	}

	switch (msg->req_type) {
	case DP_LINK_ADDRESS:
		return drm_dp_sideband_parse_link_address(mgr, raw, msg);
	case DP_QUERY_PAYLOAD:
		return drm_dp_sideband_parse_query_payload_ack(raw, msg);
	case DP_REMOTE_DPCD_READ:
		return drm_dp_sideband_parse_remote_dpcd_read(raw, msg);
	case DP_REMOTE_DPCD_WRITE:
		return drm_dp_sideband_parse_remote_dpcd_write(raw, msg);
	case DP_REMOTE_I2C_READ:
		return drm_dp_sideband_parse_remote_i2c_read_ack(raw, msg);
	case DP_REMOTE_I2C_WRITE:
		return true; /* since there's nothing to parse */
	case DP_ENUM_PATH_RESOURCES:
		return drm_dp_sideband_parse_enum_path_resources_ack(raw, msg);
	case DP_ALLOCATE_PAYLOAD:
		return drm_dp_sideband_parse_allocate_payload_ack(raw, msg);
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		return drm_dp_sideband_parse_power_updown_phy_ack(raw, msg);
	case DP_CLEAR_PAYLOAD_ID_TABLE:
		return true; /* since there's nothing to parse */
	case DP_QUERY_STREAM_ENC_STATUS:
		return drm_dp_sideband_parse_query_stream_enc_status(raw, msg);
	default:
		drm_err(mgr->dev, "Got unknown reply 0x%02x (%s)\n",
			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
		return false;
	}
}

static bool
drm_dp_sideband_parse_connection_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_sideband_msg_rx *raw,
					       struct drm_dp_sideband_msg_req_body *msg)
{
	int idx = 1;

	msg->u.conn_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(msg->u.conn_stat.guid, &raw->msg[idx], 16);
	idx += 16;
	if (idx > raw->curlen)
		goto fail_len;

	msg->u.conn_stat.legacy_device_plug_status = (raw->msg[idx] >> 6) & 0x1;
	msg->u.conn_stat.displayport_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
	msg->u.conn_stat.message_capability_status = (raw->msg[idx] >> 4) & 0x1;
	msg->u.conn_stat.input_port = (raw->msg[idx] >> 3) & 0x1;
	msg->u.conn_stat.peer_device_type = (raw->msg[idx] & 0x7);
	idx++;
	return true;
fail_len:
	drm_dbg_kms(mgr->dev, "connection status reply parse length fail %d %d\n",
		    idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_resource_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
							 struct drm_dp_sideband_msg_rx *raw,
							 struct drm_dp_sideband_msg_req_body *msg)
{
	int idx = 1;

	msg->u.resource_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(msg->u.resource_stat.guid, &raw->msg[idx], 16);
	idx += 16;
	if (idx > raw->curlen)
		goto fail_len;

	msg->u.resource_stat.available_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
	idx++;
	return true;
fail_len:
	drm_dbg_kms(mgr->dev, "resource status reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_req(const struct drm_dp_mst_topology_mgr *mgr,
				      struct drm_dp_sideband_msg_rx *raw,
				      struct drm_dp_sideband_msg_req_body *msg)
{
	memset(msg, 0, sizeof(*msg));
	msg->req_type = (raw->msg[0] & 0x7f);

	switch (msg->req_type) {
	case DP_CONNECTION_STATUS_NOTIFY:
		return drm_dp_sideband_parse_connection_status_notify(mgr, raw, msg);
	case DP_RESOURCE_STATUS_NOTIFY:
		return drm_dp_sideband_parse_resource_status_notify(mgr, raw, msg);
	default:
		drm_err(mgr->dev, "Got unknown request 0x%02x (%s)\n",
			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
		return false;
	}
}

static void build_dpcd_write(struct drm_dp_sideband_msg_tx *msg,
			     u8 port_num, u32 offset, u8 num_bytes, u8 *bytes)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_REMOTE_DPCD_WRITE;
	req.u.dpcd_write.port_number = port_num;
	req.u.dpcd_write.dpcd_address = offset;
	req.u.dpcd_write.num_bytes = num_bytes;
	req.u.dpcd_write.bytes = bytes;
	drm_dp_encode_sideband_req(&req, msg);
}

static void build_link_address(struct drm_dp_sideband_msg_tx *msg)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_LINK_ADDRESS;
	drm_dp_encode_sideband_req(&req, msg);
}

static void build_clear_payload_id_table(struct drm_dp_sideband_msg_tx *msg)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_CLEAR_PAYLOAD_ID_TABLE;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static int build_enum_path_resources(struct drm_dp_sideband_msg_tx *msg,
				     int port_num)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_ENUM_PATH_RESOURCES;
	req.u.port_num.port_number = port_num;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
	return 0;
}

static void build_allocate_payload(struct drm_dp_sideband_msg_tx *msg,
				   int port_num,
				   u8 vcpi, uint16_t pbn,
				   u8 number_sdp_streams,
				   u8 *sdp_stream_sink)
{
	struct drm_dp_sideband_msg_req_body req;

	memset(&req, 0, sizeof(req));
	req.req_type = DP_ALLOCATE_PAYLOAD;
	req.u.allocate_payload.port_number = port_num;
	req.u.allocate_payload.vcpi = vcpi;
	req.u.allocate_payload.pbn = pbn;
	req.u.allocate_payload.number_sdp_streams = number_sdp_streams;
	memcpy(req.u.allocate_payload.sdp_stream_sink, sdp_stream_sink,
		   number_sdp_streams);
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static void build_power_updown_phy(struct drm_dp_sideband_msg_tx *msg,
				   int port_num, bool power_up)
{
	struct drm_dp_sideband_msg_req_body req;

	if (power_up)
		req.req_type = DP_POWER_UP_PHY;
	else
		req.req_type = DP_POWER_DOWN_PHY;

	req.u.port_num.port_number = port_num;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static int
build_query_stream_enc_status(struct drm_dp_sideband_msg_tx *msg, u8 stream_id,
			      u8 *q_id)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_QUERY_STREAM_ENC_STATUS;
	req.u.enc_status.stream_id = stream_id;
	memcpy(req.u.enc_status.client_id, q_id,
	       sizeof(req.u.enc_status.client_id));
	req.u.enc_status.stream_event = 0;
	req.u.enc_status.valid_stream_event = false;
	req.u.enc_status.stream_behavior = 0;
	req.u.enc_status.valid_stream_behavior = false;

	drm_dp_encode_sideband_req(&req, msg);
	return 0;
}

static bool check_txmsg_state(struct drm_dp_mst_topology_mgr *mgr,
			      struct drm_dp_sideband_msg_tx *txmsg)
{
	unsigned int state;

	/*
	 * All updates to txmsg->state are protected by mgr->qlock, and the two
	 * cases we check here are terminal states. For those the barriers
	 * provided by the wake_up/wait_event pair are enough.
	 */
	state = READ_ONCE(txmsg->state);
	return (state == DRM_DP_SIDEBAND_TX_RX ||
		state == DRM_DP_SIDEBAND_TX_TIMEOUT);
}

static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
				    struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	unsigned long wait_timeout = msecs_to_jiffies(4000);
	unsigned long wait_expires = jiffies + wait_timeout;
	int ret;

	for (;;) {
		/*
		 * If the driver provides a way for this, change to
		 * poll-waiting for the MST reply interrupt if we didn't receive
		 * it for 50 msec. This would cater for cases where the HPD
		 * pulse signal got lost somewhere, even though the sink raised
		 * the corresponding MST interrupt correctly. One example is the
		 * Club 3D CAC-1557 TypeC -> DP adapter which for some reason
		 * filters out short pulses with a duration less than ~540 usec.
		 *
		 * The poll period is 50 msec to avoid missing an interrupt
		 * after the sink has cleared it (after a 110msec timeout
		 * since it raised the interrupt).
		 */
		ret = wait_event_timeout(mgr->tx_waitq,
					 check_txmsg_state(mgr, txmsg),
					 mgr->cbs->poll_hpd_irq ?
						msecs_to_jiffies(50) :
						wait_timeout);

		if (ret || !mgr->cbs->poll_hpd_irq ||
		    time_after(jiffies, wait_expires))
			break;

		mgr->cbs->poll_hpd_irq(mgr);
	}

	mutex_lock(&mgr->qlock);
	if (ret > 0) {
		if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
			ret = -EIO;
			goto out;
		}
	} else {
		drm_dbg_kms(mgr->dev, "timedout msg send %p %d %d\n",
			    txmsg, txmsg->state, txmsg->seqno);

		/* dump some state */
		ret = -EIO;

		/* remove from q */
		if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED ||
		    txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
		    txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
			list_del(&txmsg->next);
	}
out:
	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
		struct drm_printer p = drm_dbg_printer(mgr->dev, DRM_UT_DP,
						       DBG_PREFIX);

		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
	}
	mutex_unlock(&mgr->qlock);

	drm_dp_mst_kick_tx(mgr);
	return ret;
}

static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
{
	struct drm_dp_mst_branch *mstb;

	mstb = kzalloc(sizeof(*mstb), GFP_KERNEL);
	if (!mstb)
		return NULL;

	mstb->lct = lct;
	if (lct > 1)
		memcpy(mstb->rad, rad, lct / 2);
	INIT_LIST_HEAD(&mstb->ports);
	kref_init(&mstb->topology_kref);
	kref_init(&mstb->malloc_kref);
	return mstb;
}

static void drm_dp_free_mst_branch_device(struct kref *kref)
{
	struct drm_dp_mst_branch *mstb =
		container_of(kref, struct drm_dp_mst_branch, malloc_kref);

	if (mstb->port_parent)
		drm_dp_mst_put_port_malloc(mstb->port_parent);

	kfree(mstb);
}

/**
 * DOC: Branch device and port refcounting
 *
 * Topology refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * The refcounting schemes for &struct drm_dp_mst_branch and &struct
 * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
 * two different kinds of refcounts: topology refcounts, and malloc refcounts.
 *
 * Topology refcounts are not exposed to drivers, and are handled internally
 * by the DP MST helpers. The helpers use them in order to prevent the
 * in-memory topology state from being changed in the middle of critical
 * operations like changing the internal state of payload allocations. This
 * means each branch and port will be considered to be connected to the rest
 * of the topology until its topology refcount reaches zero. Additionally,
 * for ports this means that their associated &struct drm_connector will stay
 * registered with userspace until the port's refcount reaches 0.
 *
 * Malloc refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
 * drm_dp_mst_branch allocated even after all of its topology references have
 * been dropped, so that the driver or MST helpers can safely access each
 * branch's last known state before it was disconnected from the topology.
 * When the malloc refcount of a port or branch reaches 0, the memory
 * allocation containing the &struct drm_dp_mst_branch or &struct
 * drm_dp_mst_port respectively will be freed.
 *
 * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
 * to drivers. As of writing this documentation, there are no drivers that
 * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
 * helpers. Exposing this API to drivers in a race-free manner would take more
 * tweaking of the refcounting scheme, however patches are welcome provided
 * there is a legitimate driver usecase for this.
 *
 * Refcount relationships in a topology
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Let's take a look at why the relationship between topology and malloc
 * refcounts is designed the way it is.
 *
 * .. kernel-figure:: dp-mst/topology-figure-1.dot
 *
 *    An example of topology and malloc refs in a DP MST topology with two
 *    active payloads. Topology refcount increments are indicated by solid
 *    lines, and malloc refcount increments are indicated by dashed lines.
 *    Each starts from the branch which incremented the refcount, and ends at
 *    the branch to which the refcount belongs to, i.e. the arrow points the
 *    same way as the C pointers used to reference a structure.
 *
 * As you can see in the above figure, every branch increments the topology
 * refcount of its children, and increments the malloc refcount of its
 * parent. Additionally, every payload increments the malloc refcount of its
 * assigned port by 1.
 *
 * So, what would happen if MSTB #3 from the above figure was unplugged from
 * the system, but the driver hadn't yet removed payload #2 from port #3? The
 * topology would start to look like the figure below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-2.dot
 *
 *    Ports and branch devices which have been released from memory are
 *    colored grey, and references which have been removed are colored red.
 *
 * Whenever a port or branch device's topology refcount reaches zero, it will
 * decrement the topology refcounts of all its children, the malloc refcount
 * of its parent, and finally its own malloc refcount. For MSTB #4 and port
 * #4, this means they both have been disconnected from the topology and freed
 * from memory. But, because payload #2 is still holding a reference to port
 * #3, port #3 is removed from the topology but its &struct drm_dp_mst_port
 * is still accessible from memory. This also means port #3 has not yet
 * decremented the malloc refcount of MSTB #3, so its &struct
 * drm_dp_mst_branch will also stay allocated in memory until port #3's
 * malloc refcount reaches 0.
 *
 * This relationship is necessary because in order to release payload #2, we
 * need to be able to figure out the last relative of port #3 that's still
 * connected to the topology. In this case, we would travel up the topology as
 * shown below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-3.dot
 *
 * And finally, remove payload #2 by communicating with port #2 through
 * sideband transactions.
 */

/**
 * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_put_mstb_malloc()
 */
static void
drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
	kref_get(&mstb->malloc_kref);
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
}

/**
 * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_get_mstb_malloc()
 */
static void
drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
	kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
}

static void drm_dp_free_mst_port(struct kref *kref)
{
	struct drm_dp_mst_port *port =
		container_of(kref, struct drm_dp_mst_port, malloc_kref);

	drm_dp_mst_put_mstb_malloc(port->parent);
	kfree(port);
}

/**
 * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * Because @port could potentially be freed at any time by the DP MST helpers
 * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
 * function, drivers that which to make use of &struct drm_dp_mst_port should
 * ensure that they grab at least one main malloc reference to their MST ports
 * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
 * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
 *
 * See also: drm_dp_mst_put_port_malloc()
 */
void
drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
{
	kref_get(&port->malloc_kref);
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref));
}
EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);

/**
 * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * See also: drm_dp_mst_get_port_malloc()
 */
void
drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
{
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
	kref_put(&port->malloc_kref, drm_dp_free_mst_port);
}
EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)

#define STACK_DEPTH 8

static noinline void
__topology_ref_save(struct drm_dp_mst_topology_mgr *mgr,
		    struct drm_dp_mst_topology_ref_history *history,
		    enum drm_dp_mst_topology_ref_type type)
{
	struct drm_dp_mst_topology_ref_entry *entry = NULL;
	depot_stack_handle_t backtrace;
	ulong stack_entries[STACK_DEPTH];
	uint n;
	int i;

	n = stack_trace_save(stack_entries, ARRAY_SIZE(stack_entries), 1);
	backtrace = stack_depot_save(stack_entries, n, GFP_KERNEL);
	if (!backtrace)
		return;

	/* Try to find an existing entry for this backtrace */
	for (i = 0; i < history->len; i++) {
		if (history->entries[i].backtrace == backtrace) {
			entry = &history->entries[i];
			break;
		}
	}

	/* Otherwise add one */
	if (!entry) {
		struct drm_dp_mst_topology_ref_entry *new;
		int new_len = history->len + 1;

		new = krealloc(history->entries, sizeof(*new) * new_len,
			       GFP_KERNEL);
		if (!new)
			return;

		entry = &new[history->len];
		history->len = new_len;
		history->entries = new;

		entry->backtrace = backtrace;
		entry->type = type;
		entry->count = 0;
	}
	entry->count++;
	entry->ts_nsec = ktime_get_ns();
}

static int
topology_ref_history_cmp(const void *a, const void *b)
{
	const struct drm_dp_mst_topology_ref_entry *entry_a = a, *entry_b = b;

	if (entry_a->ts_nsec > entry_b->ts_nsec)
		return 1;
	else if (entry_a->ts_nsec < entry_b->ts_nsec)
		return -1;
	else
		return 0;
}

static inline const char *
topology_ref_type_to_str(enum drm_dp_mst_topology_ref_type type)
{
	if (type == DRM_DP_MST_TOPOLOGY_REF_GET)
		return "get";
	else
		return "put";
}

static void
__dump_topology_ref_history(struct drm_device *drm,
			    struct drm_dp_mst_topology_ref_history *history,
			    void *ptr, const char *type_str)
{
	struct drm_printer p = drm_dbg_printer(drm, DRM_UT_DP, DBG_PREFIX);
	char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
	int i;

	if (!buf)
		return;

	if (!history->len)
		goto out;

	/* First, sort the list so that it goes from oldest to newest
	 * reference entry
	 */
	sort(history->entries, history->len, sizeof(*history->entries),
	     topology_ref_history_cmp, NULL);

	drm_printf(&p, "%s (%p) topology count reached 0, dumping history:\n",
		   type_str, ptr);

	for (i = 0; i < history->len; i++) {
		const struct drm_dp_mst_topology_ref_entry *entry =
			&history->entries[i];
		u64 ts_nsec = entry->ts_nsec;
		u32 rem_nsec = do_div(ts_nsec, 1000000000);

		stack_depot_snprint(entry->backtrace, buf, PAGE_SIZE, 4);

		drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
			   entry->count,
			   topology_ref_type_to_str(entry->type),
			   ts_nsec, rem_nsec / 1000, buf);
	}

	/* Now free the history, since this is the only time we expose it */
	kfree(history->entries);
out:
	kfree(buf);
}

static __always_inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb)
{
	__dump_topology_ref_history(mstb->mgr->dev, &mstb->topology_ref_history,
				    mstb, "MSTB");
}

static __always_inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port)
{
	__dump_topology_ref_history(port->mgr->dev, &port->topology_ref_history,
				    port, "Port");
}

static __always_inline void
save_mstb_topology_ref(struct drm_dp_mst_branch *mstb,
		       enum drm_dp_mst_topology_ref_type type)
{
	__topology_ref_save(mstb->mgr, &mstb->topology_ref_history, type);
}

static __always_inline void
save_port_topology_ref(struct drm_dp_mst_port *port,
		       enum drm_dp_mst_topology_ref_type type)
{
	__topology_ref_save(port->mgr, &port->topology_ref_history, type);
}

static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr)
{
	mutex_lock(&mgr->topology_ref_history_lock);
}

static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr)
{
	mutex_unlock(&mgr->topology_ref_history_lock);
}
#else
static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb) {}
static inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port) {}
#define save_mstb_topology_ref(mstb, type)
#define save_port_topology_ref(port, type)
#endif

struct drm_dp_mst_atomic_payload *
drm_atomic_get_mst_payload_state(struct drm_dp_mst_topology_state *state,
				 struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_atomic_payload *payload;

	list_for_each_entry(payload, &state->payloads, next)
		if (payload->port == port)
			return payload;

	return NULL;
}
EXPORT_SYMBOL(drm_atomic_get_mst_payload_state);

static void drm_dp_destroy_mst_branch_device(struct kref *kref)
{
	struct drm_dp_mst_branch *mstb =
		container_of(kref, struct drm_dp_mst_branch, topology_kref);
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;

	drm_dp_mst_dump_mstb_topology_history(mstb);

	INIT_LIST_HEAD(&mstb->destroy_next);

