xref: /linux/drivers/net/dsa/ks8995.c (revision 4f38da1f027ea2c9f01bb71daa7a299c191b6940)

// SPDX-License-Identifier: GPL-2.0
/*
 * SPI driver for Micrel/Kendin KS8995M and KSZ8864RMN ethernet switches
 *
 * Copyright (C) 2008 Gabor Juhos <juhosg at openwrt.org>
 * Copyright (C) 2025 Linus Walleij <linus.walleij@linaro.org>
 *
 * This file was based on: drivers/spi/at25.c
 *     Copyright (C) 2006 David Brownell
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bits.h>
#include <linux/if_bridge.h>
#include <linux/if_vlan.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>
#include <linux/spi/spi.h>
#include <net/dsa.h>

#define DRV_VERSION		"0.1.1"
#define DRV_DESC		"Micrel KS8995 Ethernet switch SPI driver"

/* ------------------------------------------------------------------------ */

#define KS8995_REG_ID0		0x00    /* Chip ID0 */
#define KS8995_REG_ID1		0x01    /* Chip ID1 */

#define KS8995_REG_GC0		0x02    /* Global Control 0 */

#define KS8995_GC0_P5_PHY	BIT(3)	/* Port 5 PHY enabled */

#define KS8995_REG_GC1		0x03    /* Global Control 1 */
#define KS8995_REG_GC2		0x04    /* Global Control 2 */

#define KS8995_GC2_HUGE		BIT(2)	/* Huge packet support */
#define KS8995_GC2_LEGAL	BIT(1)	/* Legal size override */

#define KS8995_REG_GC3		0x05    /* Global Control 3 */
#define KS8995_REG_GC4		0x06    /* Global Control 4 */

#define KS8995_GC4_10BT		BIT(4)	/* Force switch to 10Mbit */
#define KS8995_GC4_MII_FLOW	BIT(5)	/* MII full-duplex flow control enable */
#define KS8995_GC4_MII_HD	BIT(6)	/* MII half-duplex mode enable */

#define KS8995_REG_GC5		0x07    /* Global Control 5 */
#define KS8995_REG_GC6		0x08    /* Global Control 6 */
#define KS8995_REG_GC7		0x09    /* Global Control 7 */
#define KS8995_REG_GC8		0x0a    /* Global Control 8 */
#define KS8995_REG_GC9		0x0b    /* Global Control 9 */

#define KS8995_GC9_SPECIAL	BIT(0)	/* Special tagging mode (DSA) */

/* In DSA the ports 1-4 are numbered 0-3 and the CPU port is port 4 */
#define KS8995_REG_PC(p, r)	(0x10 + (0x10 * (p)) + (r)) /* Port Control */
#define KS8995_REG_PS(p, r)	(0x1e + (0x10 * (p)) + (r)) /* Port Status */

#define KS8995_REG_PC0		0x00    /* Port Control 0 */
#define KS8995_REG_PC1		0x01    /* Port Control 1 */
#define KS8995_REG_PC2		0x02    /* Port Control 2 */
#define KS8995_REG_PC3		0x03    /* Port Control 3 */
#define KS8995_REG_PC4		0x04    /* Port Control 4 */
#define KS8995_REG_PC5		0x05    /* Port Control 5 */
#define KS8995_REG_PC6		0x06    /* Port Control 6 */
#define KS8995_REG_PC7		0x07    /* Port Control 7 */
#define KS8995_REG_PC8		0x08    /* Port Control 8 */
#define KS8995_REG_PC9		0x09    /* Port Control 9 */
#define KS8995_REG_PC10		0x0a    /* Port Control 10 */
#define KS8995_REG_PC11		0x0b    /* Port Control 11 */
#define KS8995_REG_PC12		0x0c    /* Port Control 12 */
#define KS8995_REG_PC13		0x0d    /* Port Control 13 */

#define KS8995_PC0_TAG_INS	BIT(2)	/* Enable tag insertion on port */
#define KS8995_PC0_TAG_REM	BIT(1)	/* Enable tag removal on port */
#define KS8995_PC0_PRIO_EN	BIT(0)	/* Enable priority handling */

#define KS8995_PC2_TXEN		BIT(2)	/* Enable TX on port */
#define KS8995_PC2_RXEN		BIT(1)	/* Enable RX on port */
#define KS8995_PC2_LEARN_DIS	BIT(0)	/* Disable learning on port */

