xref: /linux/drivers/net/can/grcan.c (revision e5c86679d5e864947a52fb31e45a425dea3e7fa9)

/*
 * Socket CAN driver for Aeroflex Gaisler GRCAN and GRHCAN.
 *
 * 2012 (c) Aeroflex Gaisler AB
 *
 * This driver supports GRCAN and GRHCAN CAN controllers available in the GRLIB
 * VHDL IP core library.
 *
 * Full documentation of the GRCAN core can be found here:
 * http://www.gaisler.com/products/grlib/grip.pdf
 *
 * See "Documentation/devicetree/bindings/net/can/grcan.txt" for information on
 * open firmware properties.
 *
 * See "Documentation/ABI/testing/sysfs-class-net-grcan" for information on the
 * sysfs interface.
 *
 * See "Documentation/admin-guide/kernel-parameters.rst" for information on the module
 * parameters.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * Contributors: Andreas Larsson <andreas@gaisler.com>
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/netdevice.h>
#include <linux/delay.h>
#include <linux/io.h>
#include <linux/can/dev.h>
#include <linux/spinlock.h>
#include <linux/of_platform.h>
#include <linux/of_irq.h>

#include <linux/dma-mapping.h>

#define DRV_NAME	"grcan"

#define GRCAN_NAPI_WEIGHT	32

#define GRCAN_RESERVE_SIZE(slot1, slot2) (((slot2) - (slot1)) / 4 - 1)

struct grcan_registers {
	u32 conf;	/* 0x00 */
	u32 stat;	/* 0x04 */
	u32 ctrl;	/* 0x08 */
	u32 __reserved1[GRCAN_RESERVE_SIZE(0x08, 0x18)];
	u32 smask;	/* 0x18 - CanMASK */
	u32 scode;	/* 0x1c - CanCODE */
	u32 __reserved2[GRCAN_RESERVE_SIZE(0x1c, 0x100)];
	u32 pimsr;	/* 0x100 */
	u32 pimr;	/* 0x104 */
	u32 pisr;	/* 0x108 */
	u32 pir;	/* 0x10C */
	u32 imr;	/* 0x110 */
	u32 picr;	/* 0x114 */
	u32 __reserved3[GRCAN_RESERVE_SIZE(0x114, 0x200)];
	u32 txctrl;	/* 0x200 */
	u32 txaddr;	/* 0x204 */
	u32 txsize;	/* 0x208 */
	u32 txwr;	/* 0x20C */
	u32 txrd;	/* 0x210 */
	u32 txirq;	/* 0x214 */
	u32 __reserved4[GRCAN_RESERVE_SIZE(0x214, 0x300)];
	u32 rxctrl;	/* 0x300 */
	u32 rxaddr;	/* 0x304 */
	u32 rxsize;	/* 0x308 */
	u32 rxwr;	/* 0x30C */
	u32 rxrd;	/* 0x310 */
	u32 rxirq;	/* 0x314 */
	u32 rxmask;	/* 0x318 */
	u32 rxcode;	/* 0x31C */
};

#define GRCAN_CONF_ABORT	0x00000001
#define GRCAN_CONF_ENABLE0	0x00000002
#define GRCAN_CONF_ENABLE1	0x00000004
#define GRCAN_CONF_SELECT	0x00000008
#define GRCAN_CONF_SILENT	0x00000010
#define GRCAN_CONF_SAM		0x00000020 /* Available in some hardware */
#define GRCAN_CONF_BPR		0x00000300 /* Note: not BRP */
#define GRCAN_CONF_RSJ		0x00007000
#define GRCAN_CONF_PS1		0x00f00000
#define GRCAN_CONF_PS2		0x000f0000
#define GRCAN_CONF_SCALER	0xff000000
#define GRCAN_CONF_OPERATION						\
	(GRCAN_CONF_ABORT | GRCAN_CONF_ENABLE0 | GRCAN_CONF_ENABLE1	\
	 | GRCAN_CONF_SELECT | GRCAN_CONF_SILENT | GRCAN_CONF_SAM)
#define GRCAN_CONF_TIMING						\
	(GRCAN_CONF_BPR | GRCAN_CONF_RSJ | GRCAN_CONF_PS1		\
	 | GRCAN_CONF_PS2 | GRCAN_CONF_SCALER)