	/*
	 * This can get called under mgr->mutex, so we need to perform the
	 * actual destruction of the mstb in another worker
	 */
	mutex_lock(&mgr->delayed_destroy_lock);
	list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list);
	mutex_unlock(&mgr->delayed_destroy_lock);
	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
 * branch device unless it's zero
 * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @mstb, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
 * reached 0). Holding a topology reference implies that a malloc reference
 * will be held to @mstb as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @mstb. If you already have a topology reference to @mstb, you
 * should use drm_dp_mst_topology_get_mstb() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
{
	int ret;

	topology_ref_history_lock(mstb->mgr);
	ret = kref_get_unless_zero(&mstb->topology_kref);
	if (ret) {
		drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
		save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
	}

	topology_ref_history_unlock(mstb->mgr);

	return ret;
}

/**
 * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
 * branch device
 * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 */
static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
{
	topology_ref_history_lock(mstb->mgr);

	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
	WARN_ON(kref_read(&mstb->topology_kref) == 0);
	kref_get(&mstb->topology_kref);
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));

	topology_ref_history_unlock(mstb->mgr);
}

/**
 * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
 *
 * Releases a topology reference from @mstb by decrementing
 * &drm_dp_mst_branch.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_get_mstb()
 */
static void
drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
{
	topology_ref_history_lock(mstb->mgr);

	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref) - 1);
	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_PUT);

	topology_ref_history_unlock(mstb->mgr);
	kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
}

static void drm_dp_destroy_port(struct kref *kref)
{
	struct drm_dp_mst_port *port =
		container_of(kref, struct drm_dp_mst_port, topology_kref);
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;

	drm_dp_mst_dump_port_topology_history(port);

	/* There's nothing that needs locking to destroy an input port yet */
	if (port->input) {
		drm_dp_mst_put_port_malloc(port);
		return;
	}

	drm_edid_free(port->cached_edid);

	/*
	 * we can't destroy the connector here, as we might be holding the
	 * mode_config.mutex from an EDID retrieval
	 */
	mutex_lock(&mgr->delayed_destroy_lock);
	list_add(&port->next, &mgr->destroy_port_list);
	mutex_unlock(&mgr->delayed_destroy_lock);
	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
 * port unless it's zero
 * @port: &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @port, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
 * 0). Holding a topology reference implies that a malloc reference will be
 * held to @port as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @port. If you already have a topology reference to @port, you
 * should use drm_dp_mst_topology_get_port() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_port()
 * drm_dp_mst_topology_put_port()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
{
	int ret;

	topology_ref_history_lock(port->mgr);
	ret = kref_get_unless_zero(&port->topology_kref);
	if (ret) {
		drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
		save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);
	}

	topology_ref_history_unlock(port->mgr);
	return ret;
}

/**
 * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
 * @port: The &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Increments &drm_dp_mst_port.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_put_port()
 */
static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
{
	topology_ref_history_lock(port->mgr);

	WARN_ON(kref_read(&port->topology_kref) == 0);
	kref_get(&port->topology_kref);
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);

	topology_ref_history_unlock(port->mgr);
}

/**
 * drm_dp_mst_topology_put_port() - release a topology reference to a port
 * @port: The &struct drm_dp_mst_port to release the topology reference from
 *
 * Releases a topology reference from @port by decrementing
 * &drm_dp_mst_port.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_get_port()
 */
static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
{
	topology_ref_history_lock(port->mgr);

	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref) - 1);
	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_PUT);

	topology_ref_history_unlock(port->mgr);
	kref_put(&port->topology_kref, drm_dp_destroy_port);
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
					      struct drm_dp_mst_branch *to_find)
{
	struct drm_dp_mst_port *port;
	struct drm_dp_mst_branch *rmstb;

	if (to_find == mstb)
		return mstb;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port->mstb) {
			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
			    port->mstb, to_find);
			if (rmstb)
				return rmstb;
		}
	}
	return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
				       struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_branch *rmstb = NULL;

	mutex_lock(&mgr->lock);
	if (mgr->mst_primary) {
		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
		    mgr->mst_primary, mstb);

		if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
			rmstb = NULL;
	}
	mutex_unlock(&mgr->lock);
	return rmstb;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
					      struct drm_dp_mst_port *to_find)
{
	struct drm_dp_mst_port *port, *mport;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port == to_find)
			return port;

		if (port->mstb) {
			mport = drm_dp_mst_topology_get_port_validated_locked(
			    port->mstb, to_find);
			if (mport)
				return mport;
		}
	}
	return NULL;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
				       struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_port *rport = NULL;

	mutex_lock(&mgr->lock);
	if (mgr->mst_primary) {
		rport = drm_dp_mst_topology_get_port_validated_locked(
		    mgr->mst_primary, port);

		if (rport && !drm_dp_mst_topology_try_get_port(rport))
			rport = NULL;
	}
	mutex_unlock(&mgr->lock);
	return rport;
}

static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
{
	struct drm_dp_mst_port *port;
	int ret;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port->port_num == port_num) {
			ret = drm_dp_mst_topology_try_get_port(port);
			return ret ? port : NULL;
		}
	}

	return NULL;
}

/*
 * calculate a new RAD for this MST branch device
 * if parent has an LCT of 2 then it has 1 nibble of RAD,
 * if parent has an LCT of 3 then it has 2 nibbles of RAD,
 */
static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
				 u8 *rad)
{
	int parent_lct = port->parent->lct;
	int shift = 4;
	int idx = (parent_lct - 1) / 2;

	if (parent_lct > 1) {
		memcpy(rad, port->parent->rad, idx + 1);
		shift = (parent_lct % 2) ? 4 : 0;
	} else
		rad[0] = 0;

	rad[idx] |= port->port_num << shift;
	return parent_lct + 1;
}

static bool drm_dp_mst_is_end_device(u8 pdt, bool mcs)
{
	switch (pdt) {
	case DP_PEER_DEVICE_DP_LEGACY_CONV:
	case DP_PEER_DEVICE_SST_SINK:
		return true;
	case DP_PEER_DEVICE_MST_BRANCHING:
		/* For sst branch device */
		if (!mcs)
			return true;

		return false;
	}
	return true;
}

static int
drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
		    bool new_mcs)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	struct drm_dp_mst_branch *mstb;
	u8 rad[8], lct;
	int ret = 0;

	if (port->pdt == new_pdt && port->mcs == new_mcs)
		return 0;

	/* Teardown the old pdt, if there is one */
	if (port->pdt != DP_PEER_DEVICE_NONE) {
		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
			/*
			 * If the new PDT would also have an i2c bus,
			 * don't bother with reregistering it
			 */
			if (new_pdt != DP_PEER_DEVICE_NONE &&
			    drm_dp_mst_is_end_device(new_pdt, new_mcs)) {
				port->pdt = new_pdt;
				port->mcs = new_mcs;
				return 0;
			}

			/* remove i2c over sideband */
			drm_dp_mst_unregister_i2c_bus(port);
		} else {
			mutex_lock(&mgr->lock);
			drm_dp_mst_topology_put_mstb(port->mstb);
			port->mstb = NULL;
			mutex_unlock(&mgr->lock);
		}
	}

	port->pdt = new_pdt;
	port->mcs = new_mcs;

	if (port->pdt != DP_PEER_DEVICE_NONE) {
		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
			/* add i2c over sideband */
			ret = drm_dp_mst_register_i2c_bus(port);
		} else {
			lct = drm_dp_calculate_rad(port, rad);
			mstb = drm_dp_add_mst_branch_device(lct, rad);
			if (!mstb) {
				ret = -ENOMEM;
				drm_err(mgr->dev, "Failed to create MSTB for port %p", port);
				goto out;
			}

			mutex_lock(&mgr->lock);
			port->mstb = mstb;
			mstb->mgr = port->mgr;
			mstb->port_parent = port;

			/*
			 * Make sure this port's memory allocation stays
			 * around until its child MSTB releases it
			 */
			drm_dp_mst_get_port_malloc(port);
			mutex_unlock(&mgr->lock);

			/* And make sure we send a link address for this */
			ret = 1;
		}
	}

out:
	if (ret < 0)
		port->pdt = DP_PEER_DEVICE_NONE;
	return ret;
}

/**
 * drm_dp_mst_dpcd_read() - read a series of bytes from the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to read
 * @buffer: buffer to store the register values
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_read() does for local
 * devices via actual AUX CH.
 *
 * Return: Number of bytes read, or negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_read(struct drm_dp_aux *aux,
			     unsigned int offset, void *buffer, size_t size)
{
	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
						    aux);

	return drm_dp_send_dpcd_read(port->mgr, port,
				     offset, size, buffer);
}

/**
 * drm_dp_mst_dpcd_write() - write a series of bytes to the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to write
 * @buffer: buffer containing the values to write
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_write() does for local
 * devices via actual AUX CH.
 *
 * Return: number of bytes written on success, negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_write(struct drm_dp_aux *aux,
			      unsigned int offset, void *buffer, size_t size)
{
	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
						    aux);

	return drm_dp_send_dpcd_write(port->mgr, port,
				      offset, size, buffer);
}

static int drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8 *guid)
{
	int ret = 0;

	memcpy(mstb->guid, guid, 16);

	if (!drm_dp_validate_guid(mstb->mgr, mstb->guid)) {
		if (mstb->port_parent) {
			ret = drm_dp_send_dpcd_write(mstb->mgr,
						     mstb->port_parent,
						     DP_GUID, 16, mstb->guid);
		} else {
			ret = drm_dp_dpcd_write(mstb->mgr->aux,
						DP_GUID, mstb->guid, 16);
		}
	}

	if (ret < 16 && ret > 0)
		return -EPROTO;

	return ret == 16 ? 0 : ret;
}

static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb,
				int pnum,
				char *proppath,
				size_t proppath_size)
{
	int i;
	char temp[8];

	snprintf(proppath, proppath_size, "mst:%d", mstb->mgr->conn_base_id);
	for (i = 0; i < (mstb->lct - 1); i++) {
		int shift = (i % 2) ? 0 : 4;
		int port_num = (mstb->rad[i / 2] >> shift) & 0xf;

		snprintf(temp, sizeof(temp), "-%d", port_num);
		strlcat(proppath, temp, proppath_size);
	}
	snprintf(temp, sizeof(temp), "-%d", pnum);
	strlcat(proppath, temp, proppath_size);
}

/**
 * drm_dp_mst_connector_late_register() - Late MST connector registration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to register the remote aux device for this MST port. Drivers should
 * call this from their mst connector's late_register hook to enable MST aux
 * devices.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_dp_mst_connector_late_register(struct drm_connector *connector,
				       struct drm_dp_mst_port *port)
{
	drm_dbg_kms(port->mgr->dev, "registering %s remote bus for %s\n",
		    port->aux.name, connector->kdev->kobj.name);

	port->aux.dev = connector->kdev;
	return drm_dp_aux_register_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_late_register);

/**
 * drm_dp_mst_connector_early_unregister() - Early MST connector unregistration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to unregister the remote aux device for this MST port, registered by
 * drm_dp_mst_connector_late_register(). Drivers should call this from their mst
 * connector's early_unregister hook.
 */
void drm_dp_mst_connector_early_unregister(struct drm_connector *connector,
					   struct drm_dp_mst_port *port)
{
	drm_dbg_kms(port->mgr->dev, "unregistering %s remote bus for %s\n",
		    port->aux.name, connector->kdev->kobj.name);
	drm_dp_aux_unregister_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);

static void
drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
			      struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	char proppath[255];
	int ret;

	build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
	port->connector = mgr->cbs->add_connector(mgr, port, proppath);
	if (!port->connector) {
		ret = -ENOMEM;
		goto error;
	}

	if (port->pdt != DP_PEER_DEVICE_NONE &&
	    drm_dp_mst_is_end_device(port->pdt, port->mcs) &&
	    port->port_num >= DP_MST_LOGICAL_PORT_0)
		port->cached_edid = drm_edid_read_ddc(port->connector,
						      &port->aux.ddc);

	drm_connector_register(port->connector);
	return;

error:
	drm_err(mgr->dev, "Failed to create connector for port %p: %d\n", port, ret);
}

/*
 * Drop a topology reference, and unlink the port from the in-memory topology
 * layout
 */
static void
drm_dp_mst_topology_unlink_port(struct drm_dp_mst_topology_mgr *mgr,
				struct drm_dp_mst_port *port)
{
	mutex_lock(&mgr->lock);
	port->parent->num_ports--;
	list_del(&port->next);
	mutex_unlock(&mgr->lock);
	drm_dp_mst_topology_put_port(port);
}

static struct drm_dp_mst_port *
drm_dp_mst_add_port(struct drm_device *dev,
		    struct drm_dp_mst_topology_mgr *mgr,
		    struct drm_dp_mst_branch *mstb, u8 port_number)
{
	struct drm_dp_mst_port *port = kzalloc(sizeof(*port), GFP_KERNEL);

	if (!port)
		return NULL;

	kref_init(&port->topology_kref);
	kref_init(&port->malloc_kref);
	port->parent = mstb;
	port->port_num = port_number;
	port->mgr = mgr;
	port->aux.name = "DPMST";
	port->aux.dev = dev->dev;
	port->aux.is_remote = true;

	/* initialize the MST downstream port's AUX crc work queue */
	port->aux.drm_dev = dev;
	drm_dp_remote_aux_init(&port->aux);

	/*
	 * Make sure the memory allocation for our parent branch stays
	 * around until our own memory allocation is released
	 */
	drm_dp_mst_get_mstb_malloc(mstb);

	return port;
}

static int
drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
				    struct drm_device *dev,
				    struct drm_dp_link_addr_reply_port *port_msg)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	struct drm_dp_mst_port *port;
	int old_ddps = 0, ret;
	u8 new_pdt = DP_PEER_DEVICE_NONE;
	bool new_mcs = 0;
	bool created = false, send_link_addr = false, changed = false;

	port = drm_dp_get_port(mstb, port_msg->port_number);
	if (!port) {
		port = drm_dp_mst_add_port(dev, mgr, mstb,
					   port_msg->port_number);
		if (!port)
			return -ENOMEM;
		created = true;
		changed = true;
	} else if (!port->input && port_msg->input_port && port->connector) {
		/* Since port->connector can't be changed here, we create a
		 * new port if input_port changes from 0 to 1
		 */
		drm_dp_mst_topology_unlink_port(mgr, port);
		drm_dp_mst_topology_put_port(port);
		port = drm_dp_mst_add_port(dev, mgr, mstb,
					   port_msg->port_number);
		if (!port)
			return -ENOMEM;
		changed = true;
		created = true;
	} else if (port->input && !port_msg->input_port) {
		changed = true;
	} else if (port->connector) {
		/* We're updating a port that's exposed to userspace, so do it
		 * under lock
		 */
		drm_modeset_lock(&mgr->base.lock, NULL);

		old_ddps = port->ddps;
		changed = port->ddps != port_msg->ddps ||
			(port->ddps &&
			 (port->ldps != port_msg->legacy_device_plug_status ||
			  port->dpcd_rev != port_msg->dpcd_revision ||
			  port->mcs != port_msg->mcs ||
			  port->pdt != port_msg->peer_device_type ||
			  port->num_sdp_stream_sinks !=
			  port_msg->num_sdp_stream_sinks));
	}

	port->input = port_msg->input_port;
	if (!port->input)
		new_pdt = port_msg->peer_device_type;
	new_mcs = port_msg->mcs;
	port->ddps = port_msg->ddps;
	port->ldps = port_msg->legacy_device_plug_status;
	port->dpcd_rev = port_msg->dpcd_revision;
	port->num_sdp_streams = port_msg->num_sdp_streams;
	port->num_sdp_stream_sinks = port_msg->num_sdp_stream_sinks;

	/* manage mstb port lists with mgr lock - take a reference
	   for this list */
	if (created) {
		mutex_lock(&mgr->lock);
		drm_dp_mst_topology_get_port(port);
		list_add(&port->next, &mstb->ports);
		mstb->num_ports++;
		mutex_unlock(&mgr->lock);
	}

	/*
	 * Reprobe PBN caps on both hotplug, and when re-probing the link
	 * for our parent mstb
	 */
	if (old_ddps != port->ddps || !created) {
		if (port->ddps && !port->input) {
			ret = drm_dp_send_enum_path_resources(mgr, mstb,
							      port);
			if (ret == 1)
				changed = true;
		} else {
			port->full_pbn = 0;
		}
	}

	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
	if (ret == 1) {
		send_link_addr = true;
	} else if (ret < 0) {
		drm_err(dev, "Failed to change PDT on port %p: %d\n", port, ret);
		goto fail;
	}

	/*
	 * If this port wasn't just created, then we're reprobing because
	 * we're coming out of suspend. In this case, always resend the link
	 * address if there's an MSTB on this port
	 */
	if (!created && port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
	    port->mcs)
		send_link_addr = true;

	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
	else if (!port->input)
		drm_dp_mst_port_add_connector(mstb, port);

	if (send_link_addr && port->mstb) {
		ret = drm_dp_send_link_address(mgr, port->mstb);
		if (ret == 1) /* MSTB below us changed */
			changed = true;
		else if (ret < 0)
			goto fail_put;
	}

	/* put reference to this port */
	drm_dp_mst_topology_put_port(port);
	return changed;

fail:
	drm_dp_mst_topology_unlink_port(mgr, port);
	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
fail_put:
	drm_dp_mst_topology_put_port(port);
	return ret;
}

static int
drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
			    struct drm_dp_connection_status_notify *conn_stat)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	struct drm_dp_mst_port *port;
	int old_ddps, ret;
	u8 new_pdt;
	bool new_mcs;
	bool dowork = false, create_connector = false;

	port = drm_dp_get_port(mstb, conn_stat->port_number);
	if (!port)
		return 0;

	if (port->connector) {
		if (!port->input && conn_stat->input_port) {
			/*
			 * We can't remove a connector from an already exposed
			 * port, so just throw the port out and make sure we
			 * reprobe the link address of it's parent MSTB
			 */
			drm_dp_mst_topology_unlink_port(mgr, port);
			mstb->link_address_sent = false;
			dowork = true;
			goto out;
		}

		/* Locking is only needed if the port's exposed to userspace */
		drm_modeset_lock(&mgr->base.lock, NULL);
	} else if (port->input && !conn_stat->input_port) {
		create_connector = true;
		/* Reprobe link address so we get num_sdp_streams */
		mstb->link_address_sent = false;
		dowork = true;
	}

	old_ddps = port->ddps;
	port->input = conn_stat->input_port;
	port->ldps = conn_stat->legacy_device_plug_status;
	port->ddps = conn_stat->displayport_device_plug_status;

	if (old_ddps != port->ddps) {
		if (port->ddps && !port->input)
			drm_dp_send_enum_path_resources(mgr, mstb, port);
		else
			port->full_pbn = 0;
	}

	new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
	new_mcs = conn_stat->message_capability_status;
	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
	if (ret == 1) {
		dowork = true;
	} else if (ret < 0) {
		drm_err(mgr->dev, "Failed to change PDT for port %p: %d\n", port, ret);
		dowork = false;
	}