#define KS8995_PC13_TXDIS	BIT(6)	/* Disable transmitter */
#define KS8995_PC13_PWDN	BIT(3)	/* Power down */

#define KS8995_REG_TPC0		0x60    /* TOS Priority Control 0 */
#define KS8995_REG_TPC1		0x61    /* TOS Priority Control 1 */
#define KS8995_REG_TPC2		0x62    /* TOS Priority Control 2 */
#define KS8995_REG_TPC3		0x63    /* TOS Priority Control 3 */
#define KS8995_REG_TPC4		0x64    /* TOS Priority Control 4 */
#define KS8995_REG_TPC5		0x65    /* TOS Priority Control 5 */
#define KS8995_REG_TPC6		0x66    /* TOS Priority Control 6 */
#define KS8995_REG_TPC7		0x67    /* TOS Priority Control 7 */

#define KS8995_REG_MAC0		0x68    /* MAC address 0 */
#define KS8995_REG_MAC1		0x69    /* MAC address 1 */
#define KS8995_REG_MAC2		0x6a    /* MAC address 2 */
#define KS8995_REG_MAC3		0x6b    /* MAC address 3 */
#define KS8995_REG_MAC4		0x6c    /* MAC address 4 */
#define KS8995_REG_MAC5		0x6d    /* MAC address 5 */

#define KS8995_REG_IAC0		0x6e    /* Indirect Access Control 0 */
#define KS8995_REG_IAC1		0x6f    /* Indirect Access Control 0 */
#define KS8995_REG_IAD7		0x70    /* Indirect Access Data 7 */
#define KS8995_REG_IAD6		0x71    /* Indirect Access Data 6 */
#define KS8995_REG_IAD5		0x72    /* Indirect Access Data 5 */
#define KS8995_REG_IAD4		0x73    /* Indirect Access Data 4 */
#define KS8995_REG_IAD3		0x74    /* Indirect Access Data 3 */
#define KS8995_REG_IAD2		0x75    /* Indirect Access Data 2 */
#define KS8995_REG_IAD1		0x76    /* Indirect Access Data 1 */
#define KS8995_REG_IAD0		0x77    /* Indirect Access Data 0 */

#define KSZ8864_REG_ID1		0xfe	/* Chip ID in bit 7 */

#define KS8995_REGS_SIZE	0x80
#define KSZ8864_REGS_SIZE	0x100
#define KSZ8795_REGS_SIZE	0x100

#define ID1_CHIPID_M		0xf
#define ID1_CHIPID_S		4
#define ID1_REVISION_M		0x7
#define ID1_REVISION_S		1
#define ID1_START_SW		1	/* start the switch */

#define FAMILY_KS8995		0x95
#define FAMILY_KSZ8795		0x87
#define CHIPID_M		0
#define KS8995_CHIP_ID		0x00
#define KSZ8864_CHIP_ID		0x01
#define KSZ8795_CHIP_ID		0x09

#define KS8995_CMD_WRITE	0x02U
#define KS8995_CMD_READ		0x03U

#define KS8995_CPU_PORT		4
#define KS8995_NUM_PORTS	5 /* 5 ports including the CPU port */
#define KS8995_RESET_DELAY	10 /* usec */

enum ks8995_chip_variant {
	ks8995,
	ksz8864,
	ksz8795,
	max_variant
};

struct ks8995_chip_params {
	char *name;
	int family_id;
	int chip_id;
	int regs_size;
	int addr_width;
	int addr_shift;
};

static const struct ks8995_chip_params ks8995_chip[] = {
	[ks8995] = {
		.name = "KS8995MA",
		.family_id = FAMILY_KS8995,
		.chip_id = KS8995_CHIP_ID,
		.regs_size = KS8995_REGS_SIZE,
		.addr_width = 8,
		.addr_shift = 0,
	},
	[ksz8864] = {
		.name = "KSZ8864RMN",
		.family_id = FAMILY_KS8995,
		.chip_id = KSZ8864_CHIP_ID,
		.regs_size = KSZ8864_REGS_SIZE,
		.addr_width = 8,
		.addr_shift = 0,
	},
	[ksz8795] = {
		.name = "KSZ8795CLX",
		.family_id = FAMILY_KSZ8795,
		.chip_id = KSZ8795_CHIP_ID,
		.regs_size = KSZ8795_REGS_SIZE,
		.addr_width = 12,
		.addr_shift = 1,
	},
};