#define GRCAN_CONF_RSJ_MIN	1
#define GRCAN_CONF_RSJ_MAX	4
#define GRCAN_CONF_PS1_MIN	1
#define GRCAN_CONF_PS1_MAX	15
#define GRCAN_CONF_PS2_MIN	2
#define GRCAN_CONF_PS2_MAX	8
#define GRCAN_CONF_SCALER_MIN	0
#define GRCAN_CONF_SCALER_MAX	255
#define GRCAN_CONF_SCALER_INC	1

#define GRCAN_CONF_BPR_BIT	8
#define GRCAN_CONF_RSJ_BIT	12
#define GRCAN_CONF_PS1_BIT	20
#define GRCAN_CONF_PS2_BIT	16
#define GRCAN_CONF_SCALER_BIT	24

#define GRCAN_STAT_PASS		0x000001
#define GRCAN_STAT_OFF		0x000002
#define GRCAN_STAT_OR		0x000004
#define GRCAN_STAT_AHBERR	0x000008
#define GRCAN_STAT_ACTIVE	0x000010
#define GRCAN_STAT_RXERRCNT	0x00ff00
#define GRCAN_STAT_TXERRCNT	0xff0000

#define GRCAN_STAT_ERRCTR_RELATED	(GRCAN_STAT_PASS | GRCAN_STAT_OFF)

#define GRCAN_STAT_RXERRCNT_BIT	8
#define GRCAN_STAT_TXERRCNT_BIT	16

#define GRCAN_STAT_ERRCNT_WARNING_LIMIT	96
#define GRCAN_STAT_ERRCNT_PASSIVE_LIMIT	127

#define GRCAN_CTRL_RESET	0x2
#define GRCAN_CTRL_ENABLE	0x1

#define GRCAN_TXCTRL_ENABLE	0x1
#define GRCAN_TXCTRL_ONGOING	0x2
#define GRCAN_TXCTRL_SINGLE	0x4

#define GRCAN_RXCTRL_ENABLE	0x1
#define GRCAN_RXCTRL_ONGOING	0x2

/* Relative offset of IRQ sources to AMBA Plug&Play */
#define GRCAN_IRQIX_IRQ		0
#define GRCAN_IRQIX_TXSYNC	1
#define GRCAN_IRQIX_RXSYNC	2

#define GRCAN_IRQ_PASS		0x00001
#define GRCAN_IRQ_OFF		0x00002
#define GRCAN_IRQ_OR		0x00004
#define GRCAN_IRQ_RXAHBERR	0x00008
#define GRCAN_IRQ_TXAHBERR	0x00010
#define GRCAN_IRQ_RXIRQ		0x00020
#define GRCAN_IRQ_TXIRQ		0x00040
#define GRCAN_IRQ_RXFULL	0x00080
#define GRCAN_IRQ_TXEMPTY	0x00100
#define GRCAN_IRQ_RX		0x00200
#define GRCAN_IRQ_TX		0x00400
#define GRCAN_IRQ_RXSYNC	0x00800
#define GRCAN_IRQ_TXSYNC	0x01000
#define GRCAN_IRQ_RXERRCTR	0x02000
#define GRCAN_IRQ_TXERRCTR	0x04000
#define GRCAN_IRQ_RXMISS	0x08000
#define GRCAN_IRQ_TXLOSS	0x10000

#define GRCAN_IRQ_NONE	0
#define GRCAN_IRQ_ALL							\
	(GRCAN_IRQ_PASS | GRCAN_IRQ_OFF | GRCAN_IRQ_OR			\
	 | GRCAN_IRQ_RXAHBERR | GRCAN_IRQ_TXAHBERR			\
	 | GRCAN_IRQ_RXIRQ | GRCAN_IRQ_TXIRQ				\
	 | GRCAN_IRQ_RXFULL | GRCAN_IRQ_TXEMPTY				\
	 | GRCAN_IRQ_RX | GRCAN_IRQ_TX | GRCAN_IRQ_RXSYNC		\
	 | GRCAN_IRQ_TXSYNC | GRCAN_IRQ_RXERRCTR			\
	 | GRCAN_IRQ_TXERRCTR | GRCAN_IRQ_RXMISS			\
	 | GRCAN_IRQ_TXLOSS)