	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
	else if (create_connector)
		drm_dp_mst_port_add_connector(mstb, port);

out:
	drm_dp_mst_topology_put_port(port);
	return dowork;
}

static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
							       u8 lct, u8 *rad)
{
	struct drm_dp_mst_branch *mstb;
	struct drm_dp_mst_port *port;
	int i, ret;
	/* find the port by iterating down */

	mutex_lock(&mgr->lock);
	mstb = mgr->mst_primary;

	if (!mstb)
		goto out;

	for (i = 0; i < lct - 1; i++) {
		int shift = (i % 2) ? 0 : 4;
		int port_num = (rad[i / 2] >> shift) & 0xf;

		list_for_each_entry(port, &mstb->ports, next) {
			if (port->port_num == port_num) {
				mstb = port->mstb;
				if (!mstb) {
					drm_err(mgr->dev,
						"failed to lookup MSTB with lct %d, rad %02x\n",
						lct, rad[0]);
					goto out;
				}

				break;
			}
		}
	}
	ret = drm_dp_mst_topology_try_get_mstb(mstb);
	if (!ret)
		mstb = NULL;
out:
	mutex_unlock(&mgr->lock);
	return mstb;
}

static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
	struct drm_dp_mst_branch *mstb,
	const uint8_t *guid)
{
	struct drm_dp_mst_branch *found_mstb;
	struct drm_dp_mst_port *port;

	if (!mstb)
		return NULL;

	if (memcmp(mstb->guid, guid, 16) == 0)
		return mstb;


	list_for_each_entry(port, &mstb->ports, next) {
		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);

		if (found_mstb)
			return found_mstb;
	}

	return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
				     const uint8_t *guid)
{
	struct drm_dp_mst_branch *mstb;
	int ret;

	/* find the port by iterating down */
	mutex_lock(&mgr->lock);

	mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
	if (mstb) {
		ret = drm_dp_mst_topology_try_get_mstb(mstb);
		if (!ret)
			mstb = NULL;
	}

	mutex_unlock(&mgr->lock);
	return mstb;
}

static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_port *port;
	int ret;
	bool changed = false;

	if (!mstb->link_address_sent) {
		ret = drm_dp_send_link_address(mgr, mstb);
		if (ret == 1)
			changed = true;
		else if (ret < 0)
			return ret;
	}

	list_for_each_entry(port, &mstb->ports, next) {
		if (port->input || !port->ddps || !port->mstb)
			continue;

		ret = drm_dp_check_and_send_link_address(mgr, port->mstb);
		if (ret == 1)
			changed = true;
		else if (ret < 0)
			return ret;
	}

	return changed;
}

static void drm_dp_mst_link_probe_work(struct work_struct *work)
{
	struct drm_dp_mst_topology_mgr *mgr =
		container_of(work, struct drm_dp_mst_topology_mgr, work);
	struct drm_device *dev = mgr->dev;
	struct drm_dp_mst_branch *mstb;
	int ret;
	bool clear_payload_id_table;

	mutex_lock(&mgr->probe_lock);

	mutex_lock(&mgr->lock);
	clear_payload_id_table = !mgr->payload_id_table_cleared;
	mgr->payload_id_table_cleared = true;

	mstb = mgr->mst_primary;
	if (mstb) {
		ret = drm_dp_mst_topology_try_get_mstb(mstb);
		if (!ret)
			mstb = NULL;
	}
	mutex_unlock(&mgr->lock);
	if (!mstb) {
		mutex_unlock(&mgr->probe_lock);
		return;
	}

	/*
	 * Certain branch devices seem to incorrectly report an available_pbn
	 * of 0 on downstream sinks, even after clearing the
	 * DP_PAYLOAD_ALLOCATE_* registers in
	 * drm_dp_mst_topology_mgr_set_mst(). Namely, the CableMatters USB-C
	 * 2x DP hub. Sending a CLEAR_PAYLOAD_ID_TABLE message seems to make
	 * things work again.
	 */
	if (clear_payload_id_table) {
		drm_dbg_kms(dev, "Clearing payload ID table\n");
		drm_dp_send_clear_payload_id_table(mgr, mstb);
	}

	ret = drm_dp_check_and_send_link_address(mgr, mstb);
	drm_dp_mst_topology_put_mstb(mstb);

	mutex_unlock(&mgr->probe_lock);
	if (ret > 0)
		drm_kms_helper_hotplug_event(dev);
}

static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
				 u8 *guid)
{
	u64 salt;

	if (memchr_inv(guid, 0, 16))
		return true;

	salt = get_jiffies_64();

	memcpy(&guid[0], &salt, sizeof(u64));
	memcpy(&guid[8], &salt, sizeof(u64));

	return false;
}

static void build_dpcd_read(struct drm_dp_sideband_msg_tx *msg,
			    u8 port_num, u32 offset, u8 num_bytes)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_REMOTE_DPCD_READ;
	req.u.dpcd_read.port_number = port_num;
	req.u.dpcd_read.dpcd_address = offset;
	req.u.dpcd_read.num_bytes = num_bytes;
	drm_dp_encode_sideband_req(&req, msg);
}

static int drm_dp_send_sideband_msg(struct drm_dp_mst_topology_mgr *mgr,
				    bool up, u8 *msg, int len)
{
	int ret;
	int regbase = up ? DP_SIDEBAND_MSG_UP_REP_BASE : DP_SIDEBAND_MSG_DOWN_REQ_BASE;
	int tosend, total, offset;
	int retries = 0;

retry:
	total = len;
	offset = 0;
	do {
		tosend = min3(mgr->max_dpcd_transaction_bytes, 16, total);

		ret = drm_dp_dpcd_write(mgr->aux, regbase + offset,
					&msg[offset],
					tosend);
		if (ret != tosend) {
			if (ret == -EIO && retries < 5) {
				retries++;
				goto retry;
			}
			drm_dbg_kms(mgr->dev, "failed to dpcd write %d %d\n", tosend, ret);

			return -EIO;
		}
		offset += tosend;
		total -= tosend;
	} while (total > 0);
	return 0;
}

static int set_hdr_from_dst_qlock(struct drm_dp_sideband_msg_hdr *hdr,
				  struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_mst_branch *mstb = txmsg->dst;
	u8 req_type;

	req_type = txmsg->msg[0] & 0x7f;
	if (req_type == DP_CONNECTION_STATUS_NOTIFY ||
		req_type == DP_RESOURCE_STATUS_NOTIFY ||
		req_type == DP_CLEAR_PAYLOAD_ID_TABLE)
		hdr->broadcast = 1;
	else
		hdr->broadcast = 0;
	hdr->path_msg = txmsg->path_msg;
	if (hdr->broadcast) {
		hdr->lct = 1;
		hdr->lcr = 6;
	} else {
		hdr->lct = mstb->lct;
		hdr->lcr = mstb->lct - 1;
	}

	memcpy(hdr->rad, mstb->rad, hdr->lct / 2);

	return 0;
}
/*
 * process a single block of the next message in the sideband queue
 */
static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_sideband_msg_tx *txmsg,
				   bool up)
{
	u8 chunk[48];
	struct drm_dp_sideband_msg_hdr hdr;
	int len, space, idx, tosend;
	int ret;

	if (txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
		return 0;

	memset(&hdr, 0, sizeof(struct drm_dp_sideband_msg_hdr));

	if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED)
		txmsg->state = DRM_DP_SIDEBAND_TX_START_SEND;

	/* make hdr from dst mst */
	ret = set_hdr_from_dst_qlock(&hdr, txmsg);
	if (ret < 0)
		return ret;

	/* amount left to send in this message */
	len = txmsg->cur_len - txmsg->cur_offset;

	/* 48 - sideband msg size - 1 byte for data CRC, x header bytes */
	space = 48 - 1 - drm_dp_calc_sb_hdr_size(&hdr);

	tosend = min(len, space);
	if (len == txmsg->cur_len)
		hdr.somt = 1;
	if (space >= len)
		hdr.eomt = 1;


	hdr.msg_len = tosend + 1;
	drm_dp_encode_sideband_msg_hdr(&hdr, chunk, &idx);
	memcpy(&chunk[idx], &txmsg->msg[txmsg->cur_offset], tosend);
	/* add crc at end */
	drm_dp_crc_sideband_chunk_req(&chunk[idx], tosend);
	idx += tosend + 1;

	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
	if (ret) {
		if (drm_debug_enabled(DRM_UT_DP)) {
			struct drm_printer p = drm_dbg_printer(mgr->dev,
							       DRM_UT_DP,
							       DBG_PREFIX);

			drm_printf(&p, "sideband msg failed to send\n");
			drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
		}
		return ret;
	}

	txmsg->cur_offset += tosend;
	if (txmsg->cur_offset == txmsg->cur_len) {
		txmsg->state = DRM_DP_SIDEBAND_TX_SENT;
		return 1;
	}
	return 0;
}

static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	int ret;

	WARN_ON(!mutex_is_locked(&mgr->qlock));

	/* construct a chunk from the first msg in the tx_msg queue */
	if (list_empty(&mgr->tx_msg_downq))
		return;

	txmsg = list_first_entry(&mgr->tx_msg_downq,
				 struct drm_dp_sideband_msg_tx, next);
	ret = process_single_tx_qlock(mgr, txmsg, false);
	if (ret < 0) {
		drm_dbg_kms(mgr->dev, "failed to send msg in q %d\n", ret);
		list_del(&txmsg->next);
		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
		wake_up_all(&mgr->tx_waitq);
	}
}

static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_sideband_msg_tx *txmsg)
{
	mutex_lock(&mgr->qlock);
	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);

	if (drm_debug_enabled(DRM_UT_DP)) {
		struct drm_printer p = drm_dbg_printer(mgr->dev, DRM_UT_DP,
						       DBG_PREFIX);

		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
	}

	if (list_is_singular(&mgr->tx_msg_downq))
		process_single_down_tx_qlock(mgr);
	mutex_unlock(&mgr->qlock);
}

static void
drm_dp_dump_link_address(const struct drm_dp_mst_topology_mgr *mgr,
			 struct drm_dp_link_address_ack_reply *reply)
{
	struct drm_dp_link_addr_reply_port *port_reply;
	int i;

	for (i = 0; i < reply->nports; i++) {
		port_reply = &reply->ports[i];
		drm_dbg_kms(mgr->dev,
			    "port %d: input %d, pdt: %d, pn: %d, dpcd_rev: %02x, mcs: %d, ddps: %d, ldps %d, sdp %d/%d\n",
			    i,
			    port_reply->input_port,
			    port_reply->peer_device_type,
			    port_reply->port_number,
			    port_reply->dpcd_revision,
			    port_reply->mcs,
			    port_reply->ddps,
			    port_reply->legacy_device_plug_status,
			    port_reply->num_sdp_streams,
			    port_reply->num_sdp_stream_sinks);
	}
}

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
				     struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_link_address_ack_reply *reply;
	struct drm_dp_mst_port *port, *tmp;
	int i, ret, port_mask = 0;
	bool changed = false;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg)
		return -ENOMEM;

	txmsg->dst = mstb;
	build_link_address(txmsg);

	mstb->link_address_sent = true;
	drm_dp_queue_down_tx(mgr, txmsg);

	/* FIXME: Actually do some real error handling here */
	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret <= 0) {
		drm_err(mgr->dev, "Sending link address failed with %d\n", ret);
		goto out;
	}
	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
		drm_err(mgr->dev, "link address NAK received\n");
		ret = -EIO;
		goto out;
	}

	reply = &txmsg->reply.u.link_addr;
	drm_dbg_kms(mgr->dev, "link address reply: %d\n", reply->nports);
	drm_dp_dump_link_address(mgr, reply);

	ret = drm_dp_check_mstb_guid(mstb, reply->guid);
	if (ret) {
		char buf[64];

		drm_dp_mst_rad_to_str(mstb->rad, mstb->lct, buf, sizeof(buf));
		drm_err(mgr->dev, "GUID check on %s failed: %d\n", buf, ret);
		goto out;
	}

	for (i = 0; i < reply->nports; i++) {
		port_mask |= BIT(reply->ports[i].port_number);
		ret = drm_dp_mst_handle_link_address_port(mstb, mgr->dev,
							  &reply->ports[i]);
		if (ret == 1)
			changed = true;
		else if (ret < 0)
			goto out;
	}

	/* Prune any ports that are currently a part of mstb in our in-memory
	 * topology, but were not seen in this link address. Usually this
	 * means that they were removed while the topology was out of sync,
	 * e.g. during suspend/resume
	 */
	mutex_lock(&mgr->lock);
	list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
		if (port_mask & BIT(port->port_num))
			continue;

		drm_dbg_kms(mgr->dev, "port %d was not in link address, removing\n",
			    port->port_num);
		list_del(&port->next);
		drm_dp_mst_topology_put_port(port);
		changed = true;
	}
	mutex_unlock(&mgr->lock);

out:
	if (ret <= 0)
		mstb->link_address_sent = false;
	kfree(txmsg);
	return ret < 0 ? ret : changed;
}

static void
drm_dp_send_clear_payload_id_table(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	int ret;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg)
		return;

	txmsg->dst = mstb;
	build_clear_payload_id_table(txmsg);

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret > 0 && txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
		drm_dbg_kms(mgr->dev, "clear payload table id nak received\n");

	kfree(txmsg);
}

static int
drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
				struct drm_dp_mst_branch *mstb,
				struct drm_dp_mst_port *port)
{
	struct drm_dp_enum_path_resources_ack_reply *path_res;
	struct drm_dp_sideband_msg_tx *txmsg;
	int ret;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg)
		return -ENOMEM;

	txmsg->dst = mstb;
	build_enum_path_resources(txmsg, port->port_num);

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret > 0) {
		ret = 0;
		path_res = &txmsg->reply.u.path_resources;

		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
			drm_dbg_kms(mgr->dev, "enum path resources nak received\n");
		} else {
			if (port->port_num != path_res->port_number)
				DRM_ERROR("got incorrect port in response\n");

			drm_dbg_kms(mgr->dev, "enum path resources %d: %d %d\n",
				    path_res->port_number,
				    path_res->full_payload_bw_number,
				    path_res->avail_payload_bw_number);

			/*
			 * If something changed, make sure we send a
			 * hotplug
			 */
			if (port->full_pbn != path_res->full_payload_bw_number ||
			    port->fec_capable != path_res->fec_capable)
				ret = 1;

			port->full_pbn = path_res->full_payload_bw_number;
			port->fec_capable = path_res->fec_capable;
		}
	}

	kfree(txmsg);
	return ret;
}

static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm_dp_mst_branch *mstb)
{
	if (!mstb->port_parent)
		return NULL;

	if (mstb->port_parent->mstb != mstb)
		return mstb->port_parent;

	return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
}

/*
 * Searches upwards in the topology starting from mstb to try to find the
 * closest available parent of mstb that's still connected to the rest of the
 * topology. This can be used in order to perform operations like releasing
 * payloads, where the branch device which owned the payload may no longer be
 * around and thus would require that the payload on the last living relative
 * be freed instead.
 */
static struct drm_dp_mst_branch *
drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
					struct drm_dp_mst_branch *mstb,
					int *port_num)
{
	struct drm_dp_mst_branch *rmstb = NULL;
	struct drm_dp_mst_port *found_port;

	mutex_lock(&mgr->lock);
	if (!mgr->mst_primary)
		goto out;

	do {
		found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
		if (!found_port)
			break;

		if (drm_dp_mst_topology_try_get_mstb(found_port->parent)) {
			rmstb = found_port->parent;
			*port_num = found_port->port_num;
		} else {
			/* Search again, starting from this parent */
			mstb = found_port->parent;
		}
	} while (!rmstb);
out:
	mutex_unlock(&mgr->lock);
	return rmstb;
}

static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_mst_port *port,
				   int id,
				   int pbn)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_mst_branch *mstb;
	int ret, port_num;
	u8 sinks[DRM_DP_MAX_SDP_STREAMS];
	int i;

	port_num = port->port_num;
	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
	if (!mstb) {
		mstb = drm_dp_get_last_connected_port_and_mstb(mgr,
							       port->parent,
							       &port_num);

		if (!mstb)
			return -EINVAL;
	}

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		ret = -ENOMEM;
		goto fail_put;
	}

	for (i = 0; i < port->num_sdp_streams; i++)
		sinks[i] = i;

	txmsg->dst = mstb;
	build_allocate_payload(txmsg, port_num,
			       id,
			       pbn, port->num_sdp_streams, sinks);

	drm_dp_queue_down_tx(mgr, txmsg);

	/*
	 * FIXME: there is a small chance that between getting the last
	 * connected mstb and sending the payload message, the last connected
	 * mstb could also be removed from the topology. In the future, this
	 * needs to be fixed by restarting the
	 * drm_dp_get_last_connected_port_and_mstb() search in the event of a
	 * timeout if the topology is still connected to the system.
	 */
	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret > 0) {
		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
			ret = -EINVAL;
		else
			ret = 0;
	}
	kfree(txmsg);
fail_put:
	drm_dp_mst_topology_put_mstb(mstb);
	return ret;
}

int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_port *port, bool power_up)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	int ret;

	port = drm_dp_mst_topology_get_port_validated(mgr, port);
	if (!port)
		return -EINVAL;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		drm_dp_mst_topology_put_port(port);
		return -ENOMEM;
	}

	txmsg->dst = port->parent;
	build_power_updown_phy(txmsg, port->port_num, power_up);
	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(port->parent, txmsg);
	if (ret > 0) {
		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
			ret = -EINVAL;
		else
			ret = 0;
	}
	kfree(txmsg);
	drm_dp_mst_topology_put_port(port);

	return ret;
}
EXPORT_SYMBOL(drm_dp_send_power_updown_phy);

int drm_dp_send_query_stream_enc_status(struct drm_dp_mst_topology_mgr *mgr,
		struct drm_dp_mst_port *port,
		struct drm_dp_query_stream_enc_status_ack_reply *status)
{
	struct drm_dp_mst_topology_state *state;
	struct drm_dp_mst_atomic_payload *payload;
	struct drm_dp_sideband_msg_tx *txmsg;
	u8 nonce[7];
	int ret;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg)
		return -ENOMEM;

	port = drm_dp_mst_topology_get_port_validated(mgr, port);
	if (!port) {
		ret = -EINVAL;
		goto out_get_port;
	}

	get_random_bytes(nonce, sizeof(nonce));

	drm_modeset_lock(&mgr->base.lock, NULL);
	state = to_drm_dp_mst_topology_state(mgr->base.state);
	payload = drm_atomic_get_mst_payload_state(state, port);

	/*
	 * "Source device targets the QUERY_STREAM_ENCRYPTION_STATUS message
	 *  transaction at the MST Branch device directly connected to the
	 *  Source"
	 */
	txmsg->dst = mgr->mst_primary;

	build_query_stream_enc_status(txmsg, payload->vcpi, nonce);