struct ks8995_switch {
	struct spi_device	*spi;
	struct device		*dev;
	struct dsa_switch	*ds;
	struct mutex		lock;
	struct gpio_desc	*reset_gpio;
	struct bin_attribute	regs_attr;
	const struct ks8995_chip_params	*chip;
	int			revision_id;
	unsigned int max_mtu[KS8995_NUM_PORTS];
};

static const struct spi_device_id ks8995_id[] = {
	{"ks8995", ks8995},
	{"ksz8864", ksz8864},
	{"ksz8795", ksz8795},
	{ }
};
MODULE_DEVICE_TABLE(spi, ks8995_id);

static const struct of_device_id ks8895_spi_of_match[] = {
	{ .compatible = "micrel,ks8995" },
	{ .compatible = "micrel,ksz8864" },
	{ .compatible = "micrel,ksz8795" },
	{ },
};
MODULE_DEVICE_TABLE(of, ks8895_spi_of_match);

static inline u8 get_chip_id(u8 val)
{
	return (val >> ID1_CHIPID_S) & ID1_CHIPID_M;
}

static inline u8 get_chip_rev(u8 val)
{
	return (val >> ID1_REVISION_S) & ID1_REVISION_M;
}

/* create_spi_cmd - create a chip specific SPI command header
 * @ks: pointer to switch instance
 * @cmd: SPI command for switch
 * @address: register address for command
 *
 * Different chip families use different bit pattern to address the switches
 * registers:
 *
 * KS8995: 8bit command + 8bit address
 * KSZ8795: 3bit command + 12bit address + 1bit TR (?)
 */
static inline __be16 create_spi_cmd(struct ks8995_switch *ks, int cmd,
				    unsigned address)
{
	u16 result = cmd;

	/* make room for address (incl. address shift) */
	result <<= ks->chip->addr_width + ks->chip->addr_shift;
	/* add address */
	result |= address << ks->chip->addr_shift;
	/* SPI protocol needs big endian */
	return cpu_to_be16(result);
}
/* ------------------------------------------------------------------------ */
static int ks8995_read(struct ks8995_switch *ks, char *buf,
		 unsigned offset, size_t count)
{
	__be16 cmd;
	struct spi_transfer t[2];
	struct spi_message m;
	int err;

	cmd = create_spi_cmd(ks, KS8995_CMD_READ, offset);
	spi_message_init(&m);

	memset(&t, 0, sizeof(t));

	t[0].tx_buf = &cmd;
	t[0].len = sizeof(cmd);
	spi_message_add_tail(&t[0], &m);

	t[1].rx_buf = buf;
	t[1].len = count;
	spi_message_add_tail(&t[1], &m);

	mutex_lock(&ks->lock);
	err = spi_sync(ks->spi, &m);
	mutex_unlock(&ks->lock);

	return err ? err : count;
}

static int ks8995_write(struct ks8995_switch *ks, char *buf,
		 unsigned offset, size_t count)
{
	__be16 cmd;
	struct spi_transfer t[2];
	struct spi_message m;
	int err;

	cmd = create_spi_cmd(ks, KS8995_CMD_WRITE, offset);
	spi_message_init(&m);

	memset(&t, 0, sizeof(t));

	t[0].tx_buf = &cmd;
	t[0].len = sizeof(cmd);
	spi_message_add_tail(&t[0], &m);

	t[1].tx_buf = buf;
	t[1].len = count;
	spi_message_add_tail(&t[1], &m);

	mutex_lock(&ks->lock);
	err = spi_sync(ks->spi, &m);
	mutex_unlock(&ks->lock);

	return err ? err : count;
}

static inline int ks8995_read_reg(struct ks8995_switch *ks, u8 addr, u8 *buf)
{
	return ks8995_read(ks, buf, addr, 1) != 1;
}

static inline int ks8995_write_reg(struct ks8995_switch *ks, u8 addr, u8 val)
{
	char buf = val;

	return ks8995_write(ks, &buf, addr, 1) != 1;
}

/* ------------------------------------------------------------------------ */

static int ks8995_stop(struct ks8995_switch *ks)
{
	return ks8995_write_reg(ks, KS8995_REG_ID1, 0);
}

static int ks8995_start(struct ks8995_switch *ks)
{
	return ks8995_write_reg(ks, KS8995_REG_ID1, 1);
}

static int ks8995_reset(struct ks8995_switch *ks)
{
	int err;

	err = ks8995_stop(ks);
	if (err)
		return err;

	udelay(KS8995_RESET_DELAY);

	return ks8995_start(ks);
}

/* ks8995_get_revision - get chip revision
 * @ks: pointer to switch instance
 *
 * Verify chip family and id and get chip revision.
 */
static int ks8995_get_revision(struct ks8995_switch *ks)
{
	int err;
	u8 id0, id1, ksz8864_id;