#define GRCAN_IRQ_ERRCTR_RELATED (GRCAN_IRQ_RXERRCTR | GRCAN_IRQ_TXERRCTR \
				  | GRCAN_IRQ_PASS | GRCAN_IRQ_OFF)
#define GRCAN_IRQ_ERRORS (GRCAN_IRQ_ERRCTR_RELATED | GRCAN_IRQ_OR	\
			  | GRCAN_IRQ_TXAHBERR | GRCAN_IRQ_RXAHBERR	\
			  | GRCAN_IRQ_TXLOSS)
#define GRCAN_IRQ_DEFAULT (GRCAN_IRQ_RX | GRCAN_IRQ_TX | GRCAN_IRQ_ERRORS)

#define GRCAN_MSG_SIZE		16

#define GRCAN_MSG_IDE		0x80000000
#define GRCAN_MSG_RTR		0x40000000
#define GRCAN_MSG_BID		0x1ffc0000
#define GRCAN_MSG_EID		0x1fffffff
#define GRCAN_MSG_IDE_BIT	31
#define GRCAN_MSG_RTR_BIT	30
#define GRCAN_MSG_BID_BIT	18
#define GRCAN_MSG_EID_BIT	0

#define GRCAN_MSG_DLC		0xf0000000
#define GRCAN_MSG_TXERRC	0x00ff0000
#define GRCAN_MSG_RXERRC	0x0000ff00
#define GRCAN_MSG_DLC_BIT	28
#define GRCAN_MSG_TXERRC_BIT	16
#define GRCAN_MSG_RXERRC_BIT	8
#define GRCAN_MSG_AHBERR	0x00000008
#define GRCAN_MSG_OR		0x00000004
#define GRCAN_MSG_OFF		0x00000002
#define GRCAN_MSG_PASS		0x00000001

#define GRCAN_MSG_DATA_SLOT_INDEX(i) (2 + (i) / 4)
#define GRCAN_MSG_DATA_SHIFT(i) ((3 - (i) % 4) * 8)

#define GRCAN_BUFFER_ALIGNMENT		1024
#define GRCAN_DEFAULT_BUFFER_SIZE	1024
#define GRCAN_VALID_TR_SIZE_MASK	0x001fffc0

#define GRCAN_INVALID_BUFFER_SIZE(s)			\
	((s) == 0 || ((s) & ~GRCAN_VALID_TR_SIZE_MASK))

#if GRCAN_INVALID_BUFFER_SIZE(GRCAN_DEFAULT_BUFFER_SIZE)
#error "Invalid default buffer size"
#endif

struct grcan_dma_buffer {
	size_t size;
	void *buf;
	dma_addr_t handle;
};

struct grcan_dma {
	size_t base_size;
	void *base_buf;
	dma_addr_t base_handle;
	struct grcan_dma_buffer tx;
	struct grcan_dma_buffer rx;
};

/* GRCAN configuration parameters */
struct grcan_device_config {
	unsigned short enable0;
	unsigned short enable1;
	unsigned short select;
	unsigned int txsize;
	unsigned int rxsize;
};

#define GRCAN_DEFAULT_DEVICE_CONFIG {				\
		.enable0	= 0,				\
		.enable1	= 0,				\
		.select		= 0,				\
		.txsize		= GRCAN_DEFAULT_BUFFER_SIZE,	\
		.rxsize		= GRCAN_DEFAULT_BUFFER_SIZE,	\
		}

#define GRCAN_TXBUG_SAFE_GRLIB_VERSION	0x4100
#define GRLIB_VERSION_MASK		0xffff

/* GRCAN private data structure */
struct grcan_priv {
	struct can_priv can;	/* must be the first member */
	struct net_device *dev;
	struct napi_struct napi;

	struct grcan_registers __iomem *regs;	/* ioremap'ed registers */
	struct grcan_device_config config;
	struct grcan_dma dma;

	struct sk_buff **echo_skb;	/* We allocate this on our own */
	u8 *txdlc;			/* Length of queued frames */

	/* The echo skb pointer, pointing into echo_skb and indicating which
	 * frames can be echoed back. See the "Notes on the tx cyclic buffer
	 * handling"-comment for grcan_start_xmit for more details.
	 */
	u32 eskbp;