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mgr->mst_primary, txmsg);
	if (ret < 0) {
		goto out;
	} else if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
		drm_dbg_kms(mgr->dev, "query encryption status nak received\n");
		ret = -ENXIO;
		goto out;
	}

	ret = 0;
	memcpy(status, &txmsg->reply.u.enc_status, sizeof(*status));

out:
	drm_modeset_unlock(&mgr->base.lock);
	drm_dp_mst_topology_put_port(port);
out_get_port:
	kfree(txmsg);
	return ret;
}
EXPORT_SYMBOL(drm_dp_send_query_stream_enc_status);

static int drm_dp_create_payload_at_dfp(struct drm_dp_mst_topology_mgr *mgr,
					struct drm_dp_mst_atomic_payload *payload)
{
	return drm_dp_dpcd_write_payload(mgr, payload->vcpi, payload->vc_start_slot,
					 payload->time_slots);
}

static int drm_dp_create_payload_to_remote(struct drm_dp_mst_topology_mgr *mgr,
					   struct drm_dp_mst_atomic_payload *payload)
{
	int ret;
	struct drm_dp_mst_port *port = drm_dp_mst_topology_get_port_validated(mgr, payload->port);

	if (!port)
		return -EIO;

	ret = drm_dp_payload_send_msg(mgr, port, payload->vcpi, payload->pbn);
	drm_dp_mst_topology_put_port(port);
	return ret;
}

static void drm_dp_destroy_payload_at_remote_and_dfp(struct drm_dp_mst_topology_mgr *mgr,
						     struct drm_dp_mst_topology_state *mst_state,
						     struct drm_dp_mst_atomic_payload *payload)
{
	drm_dbg_kms(mgr->dev, "\n");

	/* it's okay for these to fail */
	if (payload->payload_allocation_status == DRM_DP_MST_PAYLOAD_ALLOCATION_REMOTE) {
		drm_dp_payload_send_msg(mgr, payload->port, payload->vcpi, 0);
		payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_DFP;
	}

	if (payload->payload_allocation_status == DRM_DP_MST_PAYLOAD_ALLOCATION_DFP)
		drm_dp_dpcd_write_payload(mgr, payload->vcpi, payload->vc_start_slot, 0);
}

/**
 * drm_dp_add_payload_part1() - Execute payload update part 1
 * @mgr: Manager to use.
 * @mst_state: The MST atomic state
 * @payload: The payload to write
 *
 * Determines the starting time slot for the given payload, and programs the VCPI for this payload
 * into the DPCD of DPRX. After calling this, the driver should generate ACT and payload packets.
 *
 * Returns: 0 on success, error code on failure.
 */
int drm_dp_add_payload_part1(struct drm_dp_mst_topology_mgr *mgr,
			     struct drm_dp_mst_topology_state *mst_state,
			     struct drm_dp_mst_atomic_payload *payload)
{
	struct drm_dp_mst_port *port;
	int ret;

	/* Update mst mgr info */
	if (mgr->payload_count == 0)
		mgr->next_start_slot = mst_state->start_slot;

	payload->vc_start_slot = mgr->next_start_slot;

	mgr->payload_count++;
	mgr->next_start_slot += payload->time_slots;

	payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_LOCAL;

	/* Allocate payload to immediate downstream facing port */
	port = drm_dp_mst_topology_get_port_validated(mgr, payload->port);
	if (!port) {
		drm_dbg_kms(mgr->dev,
			    "VCPI %d for port %p not in topology, not creating a payload to remote\n",
			    payload->vcpi, payload->port);
		return -EIO;
	}

	ret = drm_dp_create_payload_at_dfp(mgr, payload);
	if (ret < 0) {
		drm_dbg_kms(mgr->dev, "Failed to create MST payload for port %p: %d\n",
			    payload->port, ret);
		goto put_port;
	}

	payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_DFP;

put_port:
	drm_dp_mst_topology_put_port(port);

	return ret;
}
EXPORT_SYMBOL(drm_dp_add_payload_part1);

/**
 * drm_dp_remove_payload_part1() - Remove an MST payload along the virtual channel
 * @mgr: Manager to use.
 * @mst_state: The MST atomic state
 * @payload: The payload to remove
 *
 * Removes a payload along the virtual channel if it was successfully allocated.
 * After calling this, the driver should set HW to generate ACT and then switch to new
 * payload allocation state.
 */
void drm_dp_remove_payload_part1(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_topology_state *mst_state,
				 struct drm_dp_mst_atomic_payload *payload)
{
	/* Remove remote payload allocation */
	bool send_remove = false;

	mutex_lock(&mgr->lock);
	send_remove = drm_dp_mst_port_downstream_of_branch(payload->port, mgr->mst_primary);
	mutex_unlock(&mgr->lock);

	if (send_remove)
		drm_dp_destroy_payload_at_remote_and_dfp(mgr, mst_state, payload);
	else
		drm_dbg_kms(mgr->dev, "Payload for VCPI %d not in topology, not sending remove\n",
			    payload->vcpi);

	payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_LOCAL;
}
EXPORT_SYMBOL(drm_dp_remove_payload_part1);

/**
 * drm_dp_remove_payload_part2() - Remove an MST payload locally
 * @mgr: Manager to use.
 * @mst_state: The MST atomic state
 * @old_payload: The payload with its old state
 * @new_payload: The payload with its latest state
 *
 * Updates the starting time slots of all other payloads which would have been shifted towards
 * the start of the payload ID table as a result of removing a payload. Driver should call this
 * function whenever it removes a payload in its HW. It's independent to the result of payload
 * allocation/deallocation at branch devices along the virtual channel.
 */
void drm_dp_remove_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_topology_state *mst_state,
				 const struct drm_dp_mst_atomic_payload *old_payload,
				 struct drm_dp_mst_atomic_payload *new_payload)
{
	struct drm_dp_mst_atomic_payload *pos;

	/* Remove local payload allocation */
	list_for_each_entry(pos, &mst_state->payloads, next) {
		if (pos != new_payload && pos->vc_start_slot > new_payload->vc_start_slot)
			pos->vc_start_slot -= old_payload->time_slots;
	}
	new_payload->vc_start_slot = -1;

	mgr->payload_count--;
	mgr->next_start_slot -= old_payload->time_slots;

	if (new_payload->delete)
		drm_dp_mst_put_port_malloc(new_payload->port);

	new_payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_NONE;
}
EXPORT_SYMBOL(drm_dp_remove_payload_part2);
/**
 * drm_dp_add_payload_part2() - Execute payload update part 2
 * @mgr: Manager to use.
 * @state: The global atomic state
 * @payload: The payload to update
 *
 * If @payload was successfully assigned a starting time slot by drm_dp_add_payload_part1(), this
 * function will send the sideband messages to finish allocating this payload.
 *
 * Returns: 0 on success, negative error code on failure.
 */
int drm_dp_add_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
			     struct drm_atomic_state *state,
			     struct drm_dp_mst_atomic_payload *payload)
{
	int ret = 0;

	/* Skip failed payloads */
	if (payload->payload_allocation_status != DRM_DP_MST_PAYLOAD_ALLOCATION_DFP) {
		drm_dbg_kms(state->dev, "Part 1 of payload creation for %s failed, skipping part 2\n",
			    payload->port->connector->name);
		return -EIO;
	}

	/* Allocate payload to remote end */
	ret = drm_dp_create_payload_to_remote(mgr, payload);
	if (ret < 0)
		drm_err(mgr->dev, "Step 2 of creating MST payload for %p failed: %d\n",
			payload->port, ret);
	else
		payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_REMOTE;

	return ret;
}
EXPORT_SYMBOL(drm_dp_add_payload_part2);

static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_port *port,
				 int offset, int size, u8 *bytes)
{
	int ret = 0;
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_mst_branch *mstb;

	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
	if (!mstb)
		return -EINVAL;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		ret = -ENOMEM;
		goto fail_put;
	}

	build_dpcd_read(txmsg, port->port_num, offset, size);
	txmsg->dst = port->parent;

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret < 0)
		goto fail_free;

	if (txmsg->reply.reply_type == 1) {
		drm_dbg_kms(mgr->dev, "mstb %p port %d: DPCD read on addr 0x%x for %d bytes NAKed\n",
			    mstb, port->port_num, offset, size);
		ret = -EIO;
		goto fail_free;
	}

	if (txmsg->reply.u.remote_dpcd_read_ack.num_bytes != size) {
		ret = -EPROTO;
		goto fail_free;
	}

	ret = min_t(size_t, txmsg->reply.u.remote_dpcd_read_ack.num_bytes,
		    size);
	memcpy(bytes, txmsg->reply.u.remote_dpcd_read_ack.bytes, ret);

fail_free:
	kfree(txmsg);
fail_put:
	drm_dp_mst_topology_put_mstb(mstb);

	return ret;
}

static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
				  struct drm_dp_mst_port *port,
				  int offset, int size, u8 *bytes)
{
	int ret;
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_mst_branch *mstb;

	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
	if (!mstb)
		return -EINVAL;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		ret = -ENOMEM;
		goto fail_put;
	}

	build_dpcd_write(txmsg, port->port_num, offset, size, bytes);
	txmsg->dst = mstb;

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret > 0) {
		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
			ret = -EIO;
		else
			ret = size;
	}

	kfree(txmsg);
fail_put:
	drm_dp_mst_topology_put_mstb(mstb);
	return ret;
}

static int drm_dp_encode_up_ack_reply(struct drm_dp_sideband_msg_tx *msg, u8 req_type)
{
	struct drm_dp_sideband_msg_reply_body reply;

	reply.reply_type = DP_SIDEBAND_REPLY_ACK;
	reply.req_type = req_type;
	drm_dp_encode_sideband_reply(&reply, msg);
	return 0;
}

static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
				    struct drm_dp_mst_branch *mstb,
				    int req_type, bool broadcast)
{
	struct drm_dp_sideband_msg_tx *txmsg;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg)
		return -ENOMEM;

	txmsg->dst = mstb;
	drm_dp_encode_up_ack_reply(txmsg, req_type);

	mutex_lock(&mgr->qlock);
	/* construct a chunk from the first msg in the tx_msg queue */
	process_single_tx_qlock(mgr, txmsg, true);
	mutex_unlock(&mgr->qlock);

	kfree(txmsg);
	return 0;
}

/**
 * drm_dp_get_vc_payload_bw - get the VC payload BW for an MST link
 * @mgr: The &drm_dp_mst_topology_mgr to use
 * @link_rate: link rate in 10kbits/s units
 * @link_lane_count: lane count
 *
 * Calculate the total bandwidth of a MultiStream Transport link. The returned
 * value is in units of PBNs/(timeslots/1 MTP). This value can be used to
 * convert the number of PBNs required for a given stream to the number of
 * timeslots this stream requires in each MTP.
 *
 * Returns the BW / timeslot value in 20.12 fixed point format.
 */
fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
				    int link_rate, int link_lane_count)
{
	int ch_coding_efficiency =
		drm_dp_bw_channel_coding_efficiency(drm_dp_is_uhbr_rate(link_rate));
	fixed20_12 ret;

	if (link_rate == 0 || link_lane_count == 0)
		drm_dbg_kms(mgr->dev, "invalid link rate/lane count: (%d / %d)\n",
			    link_rate, link_lane_count);

	/* See DP v2.0 2.6.4.2, 2.7.6.3 VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
	ret.full = DIV_ROUND_DOWN_ULL(mul_u32_u32(link_rate * link_lane_count,
						  ch_coding_efficiency),
				      (1000000ULL * 8 * 5400) >> 12);

	return ret;
}
EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);

/**
 * drm_dp_read_mst_cap() - check whether or not a sink supports MST
 * @aux: The DP AUX channel to use
 * @dpcd: A cached copy of the DPCD capabilities for this sink
 *
 * Returns: %True if the sink supports MST, %false otherwise
 */
bool drm_dp_read_mst_cap(struct drm_dp_aux *aux,
			 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
{
	u8 mstm_cap;

	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_12)
		return false;

	if (drm_dp_dpcd_readb(aux, DP_MSTM_CAP, &mstm_cap) != 1)
		return false;

	return mstm_cap & DP_MST_CAP;
}
EXPORT_SYMBOL(drm_dp_read_mst_cap);

/**
 * drm_dp_mst_topology_mgr_set_mst() - Set the MST state for a topology manager
 * @mgr: manager to set state for
 * @mst_state: true to enable MST on this connector - false to disable.
 *
 * This is called by the driver when it detects an MST capable device plugged
 * into a DP MST capable port, or when a DP MST capable device is unplugged.
 */
int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state)
{
	int ret = 0;
	struct drm_dp_mst_branch *mstb = NULL;

	mutex_lock(&mgr->lock);
	if (mst_state == mgr->mst_state)
		goto out_unlock;

	mgr->mst_state = mst_state;
	/* set the device into MST mode */
	if (mst_state) {
		WARN_ON(mgr->mst_primary);

		/* get dpcd info */
		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
		if (ret < 0) {
			drm_dbg_kms(mgr->dev, "%s: failed to read DPCD, ret %d\n",
				    mgr->aux->name, ret);
			goto out_unlock;
		}

		/* add initial branch device at LCT 1 */
		mstb = drm_dp_add_mst_branch_device(1, NULL);
		if (mstb == NULL) {
			ret = -ENOMEM;
			goto out_unlock;
		}
		mstb->mgr = mgr;

		/* give this the main reference */
		mgr->mst_primary = mstb;
		drm_dp_mst_topology_get_mstb(mgr->mst_primary);

		ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
					 DP_MST_EN |
					 DP_UP_REQ_EN |
					 DP_UPSTREAM_IS_SRC);
		if (ret < 0)
			goto out_unlock;

		/* Write reset payload */
		drm_dp_dpcd_write_payload(mgr, 0, 0, 0x3f);

		queue_work(system_long_wq, &mgr->work);

		ret = 0;
	} else {
		/* disable MST on the device */
		mstb = mgr->mst_primary;
		mgr->mst_primary = NULL;
		/* this can fail if the device is gone */
		drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
		ret = 0;
		mgr->payload_id_table_cleared = false;

		memset(&mgr->down_rep_recv, 0, sizeof(mgr->down_rep_recv));
		memset(&mgr->up_req_recv, 0, sizeof(mgr->up_req_recv));
	}

out_unlock:
	mutex_unlock(&mgr->lock);
	if (mstb)
		drm_dp_mst_topology_put_mstb(mstb);
	return ret;

}
EXPORT_SYMBOL(drm_dp_mst_topology_mgr_set_mst);

static void
drm_dp_mst_topology_mgr_invalidate_mstb(struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_port *port;

	/* The link address will need to be re-sent on resume */
	mstb->link_address_sent = false;

	list_for_each_entry(port, &mstb->ports, next)
		if (port->mstb)
			drm_dp_mst_topology_mgr_invalidate_mstb(port->mstb);
}

/**
 * drm_dp_mst_topology_mgr_suspend() - suspend the MST manager
 * @mgr: manager to suspend
 *
 * This function tells the MST device that we can't handle UP messages
 * anymore. This should stop it from sending any since we are suspended.
 */
void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr)
{
	mutex_lock(&mgr->lock);
	drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
			   DP_MST_EN | DP_UPSTREAM_IS_SRC);
	mutex_unlock(&mgr->lock);
	flush_work(&mgr->up_req_work);
	flush_work(&mgr->work);
	flush_work(&mgr->delayed_destroy_work);

	mutex_lock(&mgr->lock);
	if (mgr->mst_state && mgr->mst_primary)
		drm_dp_mst_topology_mgr_invalidate_mstb(mgr->mst_primary);
	mutex_unlock(&mgr->lock);
}
EXPORT_SYMBOL(drm_dp_mst_topology_mgr_suspend);

/**
 * drm_dp_mst_topology_mgr_resume() - resume the MST manager
 * @mgr: manager to resume
 * @sync: whether or not to perform topology reprobing synchronously
 *
 * This will fetch DPCD and see if the device is still there,
 * if it is, it will rewrite the MSTM control bits, and return.
 *
 * If the device fails this returns -1, and the driver should do
 * a full MST reprobe, in case we were undocked.
 *
 * During system resume (where it is assumed that the driver will be calling
 * drm_atomic_helper_resume()) this function should be called beforehand with
 * @sync set to true. In contexts like runtime resume where the driver is not
 * expected to be calling drm_atomic_helper_resume(), this function should be
 * called with @sync set to false in order to avoid deadlocking.
 *
 * Returns: -1 if the MST topology was removed while we were suspended, 0
 * otherwise.
 */
int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr,
				   bool sync)
{
	int ret;
	u8 guid[16];

	mutex_lock(&mgr->lock);
	if (!mgr->mst_primary)
		goto out_fail;

	if (drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd) < 0) {
		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
		goto out_fail;
	}

	ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
				 DP_MST_EN |
				 DP_UP_REQ_EN |
				 DP_UPSTREAM_IS_SRC);
	if (ret < 0) {
		drm_dbg_kms(mgr->dev, "mst write failed - undocked during suspend?\n");
		goto out_fail;
	}

	/* Some hubs forget their guids after they resume */
	ret = drm_dp_dpcd_read(mgr->aux, DP_GUID, guid, 16);
	if (ret != 16) {
		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
		goto out_fail;
	}

	ret = drm_dp_check_mstb_guid(mgr->mst_primary, guid);
	if (ret) {
		drm_dbg_kms(mgr->dev, "check mstb failed - undocked during suspend?\n");
		goto out_fail;
	}