	/* read family id */
	err = ks8995_read_reg(ks, KS8995_REG_ID0, &id0);
	if (err) {
		err = -EIO;
		goto err_out;
	}

	/* verify family id */
	if (id0 != ks->chip->family_id) {
		dev_err(&ks->spi->dev, "chip family id mismatch: expected 0x%02x but 0x%02x read\n",
			ks->chip->family_id, id0);
		err = -ENODEV;
		goto err_out;
	}

	switch (ks->chip->family_id) {
	case FAMILY_KS8995:
		/* try reading chip id at CHIP ID1 */
		err = ks8995_read_reg(ks, KS8995_REG_ID1, &id1);
		if (err) {
			err = -EIO;
			goto err_out;
		}

		/* verify chip id */
		if ((get_chip_id(id1) == CHIPID_M) &&
		    (get_chip_id(id1) == ks->chip->chip_id)) {
			/* KS8995MA */
			ks->revision_id = get_chip_rev(id1);
		} else if (get_chip_id(id1) != CHIPID_M) {
			/* KSZ8864RMN */
			err = ks8995_read_reg(ks, KS8995_REG_ID1, &ksz8864_id);
			if (err) {
				err = -EIO;
				goto err_out;
			}

			if ((ksz8864_id & 0x80) &&
			    (ks->chip->chip_id == KSZ8864_CHIP_ID)) {
				ks->revision_id = get_chip_rev(id1);
			}

		} else {
			dev_err(&ks->spi->dev, "unsupported chip id for KS8995 family: 0x%02x\n",
				id1);
			err = -ENODEV;
		}
		break;
	case FAMILY_KSZ8795:
		/* try reading chip id at CHIP ID1 */
		err = ks8995_read_reg(ks, KS8995_REG_ID1, &id1);
		if (err) {
			err = -EIO;
			goto err_out;
		}

		if (get_chip_id(id1) == ks->chip->chip_id) {
			ks->revision_id = get_chip_rev(id1);
		} else {
			dev_err(&ks->spi->dev, "unsupported chip id for KSZ8795 family: 0x%02x\n",
				id1);
			err = -ENODEV;
		}
		break;
	default:
		dev_err(&ks->spi->dev, "unsupported family id: 0x%02x\n", id0);
		err = -ENODEV;
		break;
	}
err_out:
	return err;
}

static int ks8995_check_config(struct ks8995_switch *ks)
{
	int ret;
	u8 val;

	ret = ks8995_read_reg(ks, KS8995_REG_GC0, &val);
	if (ret) {
		dev_err(ks->dev, "failed to read KS8995_REG_GC0\n");
		return ret;
	}

	dev_dbg(ks->dev, "port 5 PHY %senabled\n",
		(val & KS8995_GC0_P5_PHY) ? "" : "not ");

	val |= KS8995_GC0_P5_PHY;
	ret = ks8995_write_reg(ks, KS8995_REG_GC0, val);
	if (ret)
		dev_err(ks->dev, "failed to set KS8995_REG_GC0\n");

	dev_dbg(ks->dev, "set KS8995_REG_GC0 to 0x%02x\n", val);

	return 0;
}

static void
ks8995_mac_config(struct phylink_config *config, unsigned int mode,
		  const struct phylink_link_state *state)
{
}

static void
ks8995_mac_link_up(struct phylink_config *config, struct phy_device *phydev,
		   unsigned int mode, phy_interface_t interface,
		   int speed, int duplex, bool tx_pause, bool rx_pause)
{
	struct dsa_port *dp = dsa_phylink_to_port(config);
	struct ks8995_switch *ks = dp->ds->priv;
	int port = dp->index;
	int ret;
	u8 val;

	/* Allow forcing the mode on the fixed CPU port, no autonegotiation.
	 * We assume autonegotiation works on the PHY-facing ports.
	 */
	if (port != KS8995_CPU_PORT)
		return;

	dev_dbg(ks->dev, "MAC link up on CPU port (%d)\n", port);

	ret = ks8995_read_reg(ks, KS8995_REG_GC4, &val);
	if (ret) {
		dev_err(ks->dev, "failed to read KS8995_REG_GC4\n");
		return;
	}