	/* Lock for controlling changes to the netif tx queue state, accesses to
	 * the echo_skb pointer eskbp and for making sure that a running reset
	 * and/or a close of the interface is done without interference from
	 * other parts of the code.
	 *
	 * The echo_skb pointer, eskbp, should only be accessed under this lock
	 * as it can be changed in several places and together with decisions on
	 * whether to wake up the tx queue.
	 *
	 * The tx queue must never be woken up if there is a running reset or
	 * close in progress.
	 *
	 * A running reset (see below on need_txbug_workaround) should never be
	 * done if the interface is closing down and several running resets
	 * should never be scheduled simultaneously.
	 */
	spinlock_t lock;

	/* Whether a workaround is needed due to a bug in older hardware. In
	 * this case, the driver both tries to prevent the bug from being
	 * triggered and recovers, if the bug nevertheless happens, by doing a
	 * running reset. A running reset, resets the device and continues from
	 * where it were without being noticeable from outside the driver (apart
	 * from slight delays).
	 */
	bool need_txbug_workaround;

	/* To trigger initization of running reset and to trigger running reset
	 * respectively in the case of a hanged device due to a txbug.
	 */
	struct timer_list hang_timer;
	struct timer_list rr_timer;

	/* To avoid waking up the netif queue and restarting timers
	 * when a reset is scheduled or when closing of the device is
	 * undergoing
	 */
	bool resetting;
	bool closing;
};

/* Wait time for a short wait for ongoing to clear */
#define GRCAN_SHORTWAIT_USECS	10

/* Limit on the number of transmitted bits of an eff frame according to the CAN
 * specification: 1 bit start of frame, 32 bits arbitration field, 6 bits
 * control field, 8 bytes data field, 16 bits crc field, 2 bits ACK field and 7
 * bits end of frame
 */
#define GRCAN_EFF_FRAME_MAX_BITS	(1+32+6+8*8+16+2+7)

#if defined(__BIG_ENDIAN)
static inline u32 grcan_read_reg(u32 __iomem *reg)
{
	return ioread32be(reg);
}

static inline void grcan_write_reg(u32 __iomem *reg, u32 val)
{
	iowrite32be(val, reg);
}
#else
static inline u32 grcan_read_reg(u32 __iomem *reg)
{
	return ioread32(reg);
}

static inline void grcan_write_reg(u32 __iomem *reg, u32 val)
{
	iowrite32(val, reg);
}
#endif

static inline void grcan_clear_bits(u32 __iomem *reg, u32 mask)
{
	grcan_write_reg(reg, grcan_read_reg(reg) & ~mask);
}

static inline void grcan_set_bits(u32 __iomem *reg, u32 mask)
{
	grcan_write_reg(reg, grcan_read_reg(reg) | mask);
}

static inline u32 grcan_read_bits(u32 __iomem *reg, u32 mask)
{
	return grcan_read_reg(reg) & mask;
}

static inline void grcan_write_bits(u32 __iomem *reg, u32 value, u32 mask)
{
	u32 old = grcan_read_reg(reg);

	grcan_write_reg(reg, (old & ~mask) | (value & mask));
}

/* a and b should both be in [0,size] and a == b == size should not hold */
static inline u32 grcan_ring_add(u32 a, u32 b, u32 size)
{
	u32 sum = a + b;

	if (sum < size)
		return sum;
	else
		return sum - size;
}

/* a and b should both be in [0,size) */
static inline u32 grcan_ring_sub(u32 a, u32 b, u32 size)
{
	return grcan_ring_add(a, size - b, size);
}

/* Available slots for new transmissions */
static inline u32 grcan_txspace(size_t txsize, u32 txwr, u32 eskbp)
{
	u32 slots = txsize / GRCAN_MSG_SIZE - 1;
	u32 used = grcan_ring_sub(txwr, eskbp, txsize) / GRCAN_MSG_SIZE;

	return slots - used;
}

/* Configuration parameters that can be set via module parameters */
static struct grcan_device_config grcan_module_config =
	GRCAN_DEFAULT_DEVICE_CONFIG;

static const struct can_bittiming_const grcan_bittiming_const = {
	.name		= DRV_NAME,
	.tseg1_min	= GRCAN_CONF_PS1_MIN + 1,
	.tseg1_max	= GRCAN_CONF_PS1_MAX + 1,
	.tseg2_min	= GRCAN_CONF_PS2_MIN,
	.tseg2_max	= GRCAN_CONF_PS2_MAX,
	.sjw_max	= GRCAN_CONF_RSJ_MAX,
	.brp_min	= GRCAN_CONF_SCALER_MIN + 1,
	.brp_max	= GRCAN_CONF_SCALER_MAX + 1,
	.brp_inc	= GRCAN_CONF_SCALER_INC,
};

static int grcan_set_bittiming(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct can_bittiming *bt = &priv->can.bittiming;
	u32 timing = 0;
	int bpr, rsj, ps1, ps2, scaler;