	/*
	 * For the final step of resuming the topology, we need to bring the
	 * state of our in-memory topology back into sync with reality. So,
	 * restart the probing process as if we're probing a new hub
	 */
	queue_work(system_long_wq, &mgr->work);
	mutex_unlock(&mgr->lock);

	if (sync) {
		drm_dbg_kms(mgr->dev,
			    "Waiting for link probe work to finish re-syncing topology...\n");
		flush_work(&mgr->work);
	}

	return 0;

out_fail:
	mutex_unlock(&mgr->lock);
	return -1;
}
EXPORT_SYMBOL(drm_dp_mst_topology_mgr_resume);

static bool
drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up,
		      struct drm_dp_mst_branch **mstb)
{
	int len;
	u8 replyblock[32];
	int replylen, curreply;
	int ret;
	u8 hdrlen;
	struct drm_dp_sideband_msg_hdr hdr;
	struct drm_dp_sideband_msg_rx *msg =
		up ? &mgr->up_req_recv : &mgr->down_rep_recv;
	int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE :
			   DP_SIDEBAND_MSG_DOWN_REP_BASE;

	if (!up)
		*mstb = NULL;

	len = min(mgr->max_dpcd_transaction_bytes, 16);
	ret = drm_dp_dpcd_read(mgr->aux, basereg, replyblock, len);
	if (ret != len) {
		drm_dbg_kms(mgr->dev, "failed to read DPCD down rep %d %d\n", len, ret);
		return false;
	}

	ret = drm_dp_decode_sideband_msg_hdr(mgr, &hdr, replyblock, len, &hdrlen);
	if (ret == false) {
		print_hex_dump(KERN_DEBUG, "failed hdr", DUMP_PREFIX_NONE, 16,
			       1, replyblock, len, false);
		drm_dbg_kms(mgr->dev, "ERROR: failed header\n");
		return false;
	}

	if (!up) {
		/* Caller is responsible for giving back this reference */
		*mstb = drm_dp_get_mst_branch_device(mgr, hdr.lct, hdr.rad);
		if (!*mstb) {
			drm_dbg_kms(mgr->dev, "Got MST reply from unknown device %d\n", hdr.lct);
			return false;
		}
	}

	if (!drm_dp_sideband_msg_set_header(msg, &hdr, hdrlen)) {
		drm_dbg_kms(mgr->dev, "sideband msg set header failed %d\n", replyblock[0]);
		return false;
	}

	replylen = min(msg->curchunk_len, (u8)(len - hdrlen));
	ret = drm_dp_sideband_append_payload(msg, replyblock + hdrlen, replylen);
	if (!ret) {
		drm_dbg_kms(mgr->dev, "sideband msg build failed %d\n", replyblock[0]);
		return false;
	}

	replylen = msg->curchunk_len + msg->curchunk_hdrlen - len;
	curreply = len;
	while (replylen > 0) {
		len = min3(replylen, mgr->max_dpcd_transaction_bytes, 16);
		ret = drm_dp_dpcd_read(mgr->aux, basereg + curreply,
				    replyblock, len);
		if (ret != len) {
			drm_dbg_kms(mgr->dev, "failed to read a chunk (len %d, ret %d)\n",
				    len, ret);
			return false;
		}

		ret = drm_dp_sideband_append_payload(msg, replyblock, len);
		if (!ret) {
			drm_dbg_kms(mgr->dev, "failed to build sideband msg\n");
			return false;
		}

		curreply += len;
		replylen -= len;
	}
	return true;
}

static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_mst_branch *mstb = NULL;
	struct drm_dp_sideband_msg_rx *msg = &mgr->down_rep_recv;

	if (!drm_dp_get_one_sb_msg(mgr, false, &mstb))
		goto out_clear_reply;

	/* Multi-packet message transmission, don't clear the reply */
	if (!msg->have_eomt)
		goto out;

	/* find the message */
	mutex_lock(&mgr->qlock);
	txmsg = list_first_entry_or_null(&mgr->tx_msg_downq,
					 struct drm_dp_sideband_msg_tx, next);
	mutex_unlock(&mgr->qlock);

	/* Were we actually expecting a response, and from this mstb? */
	if (!txmsg || txmsg->dst != mstb) {
		struct drm_dp_sideband_msg_hdr *hdr;

		hdr = &msg->initial_hdr;
		drm_dbg_kms(mgr->dev, "Got MST reply with no msg %p %d %d %02x %02x\n",
			    mstb, hdr->seqno, hdr->lct, hdr->rad[0], msg->msg[0]);
		goto out_clear_reply;
	}

	drm_dp_sideband_parse_reply(mgr, msg, &txmsg->reply);

	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
		drm_dbg_kms(mgr->dev,
			    "Got NAK reply: req 0x%02x (%s), reason 0x%02x (%s), nak data 0x%02x\n",
			    txmsg->reply.req_type,
			    drm_dp_mst_req_type_str(txmsg->reply.req_type),
			    txmsg->reply.u.nak.reason,
			    drm_dp_mst_nak_reason_str(txmsg->reply.u.nak.reason),
			    txmsg->reply.u.nak.nak_data);
	}

	memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
	drm_dp_mst_topology_put_mstb(mstb);

	mutex_lock(&mgr->qlock);
	txmsg->state = DRM_DP_SIDEBAND_TX_RX;
	list_del(&txmsg->next);
	mutex_unlock(&mgr->qlock);

	wake_up_all(&mgr->tx_waitq);

	return 0;

out_clear_reply:
	memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
out:
	if (mstb)
		drm_dp_mst_topology_put_mstb(mstb);

	return 0;
}

static inline bool
drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
			  struct drm_dp_pending_up_req *up_req)
{
	struct drm_dp_mst_branch *mstb = NULL;
	struct drm_dp_sideband_msg_req_body *msg = &up_req->msg;
	struct drm_dp_sideband_msg_hdr *hdr = &up_req->hdr;
	bool hotplug = false, dowork = false;

	if (hdr->broadcast) {
		const u8 *guid = NULL;

		if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY)
			guid = msg->u.conn_stat.guid;
		else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
			guid = msg->u.resource_stat.guid;

		if (guid)
			mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
	} else {
		mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
	}

	if (!mstb) {
		drm_dbg_kms(mgr->dev, "Got MST reply from unknown device %d\n", hdr->lct);
		return false;
	}

	/* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */
	if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
		dowork = drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat);
		hotplug = true;
	}

	drm_dp_mst_topology_put_mstb(mstb);

	if (dowork)
		queue_work(system_long_wq, &mgr->work);
	return hotplug;
}

static void drm_dp_mst_up_req_work(struct work_struct *work)
{
	struct drm_dp_mst_topology_mgr *mgr =
		container_of(work, struct drm_dp_mst_topology_mgr,
			     up_req_work);
	struct drm_dp_pending_up_req *up_req;
	bool send_hotplug = false;

	mutex_lock(&mgr->probe_lock);
	while (true) {
		mutex_lock(&mgr->up_req_lock);
		up_req = list_first_entry_or_null(&mgr->up_req_list,
						  struct drm_dp_pending_up_req,
						  next);
		if (up_req)
			list_del(&up_req->next);
		mutex_unlock(&mgr->up_req_lock);

		if (!up_req)
			break;

		send_hotplug |= drm_dp_mst_process_up_req(mgr, up_req);
		kfree(up_req);
	}
	mutex_unlock(&mgr->probe_lock);

	if (send_hotplug)
		drm_kms_helper_hotplug_event(mgr->dev);
}

static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_pending_up_req *up_req;

	if (!drm_dp_get_one_sb_msg(mgr, true, NULL))
		goto out;

	if (!mgr->up_req_recv.have_eomt)
		return 0;

	up_req = kzalloc(sizeof(*up_req), GFP_KERNEL);
	if (!up_req)
		return -ENOMEM;

	INIT_LIST_HEAD(&up_req->next);

	drm_dp_sideband_parse_req(mgr, &mgr->up_req_recv, &up_req->msg);

	if (up_req->msg.req_type != DP_CONNECTION_STATUS_NOTIFY &&
	    up_req->msg.req_type != DP_RESOURCE_STATUS_NOTIFY) {
		drm_dbg_kms(mgr->dev, "Received unknown up req type, ignoring: %x\n",
			    up_req->msg.req_type);
		kfree(up_req);
		goto out;
	}

	drm_dp_send_up_ack_reply(mgr, mgr->mst_primary, up_req->msg.req_type,
				 false);

	if (up_req->msg.req_type == DP_CONNECTION_STATUS_NOTIFY) {
		const struct drm_dp_connection_status_notify *conn_stat =
			&up_req->msg.u.conn_stat;

		drm_dbg_kms(mgr->dev, "Got CSN: pn: %d ldps:%d ddps: %d mcs: %d ip: %d pdt: %d\n",
			    conn_stat->port_number,
			    conn_stat->legacy_device_plug_status,
			    conn_stat->displayport_device_plug_status,
			    conn_stat->message_capability_status,
			    conn_stat->input_port,
			    conn_stat->peer_device_type);
	} else if (up_req->msg.req_type == DP_RESOURCE_STATUS_NOTIFY) {
		const struct drm_dp_resource_status_notify *res_stat =
			&up_req->msg.u.resource_stat;

		drm_dbg_kms(mgr->dev, "Got RSN: pn: %d avail_pbn %d\n",
			    res_stat->port_number,
			    res_stat->available_pbn);
	}

	up_req->hdr = mgr->up_req_recv.initial_hdr;
	mutex_lock(&mgr->up_req_lock);
	list_add_tail(&up_req->next, &mgr->up_req_list);
	mutex_unlock(&mgr->up_req_lock);
	queue_work(system_long_wq, &mgr->up_req_work);

out:
	memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
	return 0;
}

/**
 * drm_dp_mst_hpd_irq_handle_event() - MST hotplug IRQ handle MST event
 * @mgr: manager to notify irq for.
 * @esi: 4 bytes from SINK_COUNT_ESI
 * @ack: 4 bytes used to ack events starting from SINK_COUNT_ESI
 * @handled: whether the hpd interrupt was consumed or not
 *
 * This should be called from the driver when it detects a HPD IRQ,
 * along with the value of the DEVICE_SERVICE_IRQ_VECTOR_ESI0. The
 * topology manager will process the sideband messages received
 * as indicated in the DEVICE_SERVICE_IRQ_VECTOR_ESI0 and set the
 * corresponding flags that Driver has to ack the DP receiver later.
 *
 * Note that driver shall also call
 * drm_dp_mst_hpd_irq_send_new_request() if the 'handled' is set
 * after calling this function, to try to kick off a new request in
 * the queue if the previous message transaction is completed.
 *
 * See also:
 * drm_dp_mst_hpd_irq_send_new_request()
 */
int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr *mgr, const u8 *esi,
				    u8 *ack, bool *handled)
{
	int ret = 0;
	int sc;
	*handled = false;
	sc = DP_GET_SINK_COUNT(esi[0]);

	if (sc != mgr->sink_count) {
		mgr->sink_count = sc;
		*handled = true;
	}

	if (esi[1] & DP_DOWN_REP_MSG_RDY) {
		ret = drm_dp_mst_handle_down_rep(mgr);
		*handled = true;
		ack[1] |= DP_DOWN_REP_MSG_RDY;
	}

	if (esi[1] & DP_UP_REQ_MSG_RDY) {
		ret |= drm_dp_mst_handle_up_req(mgr);
		*handled = true;
		ack[1] |= DP_UP_REQ_MSG_RDY;
	}

	return ret;
}
EXPORT_SYMBOL(drm_dp_mst_hpd_irq_handle_event);

/**
 * drm_dp_mst_hpd_irq_send_new_request() - MST hotplug IRQ kick off new request
 * @mgr: manager to notify irq for.
 *
 * This should be called from the driver when mst irq event is handled
 * and acked. Note that new down request should only be sent when
 * previous message transaction is completed. Source is not supposed to generate
 * interleaved message transactions.
 */
void drm_dp_mst_hpd_irq_send_new_request(struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	bool kick = true;

	mutex_lock(&mgr->qlock);
	txmsg = list_first_entry_or_null(&mgr->tx_msg_downq,
					 struct drm_dp_sideband_msg_tx, next);
	/* If last transaction is not completed yet*/
	if (!txmsg ||
	    txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
	    txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
		kick = false;
	mutex_unlock(&mgr->qlock);

	if (kick)
		drm_dp_mst_kick_tx(mgr);
}
EXPORT_SYMBOL(drm_dp_mst_hpd_irq_send_new_request);
/**
 * drm_dp_mst_detect_port() - get connection status for an MST port
 * @connector: DRM connector for this port
 * @ctx: The acquisition context to use for grabbing locks
 * @mgr: manager for this port
 * @port: pointer to a port
 *
 * This returns the current connection state for a port.
 */
int
drm_dp_mst_detect_port(struct drm_connector *connector,
		       struct drm_modeset_acquire_ctx *ctx,
		       struct drm_dp_mst_topology_mgr *mgr,
		       struct drm_dp_mst_port *port)
{
	int ret;

	/* we need to search for the port in the mgr in case it's gone */
	port = drm_dp_mst_topology_get_port_validated(mgr, port);
	if (!port)
		return connector_status_disconnected;

	ret = drm_modeset_lock(&mgr->base.lock, ctx);
	if (ret)
		goto out;

	ret = connector_status_disconnected;

	if (!port->ddps)
		goto out;

	switch (port->pdt) {
	case DP_PEER_DEVICE_NONE:
		break;
	case DP_PEER_DEVICE_MST_BRANCHING:
		if (!port->mcs)
			ret = connector_status_connected;
		break;

	case DP_PEER_DEVICE_SST_SINK:
		ret = connector_status_connected;
		/* for logical ports - cache the EDID */
		if (port->port_num >= DP_MST_LOGICAL_PORT_0 && !port->cached_edid)
			port->cached_edid = drm_edid_read_ddc(connector, &port->aux.ddc);
		break;
	case DP_PEER_DEVICE_DP_LEGACY_CONV:
		if (port->ldps)
			ret = connector_status_connected;
		break;
	}
out:
	drm_dp_mst_topology_put_port(port);
	return ret;
}
EXPORT_SYMBOL(drm_dp_mst_detect_port);

/**
 * drm_dp_mst_edid_read() - get EDID for an MST port
 * @connector: toplevel connector to get EDID for
 * @mgr: manager for this port
 * @port: unverified pointer to a port.
 *
 * This returns an EDID for the port connected to a connector,
 * It validates the pointer still exists so the caller doesn't require a
 * reference.
 */
const struct drm_edid *drm_dp_mst_edid_read(struct drm_connector *connector,
					    struct drm_dp_mst_topology_mgr *mgr,
					    struct drm_dp_mst_port *port)
{
	const struct drm_edid *drm_edid;

	/* we need to search for the port in the mgr in case it's gone */
	port = drm_dp_mst_topology_get_port_validated(mgr, port);
	if (!port)
		return NULL;

	if (port->cached_edid)
		drm_edid = drm_edid_dup(port->cached_edid);
	else
		drm_edid = drm_edid_read_ddc(connector, &port->aux.ddc);

	drm_dp_mst_topology_put_port(port);

	return drm_edid;
}
EXPORT_SYMBOL(drm_dp_mst_edid_read);

/**
 * drm_dp_mst_get_edid() - get EDID for an MST port
 * @connector: toplevel connector to get EDID for
 * @mgr: manager for this port
 * @port: unverified pointer to a port.
 *
 * This function is deprecated; please use drm_dp_mst_edid_read() instead.
 *
 * This returns an EDID for the port connected to a connector,
 * It validates the pointer still exists so the caller doesn't require a
 * reference.
 */
struct edid *drm_dp_mst_get_edid(struct drm_connector *connector,
				 struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_port *port)
{
	const struct drm_edid *drm_edid;
	struct edid *edid;

	drm_edid = drm_dp_mst_edid_read(connector, mgr, port);

	edid = drm_edid_duplicate(drm_edid_raw(drm_edid));

	drm_edid_free(drm_edid);

	return edid;
}
EXPORT_SYMBOL(drm_dp_mst_get_edid);

/**
 * drm_dp_atomic_find_time_slots() - Find and add time slots to the state
 * @state: global atomic state
 * @mgr: MST topology manager for the port
 * @port: port to find time slots for
 * @pbn: bandwidth required for the mode in PBN
 *
 * Allocates time slots to @port, replacing any previous time slot allocations it may
 * have had. Any atomic drivers which support MST must call this function in
 * their &drm_encoder_helper_funcs.atomic_check() callback unconditionally to
 * change the current time slot allocation for the new state, and ensure the MST
 * atomic state is added whenever the state of payloads in the topology changes.
 *
 * Allocations set by this function are not checked against the bandwidth
 * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
 *
 * Additionally, it is OK to call this function multiple times on the same
 * @port as needed. It is not OK however, to call this function and
 * drm_dp_atomic_release_time_slots() in the same atomic check phase.
 *
 * See also:
 * drm_dp_atomic_release_time_slots()
 * drm_dp_mst_atomic_check()
 *
 * Returns:
 * Total slots in the atomic state assigned for this port, or a negative error
 * code if the port no longer exists
 */
int drm_dp_atomic_find_time_slots(struct drm_atomic_state *state,
				  struct drm_dp_mst_topology_mgr *mgr,
				  struct drm_dp_mst_port *port, int pbn)
{
	struct drm_dp_mst_topology_state *topology_state;
	struct drm_dp_mst_atomic_payload *payload = NULL;
	struct drm_connector_state *conn_state;
	int prev_slots = 0, prev_bw = 0, req_slots;

	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
	if (IS_ERR(topology_state))
		return PTR_ERR(topology_state);

	conn_state = drm_atomic_get_new_connector_state(state, port->connector);
	topology_state->pending_crtc_mask |= drm_crtc_mask(conn_state->crtc);

	/* Find the current allocation for this port, if any */
	payload = drm_atomic_get_mst_payload_state(topology_state, port);
	if (payload) {
		prev_slots = payload->time_slots;
		prev_bw = payload->pbn;

		/*
		 * This should never happen, unless the driver tries
		 * releasing and allocating the same timeslot allocation,
		 * which is an error
		 */
		if (drm_WARN_ON(mgr->dev, payload->delete)) {
			drm_err(mgr->dev,
				"cannot allocate and release time slots on [MST PORT:%p] in the same state\n",
				port);
			return -EINVAL;
		}
	}

	req_slots = DIV_ROUND_UP(dfixed_const(pbn), topology_state->pbn_div.full);

	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] TU %d -> %d\n",
		       port->connector->base.id, port->connector->name,
		       port, prev_slots, req_slots);
	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] PBN %d -> %d\n",
		       port->connector->base.id, port->connector->name,
		       port, prev_bw, pbn);

	/* Add the new allocation to the state, note the VCPI isn't assigned until the end */
	if (!payload) {
		payload = kzalloc(sizeof(*payload), GFP_KERNEL);
		if (!payload)
			return -ENOMEM;

		drm_dp_mst_get_port_malloc(port);
		payload->port = port;
		payload->vc_start_slot = -1;
		payload->payload_allocation_status = DRM_DP_MST_PAYLOAD_ALLOCATION_NONE;
		list_add(&payload->next, &topology_state->payloads);
	}
	payload->time_slots = req_slots;
	payload->pbn = pbn;

	return req_slots;
}
EXPORT_SYMBOL(drm_dp_atomic_find_time_slots);

/**
 * drm_dp_atomic_release_time_slots() - Release allocated time slots
 * @state: global atomic state
 * @mgr: MST topology manager for the port
 * @port: The port to release the time slots from
 *
 * Releases any time slots that have been allocated to a port in the atomic
 * state. Any atomic drivers which support MST must call this function
 * unconditionally in their &drm_connector_helper_funcs.atomic_check() callback.
 * This helper will check whether time slots would be released by the new state and
 * respond accordingly, along with ensuring the MST state is always added to the
 * atomic state whenever a new state would modify the state of payloads on the
 * topology.
 *
 * It is OK to call this even if @port has been removed from the system.
 * Additionally, it is OK to call this function multiple times on the same
 * @port as needed. It is not OK however, to call this function and
 * drm_dp_atomic_find_time_slots() on the same @port in a single atomic check
 * phase.
 *
 * See also:
 * drm_dp_atomic_find_time_slots()
 * drm_dp_mst_atomic_check()
 *
 * Returns:
 * 0 on success, negative error code otherwise
 */
int drm_dp_atomic_release_time_slots(struct drm_atomic_state *state,
				     struct drm_dp_mst_topology_mgr *mgr,
				     struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_topology_state *topology_state;
	struct drm_dp_mst_atomic_payload *payload;
	struct drm_connector_state *old_conn_state, *new_conn_state;
	bool update_payload = true;

	old_conn_state = drm_atomic_get_old_connector_state(state, port->connector);
	if (!old_conn_state->crtc)
		return 0;