	/* Conjure port config */
	switch (speed) {
	case SPEED_10:
		dev_dbg(ks->dev, "set switch MII to 100Mbit mode\n");
		val |= KS8995_GC4_10BT;
		break;
	case SPEED_100:
	default:
		dev_dbg(ks->dev, "set switch MII to 100Mbit mode\n");
		val &= ~KS8995_GC4_10BT;
		break;
	}

	if (duplex == DUPLEX_HALF) {
		dev_dbg(ks->dev, "set switch MII to half duplex\n");
		val |= KS8995_GC4_MII_HD;
	} else {
		dev_dbg(ks->dev, "set switch MII to full duplex\n");
		val &= ~KS8995_GC4_MII_HD;
	}

	dev_dbg(ks->dev, "set KS8995_REG_GC4 to %02x\n", val);

	/* Enable the CPU port */
	ret = ks8995_write_reg(ks, KS8995_REG_GC4, val);
	if (ret)
		dev_err(ks->dev, "failed to set KS8995_REG_GC4\n");
}

static void
ks8995_mac_link_down(struct phylink_config *config, unsigned int mode,
		     phy_interface_t interface)
{
	struct dsa_port *dp = dsa_phylink_to_port(config);
	struct ks8995_switch *ks = dp->ds->priv;
	int port = dp->index;

	if (port != KS8995_CPU_PORT)
		return;

	dev_dbg(ks->dev, "MAC link down on CPU port (%d)\n", port);

	/* Disable the CPU port */
}

static const struct phylink_mac_ops ks8995_phylink_mac_ops = {
	.mac_config = ks8995_mac_config,
	.mac_link_up = ks8995_mac_link_up,
	.mac_link_down = ks8995_mac_link_down,
};

static enum
dsa_tag_protocol ks8995_get_tag_protocol(struct dsa_switch *ds,
					 int port,
					 enum dsa_tag_protocol mp)
{
	/* This switch actually uses the 6 byte KS8995 protocol */
	return DSA_TAG_PROTO_NONE;
}

static int ks8995_setup(struct dsa_switch *ds)
{
	return 0;
}

static int ks8995_port_enable(struct dsa_switch *ds, int port,
			      struct phy_device *phy)
{
	struct ks8995_switch *ks = ds->priv;

	dev_dbg(ks->dev, "enable port %d\n", port);

	return 0;
}

static void ks8995_port_disable(struct dsa_switch *ds, int port)
{
	struct ks8995_switch *ks = ds->priv;

	dev_dbg(ks->dev, "disable port %d\n", port);
}

static int ks8995_port_pre_bridge_flags(struct dsa_switch *ds, int port,
					struct switchdev_brport_flags flags,
					struct netlink_ext_ack *extack)
{
	/* We support enabling/disabling learning */
	if (flags.mask & ~(BR_LEARNING))
		return -EINVAL;

	return 0;
}

static int ks8995_port_bridge_flags(struct dsa_switch *ds, int port,
				    struct switchdev_brport_flags flags,
				    struct netlink_ext_ack *extack)
{
	struct ks8995_switch *ks = ds->priv;
	int ret;
	u8 val;

	if (flags.mask & BR_LEARNING) {
		ret = ks8995_read_reg(ks, KS8995_REG_PC(port, KS8995_REG_PC2), &val);
		if (ret) {
			dev_err(ks->dev, "failed to read KS8995_REG_PC2 on port %d\n", port);
			return ret;
		}

		if (flags.val & BR_LEARNING)
			val &= ~KS8995_PC2_LEARN_DIS;
		else
			val |= KS8995_PC2_LEARN_DIS;

		ret = ks8995_write_reg(ks, KS8995_REG_PC(port, KS8995_REG_PC2), val);
		if (ret) {
			dev_err(ks->dev, "failed to write KS8995_REG_PC2 on port %d\n", port);
			return ret;
		}
	}

	return 0;
}

static void ks8995_port_stp_state_set(struct dsa_switch *ds, int port, u8 state)
{
	struct ks8995_switch *ks = ds->priv;
	int ret;
	u8 val;

	ret = ks8995_read_reg(ks, KS8995_REG_PC(port, KS8995_REG_PC2), &val);
	if (ret) {
		dev_err(ks->dev, "failed to read KS8995_REG_PC2 on port %d\n", port);
		return;
	}