	/* Should never happen - function will not be called when
	 * device is up
	 */
	if (grcan_read_bits(&regs->ctrl, GRCAN_CTRL_ENABLE))
		return -EBUSY;

	bpr = 0; /* Note bpr and brp are different concepts */
	rsj = bt->sjw;
	ps1 = (bt->prop_seg + bt->phase_seg1) - 1; /* tseg1 - 1 */
	ps2 = bt->phase_seg2;
	scaler = (bt->brp - 1);
	netdev_dbg(dev, "Request for BPR=%d, RSJ=%d, PS1=%d, PS2=%d, SCALER=%d",
		   bpr, rsj, ps1, ps2, scaler);
	if (!(ps1 > ps2)) {
		netdev_err(dev, "PS1 > PS2 must hold: PS1=%d, PS2=%d\n",
			   ps1, ps2);
		return -EINVAL;
	}
	if (!(ps2 >= rsj)) {
		netdev_err(dev, "PS2 >= RSJ must hold: PS2=%d, RSJ=%d\n",
			   ps2, rsj);
		return -EINVAL;
	}

	timing |= (bpr << GRCAN_CONF_BPR_BIT) & GRCAN_CONF_BPR;
	timing |= (rsj << GRCAN_CONF_RSJ_BIT) & GRCAN_CONF_RSJ;
	timing |= (ps1 << GRCAN_CONF_PS1_BIT) & GRCAN_CONF_PS1;
	timing |= (ps2 << GRCAN_CONF_PS2_BIT) & GRCAN_CONF_PS2;
	timing |= (scaler << GRCAN_CONF_SCALER_BIT) & GRCAN_CONF_SCALER;
	netdev_info(dev, "setting timing=0x%x\n", timing);
	grcan_write_bits(&regs->conf, timing, GRCAN_CONF_TIMING);

	return 0;
}

static int grcan_get_berr_counter(const struct net_device *dev,
				  struct can_berr_counter *bec)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	u32 status = grcan_read_reg(&regs->stat);

	bec->txerr = (status & GRCAN_STAT_TXERRCNT) >> GRCAN_STAT_TXERRCNT_BIT;
	bec->rxerr = (status & GRCAN_STAT_RXERRCNT) >> GRCAN_STAT_RXERRCNT_BIT;
	return 0;
}

static int grcan_poll(struct napi_struct *napi, int budget);

/* Reset device, but keep configuration information */
static void grcan_reset(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	u32 config = grcan_read_reg(&regs->conf);

	grcan_set_bits(&regs->ctrl, GRCAN_CTRL_RESET);
	grcan_write_reg(&regs->conf, config);

	priv->eskbp = grcan_read_reg(&regs->txrd);
	priv->can.state = CAN_STATE_STOPPED;

	/* Turn off hardware filtering - regs->rxcode set to 0 by reset */
	grcan_write_reg(&regs->rxmask, 0);
}

/* stop device without changing any configurations */
static void grcan_stop_hardware(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;

	grcan_write_reg(&regs->imr, GRCAN_IRQ_NONE);
	grcan_clear_bits(&regs->txctrl, GRCAN_TXCTRL_ENABLE);
	grcan_clear_bits(&regs->rxctrl, GRCAN_RXCTRL_ENABLE);
	grcan_clear_bits(&regs->ctrl, GRCAN_CTRL_ENABLE);
}

/* Let priv->eskbp catch up to regs->txrd and echo back the skbs if echo
 * is true and free them otherwise.
 *
 * If budget is >= 0, stop after handling at most budget skbs. Otherwise,
 * continue until priv->eskbp catches up to regs->txrd.
 *
 * priv->lock *must* be held when calling this function
 */
static int catch_up_echo_skb(struct net_device *dev, int budget, bool echo)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	struct net_device_stats *stats = &dev->stats;
	int i, work_done;