	/* If the CRTC isn't disabled by this state, don't release it's payload */
	new_conn_state = drm_atomic_get_new_connector_state(state, port->connector);
	if (new_conn_state->crtc) {
		struct drm_crtc_state *crtc_state =
			drm_atomic_get_new_crtc_state(state, new_conn_state->crtc);

		/* No modeset means no payload changes, so it's safe to not pull in the MST state */
		if (!crtc_state || !drm_atomic_crtc_needs_modeset(crtc_state))
			return 0;

		if (!crtc_state->mode_changed && !crtc_state->connectors_changed)
			update_payload = false;
	}

	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
	if (IS_ERR(topology_state))
		return PTR_ERR(topology_state);

	topology_state->pending_crtc_mask |= drm_crtc_mask(old_conn_state->crtc);
	if (!update_payload)
		return 0;

	payload = drm_atomic_get_mst_payload_state(topology_state, port);
	if (WARN_ON(!payload)) {
		drm_err(mgr->dev, "No payload for [MST PORT:%p] found in mst state %p\n",
			port, &topology_state->base);
		return -EINVAL;
	}

	if (new_conn_state->crtc)
		return 0;

	drm_dbg_atomic(mgr->dev, "[MST PORT:%p] TU %d -> 0\n", port, payload->time_slots);
	if (!payload->delete) {
		payload->pbn = 0;
		payload->delete = true;
		topology_state->payload_mask &= ~BIT(payload->vcpi - 1);
	}

	return 0;
}
EXPORT_SYMBOL(drm_dp_atomic_release_time_slots);

/**
 * drm_dp_mst_atomic_setup_commit() - setup_commit hook for MST helpers
 * @state: global atomic state
 *
 * This function saves all of the &drm_crtc_commit structs in an atomic state that touch any CRTCs
 * currently assigned to an MST topology. Drivers must call this hook from their
 * &drm_mode_config_helper_funcs.atomic_commit_setup hook.
 *
 * Returns:
 * 0 if all CRTC commits were retrieved successfully, negative error code otherwise
 */
int drm_dp_mst_atomic_setup_commit(struct drm_atomic_state *state)
{
	struct drm_dp_mst_topology_mgr *mgr;
	struct drm_dp_mst_topology_state *mst_state;
	struct drm_crtc *crtc;
	struct drm_crtc_state *crtc_state;
	int i, j, commit_idx, num_commit_deps;

	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
		if (!mst_state->pending_crtc_mask)
			continue;

		num_commit_deps = hweight32(mst_state->pending_crtc_mask);
		mst_state->commit_deps = kmalloc_array(num_commit_deps,
						       sizeof(*mst_state->commit_deps), GFP_KERNEL);
		if (!mst_state->commit_deps)
			return -ENOMEM;
		mst_state->num_commit_deps = num_commit_deps;

		commit_idx = 0;
		for_each_new_crtc_in_state(state, crtc, crtc_state, j) {
			if (mst_state->pending_crtc_mask & drm_crtc_mask(crtc)) {
				mst_state->commit_deps[commit_idx++] =
					drm_crtc_commit_get(crtc_state->commit);
			}
		}
	}

	return 0;
}
EXPORT_SYMBOL(drm_dp_mst_atomic_setup_commit);

/**
 * drm_dp_mst_atomic_wait_for_dependencies() - Wait for all pending commits on MST topologies,
 * prepare new MST state for commit
 * @state: global atomic state
 *
 * Goes through any MST topologies in this atomic state, and waits for any pending commits which
 * touched CRTCs that were/are on an MST topology to be programmed to hardware and flipped to before
 * returning. This is to prevent multiple non-blocking commits affecting an MST topology from racing
 * with eachother by forcing them to be executed sequentially in situations where the only resources
 * the modeset objects in these commits share are an MST topology.
 *
 * This function also prepares the new MST state for commit by performing some state preparation
 * which can't be done until this point, such as reading back the final VC start slots (which are
 * determined at commit-time) from the previous state.
 *
 * All MST drivers must call this function after calling drm_atomic_helper_wait_for_dependencies(),
 * or whatever their equivalent of that is.
 */
void drm_dp_mst_atomic_wait_for_dependencies(struct drm_atomic_state *state)
{
	struct drm_dp_mst_topology_state *old_mst_state, *new_mst_state;
	struct drm_dp_mst_topology_mgr *mgr;
	struct drm_dp_mst_atomic_payload *old_payload, *new_payload;
	int i, j, ret;

	for_each_oldnew_mst_mgr_in_state(state, mgr, old_mst_state, new_mst_state, i) {
		for (j = 0; j < old_mst_state->num_commit_deps; j++) {
			ret = drm_crtc_commit_wait(old_mst_state->commit_deps[j]);
			if (ret < 0)
				drm_err(state->dev, "Failed to wait for %s: %d\n",
					old_mst_state->commit_deps[j]->crtc->name, ret);
		}

		/* Now that previous state is committed, it's safe to copy over the start slot
		 * and allocation status assignments
		 */
		list_for_each_entry(old_payload, &old_mst_state->payloads, next) {
			if (old_payload->delete)
				continue;

			new_payload = drm_atomic_get_mst_payload_state(new_mst_state,
								       old_payload->port);
			new_payload->vc_start_slot = old_payload->vc_start_slot;
			new_payload->payload_allocation_status =
							old_payload->payload_allocation_status;
		}
	}
}
EXPORT_SYMBOL(drm_dp_mst_atomic_wait_for_dependencies);

/**
 * drm_dp_mst_root_conn_atomic_check() - Serialize CRTC commits on MST-capable connectors operating
 * in SST mode
 * @new_conn_state: The new connector state of the &drm_connector
 * @mgr: The MST topology manager for the &drm_connector
 *
 * Since MST uses fake &drm_encoder structs, the generic atomic modesetting code isn't able to
 * serialize non-blocking commits happening on the real DP connector of an MST topology switching
 * into/away from MST mode - as the CRTC on the real DP connector and the CRTCs on the connector's
 * MST topology will never share the same &drm_encoder.
 *
 * This function takes care of this serialization issue, by checking a root MST connector's atomic
 * state to determine if it is about to have a modeset - and then pulling in the MST topology state
 * if so, along with adding any relevant CRTCs to &drm_dp_mst_topology_state.pending_crtc_mask.
 *
 * Drivers implementing MST must call this function from the
 * &drm_connector_helper_funcs.atomic_check hook of any physical DP &drm_connector capable of
 * driving MST sinks.
 *
 * Returns:
 * 0 on success, negative error code otherwise
 */
int drm_dp_mst_root_conn_atomic_check(struct drm_connector_state *new_conn_state,
				      struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_atomic_state *state = new_conn_state->state;
	struct drm_connector_state *old_conn_state =
		drm_atomic_get_old_connector_state(state, new_conn_state->connector);
	struct drm_crtc_state *crtc_state;
	struct drm_dp_mst_topology_state *mst_state = NULL;

	if (new_conn_state->crtc) {
		crtc_state = drm_atomic_get_new_crtc_state(state, new_conn_state->crtc);
		if (crtc_state && drm_atomic_crtc_needs_modeset(crtc_state)) {
			mst_state = drm_atomic_get_mst_topology_state(state, mgr);
			if (IS_ERR(mst_state))
				return PTR_ERR(mst_state);

			mst_state->pending_crtc_mask |= drm_crtc_mask(new_conn_state->crtc);
		}
	}

	if (old_conn_state->crtc) {
		crtc_state = drm_atomic_get_new_crtc_state(state, old_conn_state->crtc);
		if (crtc_state && drm_atomic_crtc_needs_modeset(crtc_state)) {
			if (!mst_state) {
				mst_state = drm_atomic_get_mst_topology_state(state, mgr);
				if (IS_ERR(mst_state))
					return PTR_ERR(mst_state);
			}

			mst_state->pending_crtc_mask |= drm_crtc_mask(old_conn_state->crtc);
		}
	}

	return 0;
}
EXPORT_SYMBOL(drm_dp_mst_root_conn_atomic_check);

/**
 * drm_dp_mst_update_slots() - updates the slot info depending on the DP ecoding format
 * @mst_state: mst_state to update
 * @link_encoding_cap: the ecoding format on the link
 */
void drm_dp_mst_update_slots(struct drm_dp_mst_topology_state *mst_state, uint8_t link_encoding_cap)
{
	if (link_encoding_cap == DP_CAP_ANSI_128B132B) {
		mst_state->total_avail_slots = 64;
		mst_state->start_slot = 0;
	} else {
		mst_state->total_avail_slots = 63;
		mst_state->start_slot = 1;
	}

	DRM_DEBUG_KMS("%s encoding format on mst_state 0x%p\n",
		      (link_encoding_cap == DP_CAP_ANSI_128B132B) ? "128b/132b":"8b/10b",
		      mst_state);
}
EXPORT_SYMBOL(drm_dp_mst_update_slots);

static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
				     int id, u8 start_slot, u8 num_slots)
{
	u8 payload_alloc[3], status;
	int ret;
	int retries = 0;

	drm_dp_dpcd_writeb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS,
			   DP_PAYLOAD_TABLE_UPDATED);

	payload_alloc[0] = id;
	payload_alloc[1] = start_slot;
	payload_alloc[2] = num_slots;

	ret = drm_dp_dpcd_write(mgr->aux, DP_PAYLOAD_ALLOCATE_SET, payload_alloc, 3);
	if (ret != 3) {
		drm_dbg_kms(mgr->dev, "failed to write payload allocation %d\n", ret);
		goto fail;
	}

retry:
	ret = drm_dp_dpcd_readb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status);
	if (ret < 0) {
		drm_dbg_kms(mgr->dev, "failed to read payload table status %d\n", ret);
		goto fail;
	}

	if (!(status & DP_PAYLOAD_TABLE_UPDATED)) {
		retries++;
		if (retries < 20) {
			usleep_range(10000, 20000);
			goto retry;
		}
		drm_dbg_kms(mgr->dev, "status not set after read payload table status %d\n",
			    status);
		ret = -EINVAL;
		goto fail;
	}
	ret = 0;
fail:
	return ret;
}

static int do_get_act_status(struct drm_dp_aux *aux)
{
	int ret;
	u8 status;

	ret = drm_dp_dpcd_readb(aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status);
	if (ret < 0)
		return ret;

	return status;
}

/**
 * drm_dp_check_act_status() - Polls for ACT handled status.
 * @mgr: manager to use
 *
 * Tries waiting for the MST hub to finish updating it's payload table by
 * polling for the ACT handled bit for up to 3 seconds (yes-some hubs really
 * take that long).
 *
 * Returns:
 * 0 if the ACT was handled in time, negative error code on failure.
 */
int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
{
	/*
	 * There doesn't seem to be any recommended retry count or timeout in
	 * the MST specification. Since some hubs have been observed to take
	 * over 1 second to update their payload allocations under certain
	 * conditions, we use a rather large timeout value.
	 */
	const int timeout_ms = 3000;
	int ret, status;

	ret = readx_poll_timeout(do_get_act_status, mgr->aux, status,
				 status & DP_PAYLOAD_ACT_HANDLED || status < 0,
				 200, timeout_ms * USEC_PER_MSEC);
	if (ret < 0 && status >= 0) {
		drm_err(mgr->dev, "Failed to get ACT after %dms, last status: %02x\n",
			timeout_ms, status);
		return -EINVAL;
	} else if (status < 0) {
		/*
		 * Failure here isn't unexpected - the hub may have
		 * just been unplugged
		 */
		drm_dbg_kms(mgr->dev, "Failed to read payload table status: %d\n", status);
		return status;
	}

	return 0;
}
EXPORT_SYMBOL(drm_dp_check_act_status);

/**
 * drm_dp_calc_pbn_mode() - Calculate the PBN for a mode.
 * @clock: dot clock
 * @bpp: bpp as .4 binary fixed point
 *
 * This uses the formula in the spec to calculate the PBN value for a mode.
 */
int drm_dp_calc_pbn_mode(int clock, int bpp)
{
	/*
	 * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
	 * common multiplier to render an integer PBN for all link rate/lane
	 * counts combinations
	 * calculate
	 * peak_kbps = clock * bpp / 16
	 * peak_kbps *= SSC overhead / 1000000
	 * peak_kbps /= 8    convert to Kbytes
	 * peak_kBps *= (64/54) / 1000    convert to PBN
	 */
	/*
	 * TODO: Use the actual link and mode parameters to calculate
	 * the overhead. For now it's assumed that these are
	 * 4 link lanes, 4096 hactive pixels, which don't add any
	 * significant data padding overhead and that there is no DSC
	 * or FEC overhead.
	 */
	int overhead = drm_dp_bw_overhead(4, 4096, 0, bpp,
					  DRM_DP_BW_OVERHEAD_MST |
					  DRM_DP_BW_OVERHEAD_SSC_REF_CLK);

	return DIV64_U64_ROUND_UP(mul_u32_u32(clock * bpp, 64 * overhead >> 4),
				  1000000ULL * 8 * 54 * 1000);
}
EXPORT_SYMBOL(drm_dp_calc_pbn_mode);

/* we want to kick the TX after we've ack the up/down IRQs. */
static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr)
{
	queue_work(system_long_wq, &mgr->tx_work);
}

/*
 * Helper function for parsing DP device types into convenient strings
 * for use with dp_mst_topology
 */
static const char *pdt_to_string(u8 pdt)
{
	switch (pdt) {
	case DP_PEER_DEVICE_NONE:
		return "NONE";
	case DP_PEER_DEVICE_SOURCE_OR_SST:
		return "SOURCE OR SST";
	case DP_PEER_DEVICE_MST_BRANCHING:
		return "MST BRANCHING";
	case DP_PEER_DEVICE_SST_SINK:
		return "SST SINK";
	case DP_PEER_DEVICE_DP_LEGACY_CONV:
		return "DP LEGACY CONV";
	default:
		return "ERR";
	}
}

static void drm_dp_mst_dump_mstb(struct seq_file *m,
				 struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_port *port;
	int tabs = mstb->lct;
	char prefix[10];
	int i;

	for (i = 0; i < tabs; i++)
		prefix[i] = '\t';
	prefix[i] = '\0';

	seq_printf(m, "%smstb - [%p]: num_ports: %d\n", prefix, mstb, mstb->num_ports);
	list_for_each_entry(port, &mstb->ports, next) {
		seq_printf(m, "%sport %d - [%p] (%s - %s): ddps: %d, ldps: %d, sdp: %d/%d, fec: %s, conn: %p\n",
			   prefix,
			   port->port_num,
			   port,
			   port->input ? "input" : "output",
			   pdt_to_string(port->pdt),
			   port->ddps,
			   port->ldps,
			   port->num_sdp_streams,
			   port->num_sdp_stream_sinks,
			   port->fec_capable ? "true" : "false",
			   port->connector);
		if (port->mstb)
			drm_dp_mst_dump_mstb(m, port->mstb);
	}
}

#define DP_PAYLOAD_TABLE_SIZE		64

static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
				  char *buf)
{
	int i;

	for (i = 0; i < DP_PAYLOAD_TABLE_SIZE; i += 16) {
		if (drm_dp_dpcd_read(mgr->aux,
				     DP_PAYLOAD_TABLE_UPDATE_STATUS + i,
				     &buf[i], 16) != 16)
			return false;
	}
	return true;
}

static void fetch_monitor_name(struct drm_dp_mst_topology_mgr *mgr,
			       struct drm_dp_mst_port *port, char *name,
			       int namelen)
{
	struct edid *mst_edid;

	mst_edid = drm_dp_mst_get_edid(port->connector, mgr, port);
	drm_edid_get_monitor_name(mst_edid, name, namelen);
	kfree(mst_edid);
}

/**
 * drm_dp_mst_dump_topology(): dump topology to seq file.
 * @m: seq_file to dump output to
 * @mgr: manager to dump current topology for.
 *
 * helper to dump MST topology to a seq file for debugfs.
 */
void drm_dp_mst_dump_topology(struct seq_file *m,
			      struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_mst_topology_state *state;
	struct drm_dp_mst_atomic_payload *payload;
	int i, ret;

	static const char *const status[] = {
		"None",
		"Local",
		"DFP",
		"Remote",
	};

	mutex_lock(&mgr->lock);
	if (mgr->mst_primary)
		drm_dp_mst_dump_mstb(m, mgr->mst_primary);

	/* dump VCPIs */
	mutex_unlock(&mgr->lock);

	ret = drm_modeset_lock_single_interruptible(&mgr->base.lock);
	if (ret < 0)
		return;

	state = to_drm_dp_mst_topology_state(mgr->base.state);
	seq_printf(m, "\n*** Atomic state info ***\n");
	seq_printf(m, "payload_mask: %x, max_payloads: %d, start_slot: %u, pbn_div: %d\n",
		   state->payload_mask, mgr->max_payloads, state->start_slot,
		   dfixed_trunc(state->pbn_div));

	seq_printf(m, "\n| idx | port | vcpi | slots | pbn | dsc | status |     sink name     |\n");
	for (i = 0; i < mgr->max_payloads; i++) {
		list_for_each_entry(payload, &state->payloads, next) {
			char name[14];

			if (payload->vcpi != i || payload->delete)
				continue;

			fetch_monitor_name(mgr, payload->port, name, sizeof(name));
			seq_printf(m, " %5d %6d %6d %02d - %02d %5d %5s %8s %19s\n",
				   i,
				   payload->port->port_num,
				   payload->vcpi,
				   payload->vc_start_slot,
				   payload->vc_start_slot + payload->time_slots - 1,
				   payload->pbn,
				   payload->dsc_enabled ? "Y" : "N",
				   status[payload->payload_allocation_status],
				   (*name != 0) ? name : "Unknown");
		}
	}

	seq_printf(m, "\n*** DPCD Info ***\n");
	mutex_lock(&mgr->lock);
	if (mgr->mst_primary) {
		u8 buf[DP_PAYLOAD_TABLE_SIZE];
		int ret;

		if (drm_dp_read_dpcd_caps(mgr->aux, buf) < 0) {
			seq_printf(m, "dpcd read failed\n");
			goto out;
		}
		seq_printf(m, "dpcd: %*ph\n", DP_RECEIVER_CAP_SIZE, buf);

		ret = drm_dp_dpcd_read(mgr->aux, DP_FAUX_CAP, buf, 2);
		if (ret != 2) {
			seq_printf(m, "faux/mst read failed\n");
			goto out;
		}
		seq_printf(m, "faux/mst: %*ph\n", 2, buf);

		ret = drm_dp_dpcd_read(mgr->aux, DP_MSTM_CTRL, buf, 1);
		if (ret != 1) {
			seq_printf(m, "mst ctrl read failed\n");
			goto out;
		}
		seq_printf(m, "mst ctrl: %*ph\n", 1, buf);