	/* Set the bits for the different STP states in accordance with
	 * the datasheet, pages 36-37 "Spanning tree support".
	 */
	switch (state) {
	case BR_STATE_DISABLED:
	case BR_STATE_BLOCKING:
	case BR_STATE_LISTENING:
		val &= ~KS8995_PC2_TXEN;
		val &= ~KS8995_PC2_RXEN;
		val |= KS8995_PC2_LEARN_DIS;
		break;
	case BR_STATE_LEARNING:
		val &= ~KS8995_PC2_TXEN;
		val &= ~KS8995_PC2_RXEN;
		val &= ~KS8995_PC2_LEARN_DIS;
		break;
	case BR_STATE_FORWARDING:
		val |= KS8995_PC2_TXEN;
		val |= KS8995_PC2_RXEN;
		val &= ~KS8995_PC2_LEARN_DIS;
		break;
	default:
		dev_err(ks->dev, "unknown bridge state requested\n");
		return;
	}

	ret = ks8995_write_reg(ks, KS8995_REG_PC(port, KS8995_REG_PC2), val);
	if (ret) {
		dev_err(ks->dev, "failed to write KS8995_REG_PC2 on port %d\n", port);
		return;
	}

	dev_dbg(ks->dev, "set KS8995_REG_PC2 for port %d to %02x\n", port, val);
}

static void ks8995_phylink_get_caps(struct dsa_switch *dsa, int port,
				    struct phylink_config *config)
{
	unsigned long *interfaces = config->supported_interfaces;

	if (port == KS8995_CPU_PORT)
		__set_bit(PHY_INTERFACE_MODE_MII, interfaces);

	if (port <= 3) {
		/* Internal PHYs */
		__set_bit(PHY_INTERFACE_MODE_INTERNAL, interfaces);
		/* phylib default */
		__set_bit(PHY_INTERFACE_MODE_MII, interfaces);
	}

	config->mac_capabilities = MAC_SYM_PAUSE | MAC_10 | MAC_100;
}

/* Huge packet support up to 1916 byte packages "inclusive"
 * which means that tags are included. If the bit is not set
 * it is 1536 bytes "inclusive". We present the length without
 * tags or ethernet headers. The setting affects all ports.
 */
static int ks8995_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
{
	struct ks8995_switch *ks = ds->priv;
	unsigned int max_mtu;
	int ret;
	u8 val;
	int i;

	ks->max_mtu[port] = new_mtu;

	/* Roof out the MTU for the entire switch to the greatest
	 * common denominator: the biggest set for any one port will
	 * be the biggest MTU for the switch.
	 */
	max_mtu = ETH_DATA_LEN;
	for (i = 0; i < KS8995_NUM_PORTS; i++) {
		if (ks->max_mtu[i] > max_mtu)
			max_mtu = ks->max_mtu[i];
	}

	/* Translate to layer 2 size.
	 * Add ethernet and (possible) VLAN headers, and checksum to the size.
	 * For ETH_DATA_LEN (1500 bytes) this will add up to 1522 bytes.
	 */
	max_mtu += VLAN_ETH_HLEN;
	max_mtu += ETH_FCS_LEN;

	ret = ks8995_read_reg(ks, KS8995_REG_GC2, &val);
	if (ret) {
		dev_err(ks->dev, "failed to read KS8995_REG_GC2\n");
		return ret;
	}

	if (max_mtu <= 1522) {
		val &= ~KS8995_GC2_HUGE;
		val &= ~KS8995_GC2_LEGAL;
	} else if (max_mtu > 1522 && max_mtu <= 1536) {
		/* This accepts packets up to 1536 bytes */
		val &= ~KS8995_GC2_HUGE;
		val |= KS8995_GC2_LEGAL;
	} else {
		/* This accepts packets up to 1916 bytes */
		val |= KS8995_GC2_HUGE;
		val |= KS8995_GC2_LEGAL;
	}

	dev_dbg(ks->dev, "new max MTU %d bytes (inclusive)\n", max_mtu);

	ret = ks8995_write_reg(ks, KS8995_REG_GC2, val);
	if (ret)
		dev_err(ks->dev, "failed to set KS8995_REG_GC2\n");