	/* Updates to priv->eskbp and wake-ups of the queue needs to
	 * be atomic towards the reads of priv->eskbp and shut-downs
	 * of the queue in grcan_start_xmit.
	 */
	u32 txrd = grcan_read_reg(&regs->txrd);

	for (work_done = 0; work_done < budget || budget < 0; work_done++) {
		if (priv->eskbp == txrd)
			break;
		i = priv->eskbp / GRCAN_MSG_SIZE;
		if (echo) {
			/* Normal echo of messages */
			stats->tx_packets++;
			stats->tx_bytes += priv->txdlc[i];
			priv->txdlc[i] = 0;
			can_get_echo_skb(dev, i);
		} else {
			/* For cleanup of untransmitted messages */
			can_free_echo_skb(dev, i);
		}

		priv->eskbp = grcan_ring_add(priv->eskbp, GRCAN_MSG_SIZE,
					     dma->tx.size);
		txrd = grcan_read_reg(&regs->txrd);
	}
	return work_done;
}

static void grcan_lost_one_shot_frame(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	u32 txrd;
	unsigned long flags;

	spin_lock_irqsave(&priv->lock, flags);

	catch_up_echo_skb(dev, -1, true);

	if (unlikely(grcan_read_bits(&regs->txctrl, GRCAN_TXCTRL_ENABLE))) {
		/* Should never happen */
		netdev_err(dev, "TXCTRL enabled at TXLOSS in one shot mode\n");
	} else {
		/* By the time an GRCAN_IRQ_TXLOSS is generated in
		 * one-shot mode there is no problem in writing
		 * to TXRD even in versions of the hardware in
		 * which GRCAN_TXCTRL_ONGOING is not cleared properly
		 * in one-shot mode.
		 */

		/* Skip message and discard echo-skb */
		txrd = grcan_read_reg(&regs->txrd);
		txrd = grcan_ring_add(txrd, GRCAN_MSG_SIZE, dma->tx.size);
		grcan_write_reg(&regs->txrd, txrd);
		catch_up_echo_skb(dev, -1, false);

		if (!priv->resetting && !priv->closing &&
		    !(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)) {
			netif_wake_queue(dev);
			grcan_set_bits(&regs->txctrl, GRCAN_TXCTRL_ENABLE);
		}
	}

	spin_unlock_irqrestore(&priv->lock, flags);
}

static void grcan_err(struct net_device *dev, u32 sources, u32 status)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	struct net_device_stats *stats = &dev->stats;
	struct can_frame cf;

	/* Zero potential error_frame */
	memset(&cf, 0, sizeof(cf));

	/* Message lost interrupt. This might be due to arbitration error, but
	 * is also triggered when there is no one else on the can bus or when
	 * there is a problem with the hardware interface or the bus itself. As
	 * arbitration errors can not be singled out, no error frames are
	 * generated reporting this event as an arbitration error.
	 */
	if (sources & GRCAN_IRQ_TXLOSS) {
		/* Take care of failed one-shot transmit */
		if (priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT)
			grcan_lost_one_shot_frame(dev);

		/* Stop printing as soon as error passive or bus off is in
		 * effect to limit the amount of txloss debug printouts.
		 */
		if (!(status & GRCAN_STAT_ERRCTR_RELATED)) {
			netdev_dbg(dev, "tx message lost\n");
			stats->tx_errors++;
		}
	}

	/* Conditions dealing with the error counters. There is no interrupt for
	 * error warning, but there are interrupts for increases of the error
	 * counters.
	 */
	if ((sources & GRCAN_IRQ_ERRCTR_RELATED) ||
	    (status & GRCAN_STAT_ERRCTR_RELATED)) {
		enum can_state state = priv->can.state;
		enum can_state oldstate = state;
		u32 txerr = (status & GRCAN_STAT_TXERRCNT)
			>> GRCAN_STAT_TXERRCNT_BIT;
		u32 rxerr = (status & GRCAN_STAT_RXERRCNT)
			>> GRCAN_STAT_RXERRCNT_BIT;

		/* Figure out current state */
		if (status & GRCAN_STAT_OFF) {
			state = CAN_STATE_BUS_OFF;
		} else if (status & GRCAN_STAT_PASS) {
			state = CAN_STATE_ERROR_PASSIVE;
		} else if (txerr >= GRCAN_STAT_ERRCNT_WARNING_LIMIT ||
			   rxerr >= GRCAN_STAT_ERRCNT_WARNING_LIMIT) {
			state = CAN_STATE_ERROR_WARNING;
		} else {
			state = CAN_STATE_ERROR_ACTIVE;
		}