		/* dump the standard OUI branch header */
		ret = drm_dp_dpcd_read(mgr->aux, DP_BRANCH_OUI, buf, DP_BRANCH_OUI_HEADER_SIZE);
		if (ret != DP_BRANCH_OUI_HEADER_SIZE) {
			seq_printf(m, "branch oui read failed\n");
			goto out;
		}
		seq_printf(m, "branch oui: %*phN devid: ", 3, buf);

		for (i = 0x3; i < 0x8 && buf[i]; i++)
			seq_printf(m, "%c", buf[i]);
		seq_printf(m, " revision: hw: %x.%x sw: %x.%x\n",
			   buf[0x9] >> 4, buf[0x9] & 0xf, buf[0xa], buf[0xb]);
		if (dump_dp_payload_table(mgr, buf))
			seq_printf(m, "payload table: %*ph\n", DP_PAYLOAD_TABLE_SIZE, buf);
	}

out:
	mutex_unlock(&mgr->lock);
	drm_modeset_unlock(&mgr->base.lock);
}
EXPORT_SYMBOL(drm_dp_mst_dump_topology);

static void drm_dp_tx_work(struct work_struct *work)
{
	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, tx_work);

	mutex_lock(&mgr->qlock);
	if (!list_empty(&mgr->tx_msg_downq))
		process_single_down_tx_qlock(mgr);
	mutex_unlock(&mgr->qlock);
}

static inline void
drm_dp_delayed_destroy_port(struct drm_dp_mst_port *port)
{
	drm_dp_port_set_pdt(port, DP_PEER_DEVICE_NONE, port->mcs);

	if (port->connector) {
		drm_connector_unregister(port->connector);
		drm_connector_put(port->connector);
	}

	drm_dp_mst_put_port_malloc(port);
}

static inline void
drm_dp_delayed_destroy_mstb(struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	struct drm_dp_mst_port *port, *port_tmp;
	struct drm_dp_sideband_msg_tx *txmsg, *txmsg_tmp;
	bool wake_tx = false;

	mutex_lock(&mgr->lock);
	list_for_each_entry_safe(port, port_tmp, &mstb->ports, next) {
		list_del(&port->next);
		drm_dp_mst_topology_put_port(port);
	}
	mutex_unlock(&mgr->lock);

	/* drop any tx slot msg */
	mutex_lock(&mstb->mgr->qlock);
	list_for_each_entry_safe(txmsg, txmsg_tmp, &mgr->tx_msg_downq, next) {
		if (txmsg->dst != mstb)
			continue;

		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
		list_del(&txmsg->next);
		wake_tx = true;
	}
	mutex_unlock(&mstb->mgr->qlock);

	if (wake_tx)
		wake_up_all(&mstb->mgr->tx_waitq);

	drm_dp_mst_put_mstb_malloc(mstb);
}

static void drm_dp_delayed_destroy_work(struct work_struct *work)
{
	struct drm_dp_mst_topology_mgr *mgr =
		container_of(work, struct drm_dp_mst_topology_mgr,
			     delayed_destroy_work);
	bool send_hotplug = false, go_again;

	/*
	 * Not a regular list traverse as we have to drop the destroy
	 * connector lock before destroying the mstb/port, to avoid AB->BA
	 * ordering between this lock and the config mutex.
	 */
	do {
		go_again = false;

		for (;;) {
			struct drm_dp_mst_branch *mstb;

			mutex_lock(&mgr->delayed_destroy_lock);
			mstb = list_first_entry_or_null(&mgr->destroy_branch_device_list,
							struct drm_dp_mst_branch,
							destroy_next);
			if (mstb)
				list_del(&mstb->destroy_next);
			mutex_unlock(&mgr->delayed_destroy_lock);

			if (!mstb)
				break;

			drm_dp_delayed_destroy_mstb(mstb);
			go_again = true;
		}

		for (;;) {
			struct drm_dp_mst_port *port;

			mutex_lock(&mgr->delayed_destroy_lock);
			port = list_first_entry_or_null(&mgr->destroy_port_list,
							struct drm_dp_mst_port,
							next);
			if (port)
				list_del(&port->next);
			mutex_unlock(&mgr->delayed_destroy_lock);

			if (!port)
				break;

			drm_dp_delayed_destroy_port(port);
			send_hotplug = true;
			go_again = true;
		}
	} while (go_again);

	if (send_hotplug)
		drm_kms_helper_hotplug_event(mgr->dev);
}

static struct drm_private_state *
drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
{
	struct drm_dp_mst_topology_state *state, *old_state =
		to_dp_mst_topology_state(obj->state);
	struct drm_dp_mst_atomic_payload *pos, *payload;

	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
	if (!state)
		return NULL;

	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);

	INIT_LIST_HEAD(&state->payloads);
	state->commit_deps = NULL;
	state->num_commit_deps = 0;
	state->pending_crtc_mask = 0;

	list_for_each_entry(pos, &old_state->payloads, next) {
		/* Prune leftover freed timeslot allocations */
		if (pos->delete)
			continue;

		payload = kmemdup(pos, sizeof(*payload), GFP_KERNEL);
		if (!payload)
			goto fail;

		drm_dp_mst_get_port_malloc(payload->port);
		list_add(&payload->next, &state->payloads);
	}

	return &state->base;

fail:
	list_for_each_entry_safe(pos, payload, &state->payloads, next) {
		drm_dp_mst_put_port_malloc(pos->port);
		kfree(pos);
	}
	kfree(state);

	return NULL;
}

static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
				     struct drm_private_state *state)
{
	struct drm_dp_mst_topology_state *mst_state =
		to_dp_mst_topology_state(state);
	struct drm_dp_mst_atomic_payload *pos, *tmp;
	int i;

	list_for_each_entry_safe(pos, tmp, &mst_state->payloads, next) {
		/* We only keep references to ports with active payloads */
		if (!pos->delete)
			drm_dp_mst_put_port_malloc(pos->port);
		kfree(pos);
	}

	for (i = 0; i < mst_state->num_commit_deps; i++)
		drm_crtc_commit_put(mst_state->commit_deps[i]);

	kfree(mst_state->commit_deps);
	kfree(mst_state);
}

static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
						 struct drm_dp_mst_branch *branch)
{
	while (port->parent) {
		if (port->parent == branch)
			return true;

		if (port->parent->port_parent)
			port = port->parent->port_parent;
		else
			break;
	}
	return false;
}

static bool
drm_dp_mst_port_downstream_of_parent_locked(struct drm_dp_mst_topology_mgr *mgr,
					    struct drm_dp_mst_port *port,
					    struct drm_dp_mst_port *parent)
{
	if (!mgr->mst_primary)
		return false;

	port = drm_dp_mst_topology_get_port_validated_locked(mgr->mst_primary,
							     port);
	if (!port)
		return false;

	if (!parent)
		return true;

	parent = drm_dp_mst_topology_get_port_validated_locked(mgr->mst_primary,
							       parent);
	if (!parent)
		return false;

	if (!parent->mstb)
		return false;

	return drm_dp_mst_port_downstream_of_branch(port, parent->mstb);
}

/**
 * drm_dp_mst_port_downstream_of_parent - check if a port is downstream of a parent port
 * @mgr: MST topology manager
 * @port: the port being looked up
 * @parent: the parent port
 *
 * The function returns %true if @port is downstream of @parent. If @parent is
 * %NULL - denoting the root port - the function returns %true if @port is in
 * @mgr's topology.
 */
bool
drm_dp_mst_port_downstream_of_parent(struct drm_dp_mst_topology_mgr *mgr,
				     struct drm_dp_mst_port *port,
				     struct drm_dp_mst_port *parent)
{
	bool ret;

	mutex_lock(&mgr->lock);
	ret = drm_dp_mst_port_downstream_of_parent_locked(mgr, port, parent);
	mutex_unlock(&mgr->lock);

	return ret;
}
EXPORT_SYMBOL(drm_dp_mst_port_downstream_of_parent);

static int
drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
				      struct drm_dp_mst_topology_state *state,
				      struct drm_dp_mst_port **failing_port);

static int
drm_dp_mst_atomic_check_mstb_bw_limit(struct drm_dp_mst_branch *mstb,
				      struct drm_dp_mst_topology_state *state,
				      struct drm_dp_mst_port **failing_port)
{
	struct drm_dp_mst_atomic_payload *payload;
	struct drm_dp_mst_port *port;
	int pbn_used = 0, ret;
	bool found = false;

	/* Check that we have at least one port in our state that's downstream
	 * of this branch, otherwise we can skip this branch
	 */
	list_for_each_entry(payload, &state->payloads, next) {
		if (!payload->pbn ||
		    !drm_dp_mst_port_downstream_of_branch(payload->port, mstb))
			continue;

		found = true;
		break;
	}
	if (!found)
		return 0;

	if (mstb->port_parent)
		drm_dbg_atomic(mstb->mgr->dev,
			       "[MSTB:%p] [MST PORT:%p] Checking bandwidth limits on [MSTB:%p]\n",
			       mstb->port_parent->parent, mstb->port_parent, mstb);
	else
		drm_dbg_atomic(mstb->mgr->dev, "[MSTB:%p] Checking bandwidth limits\n", mstb);

	list_for_each_entry(port, &mstb->ports, next) {
		ret = drm_dp_mst_atomic_check_port_bw_limit(port, state, failing_port);
		if (ret < 0)
			return ret;

		pbn_used += ret;
	}

	return pbn_used;
}

static int
drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
				      struct drm_dp_mst_topology_state *state,
				      struct drm_dp_mst_port **failing_port)
{
	struct drm_dp_mst_atomic_payload *payload;
	int pbn_used = 0;

	if (port->pdt == DP_PEER_DEVICE_NONE)
		return 0;

	if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
		payload = drm_atomic_get_mst_payload_state(state, port);
		if (!payload)
			return 0;

		/*
		 * This could happen if the sink deasserted its HPD line, but
		 * the branch device still reports it as attached (PDT != NONE).
		 */
		if (!port->full_pbn) {
			drm_dbg_atomic(port->mgr->dev,
				       "[MSTB:%p] [MST PORT:%p] no BW available for the port\n",
				       port->parent, port);
			*failing_port = port;
			return -EINVAL;
		}

		pbn_used = payload->pbn;
	} else {
		pbn_used = drm_dp_mst_atomic_check_mstb_bw_limit(port->mstb,
								 state,
								 failing_port);
		if (pbn_used <= 0)
			return pbn_used;
	}

	if (pbn_used > port->full_pbn) {
		drm_dbg_atomic(port->mgr->dev,
			       "[MSTB:%p] [MST PORT:%p] required PBN of %d exceeds port limit of %d\n",
			       port->parent, port, pbn_used, port->full_pbn);
		*failing_port = port;
		return -ENOSPC;
	}

	drm_dbg_atomic(port->mgr->dev, "[MSTB:%p] [MST PORT:%p] uses %d out of %d PBN\n",
		       port->parent, port, pbn_used, port->full_pbn);

	return pbn_used;
}

static inline int
drm_dp_mst_atomic_check_payload_alloc_limits(struct drm_dp_mst_topology_mgr *mgr,
					     struct drm_dp_mst_topology_state *mst_state)
{
	struct drm_dp_mst_atomic_payload *payload;
	int avail_slots = mst_state->total_avail_slots, payload_count = 0;

	list_for_each_entry(payload, &mst_state->payloads, next) {
		/* Releasing payloads is always OK-even if the port is gone */
		if (payload->delete) {
			drm_dbg_atomic(mgr->dev, "[MST PORT:%p] releases all time slots\n",
				       payload->port);
			continue;
		}

		drm_dbg_atomic(mgr->dev, "[MST PORT:%p] requires %d time slots\n",
			       payload->port, payload->time_slots);

		avail_slots -= payload->time_slots;
		if (avail_slots < 0) {
			drm_dbg_atomic(mgr->dev,
				       "[MST PORT:%p] not enough time slots in mst state %p (avail=%d)\n",
				       payload->port, mst_state, avail_slots + payload->time_slots);
			return -ENOSPC;
		}

		if (++payload_count > mgr->max_payloads) {
			drm_dbg_atomic(mgr->dev,
				       "[MST MGR:%p] state %p has too many payloads (max=%d)\n",
				       mgr, mst_state, mgr->max_payloads);
			return -EINVAL;
		}

		/* Assign a VCPI */
		if (!payload->vcpi) {
			payload->vcpi = ffz(mst_state->payload_mask) + 1;
			drm_dbg_atomic(mgr->dev, "[MST PORT:%p] assigned VCPI #%d\n",
				       payload->port, payload->vcpi);
			mst_state->payload_mask |= BIT(payload->vcpi - 1);
		}
	}

	if (!payload_count)
		mst_state->pbn_div.full = dfixed_const(0);

	drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p TU pbn_div=%d avail=%d used=%d\n",
		       mgr, mst_state, dfixed_trunc(mst_state->pbn_div), avail_slots,
		       mst_state->total_avail_slots - avail_slots);

	return 0;
}

/**
 * drm_dp_mst_add_affected_dsc_crtcs
 * @state: Pointer to the new struct drm_dp_mst_topology_state
 * @mgr: MST topology manager
 *
 * Whenever there is a change in mst topology
 * DSC configuration would have to be recalculated
 * therefore we need to trigger modeset on all affected
 * CRTCs in that topology
 *
 * See also:
 * drm_dp_mst_atomic_enable_dsc()
 */
int drm_dp_mst_add_affected_dsc_crtcs(struct drm_atomic_state *state, struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_mst_topology_state *mst_state;
	struct drm_dp_mst_atomic_payload *pos;
	struct drm_connector *connector;
	struct drm_connector_state *conn_state;
	struct drm_crtc *crtc;
	struct drm_crtc_state *crtc_state;

	mst_state = drm_atomic_get_mst_topology_state(state, mgr);

	if (IS_ERR(mst_state))
		return PTR_ERR(mst_state);

	list_for_each_entry(pos, &mst_state->payloads, next) {

		connector = pos->port->connector;

		if (!connector)
			return -EINVAL;

		conn_state = drm_atomic_get_connector_state(state, connector);

		if (IS_ERR(conn_state))
			return PTR_ERR(conn_state);

		crtc = conn_state->crtc;

		if (!crtc)
			continue;

		if (!drm_dp_mst_dsc_aux_for_port(pos->port))
			continue;

		crtc_state = drm_atomic_get_crtc_state(mst_state->base.state, crtc);

		if (IS_ERR(crtc_state))
			return PTR_ERR(crtc_state);

		drm_dbg_atomic(mgr->dev, "[MST MGR:%p] Setting mode_changed flag on CRTC %p\n",
			       mgr, crtc);

		crtc_state->mode_changed = true;
	}
	return 0;
}
EXPORT_SYMBOL(drm_dp_mst_add_affected_dsc_crtcs);

/**
 * drm_dp_mst_atomic_enable_dsc - Set DSC Enable Flag to On/Off
 * @state: Pointer to the new drm_atomic_state
 * @port: Pointer to the affected MST Port
 * @pbn: Newly recalculated bw required for link with DSC enabled
 * @enable: Boolean flag to enable or disable DSC on the port
 *
 * This function enables DSC on the given Port
 * by recalculating its vcpi from pbn provided
 * and sets dsc_enable flag to keep track of which
 * ports have DSC enabled
 *
 */
int drm_dp_mst_atomic_enable_dsc(struct drm_atomic_state *state,
				 struct drm_dp_mst_port *port,
				 int pbn, bool enable)
{
	struct drm_dp_mst_topology_state *mst_state;
	struct drm_dp_mst_atomic_payload *payload;
	int time_slots = 0;

	mst_state = drm_atomic_get_mst_topology_state(state, port->mgr);
	if (IS_ERR(mst_state))
		return PTR_ERR(mst_state);

	payload = drm_atomic_get_mst_payload_state(mst_state, port);
	if (!payload) {
		drm_dbg_atomic(state->dev,
			       "[MST PORT:%p] Couldn't find payload in mst state %p\n",
			       port, mst_state);
		return -EINVAL;
	}

	if (payload->dsc_enabled == enable) {
		drm_dbg_atomic(state->dev,
			       "[MST PORT:%p] DSC flag is already set to %d, returning %d time slots\n",
			       port, enable, payload->time_slots);
		time_slots = payload->time_slots;
	}

	if (enable) {
		time_slots = drm_dp_atomic_find_time_slots(state, port->mgr, port, pbn);
		drm_dbg_atomic(state->dev,
			       "[MST PORT:%p] Enabling DSC flag, reallocating %d time slots on the port\n",
			       port, time_slots);
		if (time_slots < 0)
			return -EINVAL;
	}

	payload->dsc_enabled = enable;

	return time_slots;
}
EXPORT_SYMBOL(drm_dp_mst_atomic_enable_dsc);

/**
 * drm_dp_mst_atomic_check_mgr - Check the atomic state of an MST topology manager
 * @state: The global atomic state
 * @mgr: Manager to check
 * @mst_state: The MST atomic state for @mgr
 * @failing_port: Returns the port with a BW limitation
 *
 * Checks the given MST manager's topology state for an atomic update to ensure
 * that it's valid. This includes checking whether there's enough bandwidth to
 * support the new timeslot allocations in the atomic update.
 *
 * Any atomic drivers supporting DP MST must make sure to call this or
 * the drm_dp_mst_atomic_check() function after checking the rest of their state
 * in their &drm_mode_config_funcs.atomic_check() callback.
 *
 * See also:
 * drm_dp_mst_atomic_check()
 * drm_dp_atomic_find_time_slots()
 * drm_dp_atomic_release_time_slots()
 *
 * Returns:
 *   - 0 if the new state is valid
 *   - %-ENOSPC, if the new state is invalid, because of BW limitation
 *         @failing_port is set to:
 *
 *         - The non-root port where a BW limit check failed
 *           with all the ports downstream of @failing_port passing
 *           the BW limit check.
 *           The returned port pointer is valid until at least
 *           one payload downstream of it exists.
 *         - %NULL if the BW limit check failed at the root port
 *           with all the ports downstream of the root port passing
 *           the BW limit check.
 *
 *   - %-EINVAL, if the new state is invalid, because the root port has
 *     too many payloads.
 */
int drm_dp_mst_atomic_check_mgr(struct drm_atomic_state *state,
				struct drm_dp_mst_topology_mgr *mgr,
				struct drm_dp_mst_topology_state *mst_state,
				struct drm_dp_mst_port **failing_port)
{
	int ret;

	*failing_port = NULL;

	if (!mgr->mst_state)
		return 0;

	mutex_lock(&mgr->lock);
	ret = drm_dp_mst_atomic_check_mstb_bw_limit(mgr->mst_primary,
						    mst_state,
						    failing_port);
	mutex_unlock(&mgr->lock);

	if (ret < 0)
		return ret;

	return drm_dp_mst_atomic_check_payload_alloc_limits(mgr, mst_state);
}
EXPORT_SYMBOL(drm_dp_mst_atomic_check_mgr);