	return ret;
}

static int ks8995_get_max_mtu(struct dsa_switch *ds, int port)
{
	return 1916 - ETH_HLEN - ETH_FCS_LEN;
}

static const struct dsa_switch_ops ks8995_ds_ops = {
	.get_tag_protocol = ks8995_get_tag_protocol,
	.setup = ks8995_setup,
	.port_pre_bridge_flags = ks8995_port_pre_bridge_flags,
	.port_bridge_flags = ks8995_port_bridge_flags,
	.port_enable = ks8995_port_enable,
	.port_disable = ks8995_port_disable,
	.port_stp_state_set = ks8995_port_stp_state_set,
	.port_change_mtu = ks8995_change_mtu,
	.port_max_mtu = ks8995_get_max_mtu,
	.phylink_get_caps = ks8995_phylink_get_caps,
};

/* ------------------------------------------------------------------------ */
static int ks8995_probe(struct spi_device *spi)
{
	struct ks8995_switch *ks;
	int err;
	int variant = spi_get_device_id(spi)->driver_data;

	if (variant >= max_variant) {
		dev_err(&spi->dev, "bad chip variant %d\n", variant);
		return -ENODEV;
	}

	ks = devm_kzalloc(&spi->dev, sizeof(*ks), GFP_KERNEL);
	if (!ks)
		return -ENOMEM;

	mutex_init(&ks->lock);
	ks->spi = spi;
	ks->dev = &spi->dev;
	ks->chip = &ks8995_chip[variant];

	ks->reset_gpio = devm_gpiod_get_optional(&spi->dev, "reset",
						 GPIOD_OUT_HIGH);
	err = PTR_ERR_OR_ZERO(ks->reset_gpio);
	if (err) {
		dev_err(&spi->dev,
			"failed to get reset gpio: %d\n", err);
		return err;
	}

	err = gpiod_set_consumer_name(ks->reset_gpio, "switch-reset");
	if (err)
		return err;

	if (ks->reset_gpio) {
		/*
		 * If a reset line was obtained, wait for 100us after
		 * de-asserting RESET before accessing any registers, see
		 * the KS8995MA datasheet, page 44.
		 */
		gpiod_set_value_cansleep(ks->reset_gpio, 0);
		udelay(100);
	}

	spi_set_drvdata(spi, ks);

	spi->mode = SPI_MODE_0;
	spi->bits_per_word = 8;
	err = spi_setup(spi);
	if (err) {
		dev_err(&spi->dev, "spi_setup failed, err=%d\n", err);
		return err;
	}

	err = ks8995_get_revision(ks);
	if (err)
		return err;

	err = ks8995_reset(ks);
	if (err)
		return err;

	dev_info(&spi->dev, "%s device found, Chip ID:%x, Revision:%x\n",
		 ks->chip->name, ks->chip->chip_id, ks->revision_id);

	err = ks8995_check_config(ks);
	if (err)
		return err;

	ks->ds = devm_kzalloc(&spi->dev, sizeof(*ks->ds), GFP_KERNEL);
	if (!ks->ds)
		return -ENOMEM;

	ks->ds->dev = &spi->dev;
	ks->ds->num_ports = KS8995_NUM_PORTS;
	ks->ds->ops = &ks8995_ds_ops;
	ks->ds->phylink_mac_ops = &ks8995_phylink_mac_ops;
	ks->ds->priv = ks;

	err = dsa_register_switch(ks->ds);
	if (err)
		return dev_err_probe(&spi->dev, err,
				     "unable to register DSA switch\n");

	return 0;
}

static void ks8995_remove(struct spi_device *spi)
{
	struct ks8995_switch *ks = spi_get_drvdata(spi);

	dsa_unregister_switch(ks->ds);
	/* assert reset */
	gpiod_set_value_cansleep(ks->reset_gpio, 1);
}

/* ------------------------------------------------------------------------ */
static struct spi_driver ks8995_driver = {
	.driver = {
		.name	    = "spi-ks8995",
		.of_match_table = ks8895_spi_of_match,
	},
	.probe	  = ks8995_probe,
	.remove	  = ks8995_remove,
	.id_table = ks8995_id,
};

module_spi_driver(ks8995_driver);

MODULE_DESCRIPTION(DRV_DESC);
MODULE_VERSION(DRV_VERSION);
MODULE_AUTHOR("Gabor Juhos <juhosg at openwrt.org>");
MODULE_LICENSE("GPL v2");