		/* Handle and report state changes */
		if (state != oldstate) {
			switch (state) {
			case CAN_STATE_BUS_OFF:
				netdev_dbg(dev, "bus-off\n");
				netif_carrier_off(dev);
				priv->can.can_stats.bus_off++;

				/* Prevent the hardware from recovering from bus
				 * off on its own if restart is disabled.
				 */
				if (!priv->can.restart_ms)
					grcan_stop_hardware(dev);

				cf.can_id |= CAN_ERR_BUSOFF;
				break;

			case CAN_STATE_ERROR_PASSIVE:
				netdev_dbg(dev, "Error passive condition\n");
				priv->can.can_stats.error_passive++;

				cf.can_id |= CAN_ERR_CRTL;
				if (txerr >= GRCAN_STAT_ERRCNT_PASSIVE_LIMIT)
					cf.data[1] |= CAN_ERR_CRTL_TX_PASSIVE;
				if (rxerr >= GRCAN_STAT_ERRCNT_PASSIVE_LIMIT)
					cf.data[1] |= CAN_ERR_CRTL_RX_PASSIVE;
				break;

			case CAN_STATE_ERROR_WARNING:
				netdev_dbg(dev, "Error warning condition\n");
				priv->can.can_stats.error_warning++;

				cf.can_id |= CAN_ERR_CRTL;
				if (txerr >= GRCAN_STAT_ERRCNT_WARNING_LIMIT)
					cf.data[1] |= CAN_ERR_CRTL_TX_WARNING;
				if (rxerr >= GRCAN_STAT_ERRCNT_WARNING_LIMIT)
					cf.data[1] |= CAN_ERR_CRTL_RX_WARNING;
				break;

			case CAN_STATE_ERROR_ACTIVE:
				netdev_dbg(dev, "Error active condition\n");
				cf.can_id |= CAN_ERR_CRTL;
				break;

			default:
				/* There are no others at this point */
				break;
			}
			cf.data[6] = txerr;
			cf.data[7] = rxerr;
			priv->can.state = state;
		}

		/* Report automatic restarts */
		if (priv->can.restart_ms && oldstate == CAN_STATE_BUS_OFF) {
			unsigned long flags;

			cf.can_id |= CAN_ERR_RESTARTED;
			netdev_dbg(dev, "restarted\n");
			priv->can.can_stats.restarts++;
			netif_carrier_on(dev);

			spin_lock_irqsave(&priv->lock, flags);

			if (!priv->resetting && !priv->closing) {
				u32 txwr = grcan_read_reg(&regs->txwr);

				if (grcan_txspace(dma->tx.size, txwr,
						  priv->eskbp))
					netif_wake_queue(dev);
			}

			spin_unlock_irqrestore(&priv->lock, flags);
		}
	}

	/* Data overrun interrupt */
	if ((sources & GRCAN_IRQ_OR) || (status & GRCAN_STAT_OR)) {
		netdev_dbg(dev, "got data overrun interrupt\n");
		stats->rx_over_errors++;
		stats->rx_errors++;

		cf.can_id |= CAN_ERR_CRTL;
		cf.data[1] |= CAN_ERR_CRTL_RX_OVERFLOW;
	}

	/* AHB bus error interrupts (not CAN bus errors) - shut down the
	 * device.
	 */
	if (sources & (GRCAN_IRQ_TXAHBERR | GRCAN_IRQ_RXAHBERR) ||
	    (status & GRCAN_STAT_AHBERR)) {
		char *txrx = "";
		unsigned long flags;

		if (sources & GRCAN_IRQ_TXAHBERR) {
			txrx = "on tx ";
			stats->tx_errors++;
		} else if (sources & GRCAN_IRQ_RXAHBERR) {
			txrx = "on rx ";
			stats->rx_errors++;
		}
		netdev_err(dev, "Fatal AHB buss error %s- halting device\n",
			   txrx);

		spin_lock_irqsave(&priv->lock, flags);