/**
 * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
 * atomic update is valid
 * @state: Pointer to the new &struct drm_dp_mst_topology_state
 *
 * Checks the given topology state for an atomic update to ensure that it's
 * valid, calling drm_dp_mst_atomic_check_mgr() for all MST manager in the
 * atomic state. This includes checking whether there's enough bandwidth to
 * support the new timeslot allocations in the atomic update.
 *
 * Any atomic drivers supporting DP MST must make sure to call this after
 * checking the rest of their state in their
 * &drm_mode_config_funcs.atomic_check() callback.
 *
 * See also:
 * drm_dp_mst_atomic_check_mgr()
 * drm_dp_atomic_find_time_slots()
 * drm_dp_atomic_release_time_slots()
 *
 * Returns:
 *
 * 0 if the new state is valid, negative error code otherwise.
 */
int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
{
	struct drm_dp_mst_topology_mgr *mgr;
	struct drm_dp_mst_topology_state *mst_state;
	int i, ret = 0;

	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
		struct drm_dp_mst_port *tmp_port;

		ret = drm_dp_mst_atomic_check_mgr(state, mgr, mst_state, &tmp_port);
		if (ret)
			break;
	}

	return ret;
}
EXPORT_SYMBOL(drm_dp_mst_atomic_check);

const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
	.atomic_destroy_state = drm_dp_mst_destroy_state,
};
EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);

/**
 * drm_atomic_get_mst_topology_state: get MST topology state
 * @state: global atomic state
 * @mgr: MST topology manager, also the private object in this case
 *
 * This function wraps drm_atomic_get_priv_obj_state() passing in the MST atomic
 * state vtable so that the private object state returned is that of a MST
 * topology object.
 *
 * RETURNS:
 *
 * The MST topology state or error pointer.
 */
struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
								    struct drm_dp_mst_topology_mgr *mgr)
{
	return to_dp_mst_topology_state(drm_atomic_get_private_obj_state(state, &mgr->base));
}
EXPORT_SYMBOL(drm_atomic_get_mst_topology_state);

/**
 * drm_atomic_get_old_mst_topology_state: get old MST topology state in atomic state, if any
 * @state: global atomic state
 * @mgr: MST topology manager, also the private object in this case
 *
 * This function wraps drm_atomic_get_old_private_obj_state() passing in the MST atomic
 * state vtable so that the private object state returned is that of a MST
 * topology object.
 *
 * Returns:
 *
 * The old MST topology state, or NULL if there's no topology state for this MST mgr
 * in the global atomic state
 */
struct drm_dp_mst_topology_state *
drm_atomic_get_old_mst_topology_state(struct drm_atomic_state *state,
				      struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_private_state *old_priv_state =
		drm_atomic_get_old_private_obj_state(state, &mgr->base);

	return old_priv_state ? to_dp_mst_topology_state(old_priv_state) : NULL;
}
EXPORT_SYMBOL(drm_atomic_get_old_mst_topology_state);

/**
 * drm_atomic_get_new_mst_topology_state: get new MST topology state in atomic state, if any
 * @state: global atomic state
 * @mgr: MST topology manager, also the private object in this case
 *
 * This function wraps drm_atomic_get_new_private_obj_state() passing in the MST atomic
 * state vtable so that the private object state returned is that of a MST
 * topology object.
 *
 * Returns:
 *
 * The new MST topology state, or NULL if there's no topology state for this MST mgr
 * in the global atomic state
 */
struct drm_dp_mst_topology_state *
drm_atomic_get_new_mst_topology_state(struct drm_atomic_state *state,
				      struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_private_state *new_priv_state =
		drm_atomic_get_new_private_obj_state(state, &mgr->base);

	return new_priv_state ? to_dp_mst_topology_state(new_priv_state) : NULL;
}
EXPORT_SYMBOL(drm_atomic_get_new_mst_topology_state);

/**
 * drm_dp_mst_topology_mgr_init - initialise a topology manager
 * @mgr: manager struct to initialise
 * @dev: device providing this structure - for i2c addition.
 * @aux: DP helper aux channel to talk to this device
 * @max_dpcd_transaction_bytes: hw specific DPCD transaction limit
 * @max_payloads: maximum number of payloads this GPU can source
 * @conn_base_id: the connector object ID the MST device is connected to.
 *
 * Return 0 for success, or negative error code on failure
 */
int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_device *dev, struct drm_dp_aux *aux,
				 int max_dpcd_transaction_bytes, int max_payloads,
				 int conn_base_id)
{
	struct drm_dp_mst_topology_state *mst_state;

	mutex_init(&mgr->lock);
	mutex_init(&mgr->qlock);
	mutex_init(&mgr->delayed_destroy_lock);
	mutex_init(&mgr->up_req_lock);
	mutex_init(&mgr->probe_lock);
#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
	mutex_init(&mgr->topology_ref_history_lock);
	stack_depot_init();
#endif
	INIT_LIST_HEAD(&mgr->tx_msg_downq);
	INIT_LIST_HEAD(&mgr->destroy_port_list);
	INIT_LIST_HEAD(&mgr->destroy_branch_device_list);
	INIT_LIST_HEAD(&mgr->up_req_list);

	/*
	 * delayed_destroy_work will be queued on a dedicated WQ, so that any
	 * requeuing will be also flushed when deiniting the topology manager.
	 */
	mgr->delayed_destroy_wq = alloc_ordered_workqueue("drm_dp_mst_wq", 0);
	if (mgr->delayed_destroy_wq == NULL)
		return -ENOMEM;

	INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work);
	INIT_WORK(&mgr->tx_work, drm_dp_tx_work);
	INIT_WORK(&mgr->delayed_destroy_work, drm_dp_delayed_destroy_work);
	INIT_WORK(&mgr->up_req_work, drm_dp_mst_up_req_work);
	init_waitqueue_head(&mgr->tx_waitq);
	mgr->dev = dev;
	mgr->aux = aux;
	mgr->max_dpcd_transaction_bytes = max_dpcd_transaction_bytes;
	mgr->max_payloads = max_payloads;
	mgr->conn_base_id = conn_base_id;

	mst_state = kzalloc(sizeof(*mst_state), GFP_KERNEL);
	if (mst_state == NULL)
		return -ENOMEM;

	mst_state->total_avail_slots = 63;
	mst_state->start_slot = 1;

	mst_state->mgr = mgr;
	INIT_LIST_HEAD(&mst_state->payloads);

	drm_atomic_private_obj_init(dev, &mgr->base,
				    &mst_state->base,
				    &drm_dp_mst_topology_state_funcs);

	return 0;
}
EXPORT_SYMBOL(drm_dp_mst_topology_mgr_init);

/**
 * drm_dp_mst_topology_mgr_destroy() - destroy topology manager.
 * @mgr: manager to destroy
 */
void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
{
	drm_dp_mst_topology_mgr_set_mst(mgr, false);
	flush_work(&mgr->work);
	/* The following will also drain any requeued work on the WQ. */
	if (mgr->delayed_destroy_wq) {
		destroy_workqueue(mgr->delayed_destroy_wq);
		mgr->delayed_destroy_wq = NULL;
	}
	mgr->dev = NULL;
	mgr->aux = NULL;
	drm_atomic_private_obj_fini(&mgr->base);
	mgr->funcs = NULL;

	mutex_destroy(&mgr->delayed_destroy_lock);
	mutex_destroy(&mgr->qlock);
	mutex_destroy(&mgr->lock);
	mutex_destroy(&mgr->up_req_lock);
	mutex_destroy(&mgr->probe_lock);
#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
	mutex_destroy(&mgr->topology_ref_history_lock);
#endif
}
EXPORT_SYMBOL(drm_dp_mst_topology_mgr_destroy);

static bool remote_i2c_read_ok(const struct i2c_msg msgs[], int num)
{
	int i;

	if (num - 1 > DP_REMOTE_I2C_READ_MAX_TRANSACTIONS)
		return false;

	for (i = 0; i < num - 1; i++) {
		if (msgs[i].flags & I2C_M_RD ||
		    msgs[i].len > 0xff)
			return false;
	}

	return msgs[num - 1].flags & I2C_M_RD &&
		msgs[num - 1].len <= 0xff;
}

static bool remote_i2c_write_ok(const struct i2c_msg msgs[], int num)
{
	int i;

	for (i = 0; i < num - 1; i++) {
		if (msgs[i].flags & I2C_M_RD || !(msgs[i].flags & I2C_M_STOP) ||
		    msgs[i].len > 0xff)
			return false;
	}

	return !(msgs[num - 1].flags & I2C_M_RD) && msgs[num - 1].len <= 0xff;
}

static int drm_dp_mst_i2c_read(struct drm_dp_mst_branch *mstb,
			       struct drm_dp_mst_port *port,
			       struct i2c_msg *msgs, int num)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	unsigned int i;
	struct drm_dp_sideband_msg_req_body msg;
	struct drm_dp_sideband_msg_tx *txmsg = NULL;
	int ret;

	memset(&msg, 0, sizeof(msg));
	msg.req_type = DP_REMOTE_I2C_READ;
	msg.u.i2c_read.num_transactions = num - 1;
	msg.u.i2c_read.port_number = port->port_num;
	for (i = 0; i < num - 1; i++) {
		msg.u.i2c_read.transactions[i].i2c_dev_id = msgs[i].addr;
		msg.u.i2c_read.transactions[i].num_bytes = msgs[i].len;
		msg.u.i2c_read.transactions[i].bytes = msgs[i].buf;
		msg.u.i2c_read.transactions[i].no_stop_bit = !(msgs[i].flags & I2C_M_STOP);
	}
	msg.u.i2c_read.read_i2c_device_id = msgs[num - 1].addr;
	msg.u.i2c_read.num_bytes_read = msgs[num - 1].len;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		ret = -ENOMEM;
		goto out;
	}

	txmsg->dst = mstb;
	drm_dp_encode_sideband_req(&msg, txmsg);

	drm_dp_queue_down_tx(mgr, txmsg);

	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
	if (ret > 0) {

		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
			ret = -EREMOTEIO;
			goto out;
		}
		if (txmsg->reply.u.remote_i2c_read_ack.num_bytes != msgs[num - 1].len) {
			ret = -EIO;
			goto out;
		}
		memcpy(msgs[num - 1].buf, txmsg->reply.u.remote_i2c_read_ack.bytes, msgs[num - 1].len);
		ret = num;
	}
out:
	kfree(txmsg);
	return ret;
}

static int drm_dp_mst_i2c_write(struct drm_dp_mst_branch *mstb,
				struct drm_dp_mst_port *port,
				struct i2c_msg *msgs, int num)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	unsigned int i;
	struct drm_dp_sideband_msg_req_body msg;
	struct drm_dp_sideband_msg_tx *txmsg = NULL;
	int ret;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
	if (!txmsg) {
		ret = -ENOMEM;
		goto out;
	}
	for (i = 0; i < num; i++) {
		memset(&msg, 0, sizeof(msg));
		msg.req_type = DP_REMOTE_I2C_WRITE;
		msg.u.i2c_write.port_number = port->port_num;
		msg.u.i2c_write.write_i2c_device_id = msgs[i].addr;
		msg.u.i2c_write.num_bytes = msgs[i].len;
		msg.u.i2c_write.bytes = msgs[i].buf;

		memset(txmsg, 0, sizeof(*txmsg));
		txmsg->dst = mstb;

		drm_dp_encode_sideband_req(&msg, txmsg);
		drm_dp_queue_down_tx(mgr, txmsg);

		ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
		if (ret > 0) {
			if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
				ret = -EREMOTEIO;
				goto out;
			}
		} else {
			goto out;
		}
	}
	ret = num;
out:
	kfree(txmsg);
	return ret;
}

/* I2C device */
static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter,
			       struct i2c_msg *msgs, int num)
{
	struct drm_dp_aux *aux = adapter->algo_data;
	struct drm_dp_mst_port *port =
		container_of(aux, struct drm_dp_mst_port, aux);
	struct drm_dp_mst_branch *mstb;
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	int ret;

	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
	if (!mstb)
		return -EREMOTEIO;

	if (remote_i2c_read_ok(msgs, num)) {
		ret = drm_dp_mst_i2c_read(mstb, port, msgs, num);
	} else if (remote_i2c_write_ok(msgs, num)) {
		ret = drm_dp_mst_i2c_write(mstb, port, msgs, num);
	} else {
		drm_dbg_kms(mgr->dev, "Unsupported I2C transaction for MST device\n");
		ret = -EIO;
	}

	drm_dp_mst_topology_put_mstb(mstb);
	return ret;
}

static u32 drm_dp_mst_i2c_functionality(struct i2c_adapter *adapter)
{
	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
	       I2C_FUNC_SMBUS_READ_BLOCK_DATA |
	       I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
	       I2C_FUNC_10BIT_ADDR;
}

static const struct i2c_algorithm drm_dp_mst_i2c_algo = {
	.functionality = drm_dp_mst_i2c_functionality,
	.master_xfer = drm_dp_mst_i2c_xfer,
};

/**
 * drm_dp_mst_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
 * @port: The port to add the I2C bus on
 *
 * Returns 0 on success or a negative error code on failure.
 */
static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
{
	struct drm_dp_aux *aux = &port->aux;
	struct device *parent_dev = port->mgr->dev->dev;

	aux->ddc.algo = &drm_dp_mst_i2c_algo;
	aux->ddc.algo_data = aux;
	aux->ddc.retries = 3;

	aux->ddc.owner = THIS_MODULE;
	/* FIXME: set the kdev of the port's connector as parent */
	aux->ddc.dev.parent = parent_dev;
	aux->ddc.dev.of_node = parent_dev->of_node;

	strscpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev),
		sizeof(aux->ddc.name));

	return i2c_add_adapter(&aux->ddc);
}

/**
 * drm_dp_mst_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
 * @port: The port to remove the I2C bus from
 */
static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port)
{
	i2c_del_adapter(&port->aux.ddc);
}

/**
 * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
 * @port: The port to check
 *
 * A single physical MST hub object can be represented in the topology
 * by multiple branches, with virtual ports between those branches.
 *
 * As of DP1.4, An MST hub with internal (virtual) ports must expose
 * certain DPCD registers over those ports. See sections 2.6.1.1.1
 * and 2.6.1.1.2 of Display Port specification v1.4 for details.
 *
 * May acquire mgr->lock
 *
 * Returns:
 * true if the port is a virtual DP peer device, false otherwise
 */
static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_port *downstream_port;

	if (!port || port->dpcd_rev < DP_DPCD_REV_14)
		return false;

	/* Virtual DP Sink (Internal Display Panel) */
	if (port->port_num >= 8)
		return true;

	/* DP-to-HDMI Protocol Converter */
	if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
	    !port->mcs &&
	    port->ldps)
		return true;

	/* DP-to-DP */
	mutex_lock(&port->mgr->lock);
	if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
	    port->mstb &&
	    port->mstb->num_ports == 2) {
		list_for_each_entry(downstream_port, &port->mstb->ports, next) {
			if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
			    !downstream_port->input) {
				mutex_unlock(&port->mgr->lock);
				return true;
			}
		}
	}
	mutex_unlock(&port->mgr->lock);

	return false;
}

/**
 * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
 * @port: The port to check. A leaf of the MST tree with an attached display.
 *
 * Depending on the situation, DSC may be enabled via the endpoint aux,
 * the immediately upstream aux, or the connector's physical aux.
 *
 * This is both the correct aux to read DSC_CAPABILITY and the
 * correct aux to write DSC_ENABLED.
 *
 * This operation can be expensive (up to four aux reads), so
 * the caller should cache the return.
 *
 * Returns:
 * NULL if DSC cannot be enabled on this port, otherwise the aux device
 */
struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_port *immediate_upstream_port;
	struct drm_dp_aux *immediate_upstream_aux;
	struct drm_dp_mst_port *fec_port;
	struct drm_dp_desc desc = {};
	u8 endpoint_fec;
	u8 endpoint_dsc;

	if (!port)
		return NULL;

	if (port->parent->port_parent)
		immediate_upstream_port = port->parent->port_parent;
	else
		immediate_upstream_port = NULL;

	fec_port = immediate_upstream_port;
	while (fec_port) {
		/*
		 * Each physical link (i.e. not a virtual port) between the
		 * output and the primary device must support FEC
		 */
		if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
		    !fec_port->fec_capable)
			return NULL;

		fec_port = fec_port->parent->port_parent;
	}

	/* DP-to-DP peer device */
	if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
		u8 upstream_dsc;

		if (drm_dp_dpcd_read(&port->aux,
				     DP_DSC_SUPPORT, &endpoint_dsc, 1) != 1)
			return NULL;
		if (drm_dp_dpcd_read(&port->aux,
				     DP_FEC_CAPABILITY, &endpoint_fec, 1) != 1)
			return NULL;
		if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
				     DP_DSC_SUPPORT, &upstream_dsc, 1) != 1)
			return NULL;

		/* Enpoint decompression with DP-to-DP peer device */
		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
		    (endpoint_fec & DP_FEC_CAPABLE) &&
		    (upstream_dsc & DP_DSC_PASSTHROUGH_IS_SUPPORTED)) {
			port->passthrough_aux = &immediate_upstream_port->aux;
			return &port->aux;
		}

		/* Virtual DPCD decompression with DP-to-DP peer device */
		return &immediate_upstream_port->aux;
	}

	/* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
	if (drm_dp_mst_is_virtual_dpcd(port))
		return &port->aux;

	/*
	 * Synaptics quirk
	 * Applies to ports for which:
	 * - Physical aux has Synaptics OUI
	 * - DPv1.4 or higher
	 * - Port is on primary branch device
	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
	 */
	if (immediate_upstream_port)
		immediate_upstream_aux = &immediate_upstream_port->aux;
	else
		immediate_upstream_aux = port->mgr->aux;

	if (drm_dp_read_desc(immediate_upstream_aux, &desc, true))
		return NULL;

	if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD)) {
		u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];

		if (drm_dp_read_dpcd_caps(immediate_upstream_aux, dpcd_ext) < 0)
			return NULL;

		if (dpcd_ext[DP_DPCD_REV] >= DP_DPCD_REV_14 &&
		    ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT) &&
		    ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_TYPE_MASK)
		     != DP_DWN_STRM_PORT_TYPE_ANALOG)))
			return immediate_upstream_aux;
	}

	/*
	 * The check below verifies if the MST sink
	 * connected to the GPU is capable of DSC -
	 * therefore the endpoint needs to be
	 * both DSC and FEC capable.
	 */
	if (drm_dp_dpcd_read(&port->aux,
	   DP_DSC_SUPPORT, &endpoint_dsc, 1) != 1)
		return NULL;
	if (drm_dp_dpcd_read(&port->aux,
	   DP_FEC_CAPABILITY, &endpoint_fec, 1) != 1)
		return NULL;
	if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
	   (endpoint_fec & DP_FEC_CAPABLE))
		return &port->aux;

	return NULL;
}
EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);