		/* Prevent anything to be enabled again and halt device */
		priv->closing = true;
		netif_stop_queue(dev);
		grcan_stop_hardware(dev);
		priv->can.state = CAN_STATE_STOPPED;

		spin_unlock_irqrestore(&priv->lock, flags);
	}

	/* Pass on error frame if something to report,
	 * i.e. id contains some information
	 */
	if (cf.can_id) {
		struct can_frame *skb_cf;
		struct sk_buff *skb = alloc_can_err_skb(dev, &skb_cf);

		if (skb == NULL) {
			netdev_dbg(dev, "could not allocate error frame\n");
			return;
		}
		skb_cf->can_id |= cf.can_id;
		memcpy(skb_cf->data, cf.data, sizeof(cf.data));

		netif_rx(skb);
	}
}

static irqreturn_t grcan_interrupt(int irq, void *dev_id)
{
	struct net_device *dev = dev_id;
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	u32 sources, status;

	/* Find out the source */
	sources = grcan_read_reg(&regs->pimsr);
	if (!sources)
		return IRQ_NONE;
	grcan_write_reg(&regs->picr, sources);
	status = grcan_read_reg(&regs->stat);

	/* If we got TX progress, the device has not hanged,
	 * so disable the hang timer
	 */
	if (priv->need_txbug_workaround &&
	    (sources & (GRCAN_IRQ_TX | GRCAN_IRQ_TXLOSS))) {
		del_timer(&priv->hang_timer);
	}

	/* Frame(s) received or transmitted */
	if (sources & (GRCAN_IRQ_TX | GRCAN_IRQ_RX)) {
		/* Disable tx/rx interrupts and schedule poll(). No need for
		 * locking as interference from a running reset at worst leads
		 * to an extra interrupt.
		 */
		grcan_clear_bits(&regs->imr, GRCAN_IRQ_TX | GRCAN_IRQ_RX);
		napi_schedule(&priv->napi);
	}

	/* (Potential) error conditions to take care of */
	if (sources & GRCAN_IRQ_ERRORS)
		grcan_err(dev, sources, status);

	return IRQ_HANDLED;
}

/* Reset device and restart operations from where they were.
 *
 * This assumes that RXCTRL & RXCTRL is properly disabled and that RX
 * is not ONGOING (TX might be stuck in ONGOING due to a harwrware bug
 * for single shot)
 */
static void grcan_running_reset(unsigned long data)
{
	struct net_device *dev = (struct net_device *)data;
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	unsigned long flags;

	/* This temporarily messes with eskbp, so we need to lock
	 * priv->lock
	 */
	spin_lock_irqsave(&priv->lock, flags);

	priv->resetting = false;
	del_timer(&priv->hang_timer);
	del_timer(&priv->rr_timer);

	if (!priv->closing) {
		/* Save and reset - config register preserved by grcan_reset */
		u32 imr = grcan_read_reg(&regs->imr);

		u32 txaddr = grcan_read_reg(&regs->txaddr);
		u32 txsize = grcan_read_reg(&regs->txsize);
		u32 txwr = grcan_read_reg(&regs->txwr);
		u32 txrd = grcan_read_reg(&regs->txrd);
		u32 eskbp = priv->eskbp;

		u32 rxaddr = grcan_read_reg(&regs->rxaddr);
		u32 rxsize = grcan_read_reg(&regs->rxsize);
		u32 rxwr = grcan_read_reg(&regs->rxwr);
		u32 rxrd = grcan_read_reg(&regs->rxrd);

		grcan_reset(dev);

		/* Restore */
		grcan_write_reg(&regs->txaddr, txaddr);
		grcan_write_reg(&regs->txsize, txsize);
		grcan_write_reg(&regs->txwr, txwr);
		grcan_write_reg(&regs->txrd, txrd);
		priv->eskbp = eskbp;

		grcan_write_reg(&regs->rxaddr, rxaddr);
		grcan_write_reg(&regs->rxsize, rxsize);
		grcan_write_reg(&regs->rxwr, rxwr);
		grcan_write_reg(&regs->rxrd, rxrd);

		/* Turn on device again */
		grcan_write_reg(&regs->imr, imr);
		priv->can.state = CAN_STATE_ERROR_ACTIVE;
		grcan_write_reg(&regs->txctrl, GRCAN_TXCTRL_ENABLE
				| (priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT
				   ? GRCAN_TXCTRL_SINGLE : 0));
		grcan_write_reg(&regs->rxctrl, GRCAN_RXCTRL_ENABLE);
		grcan_write_reg(&regs->ctrl, GRCAN_CTRL_ENABLE);

		/* Start queue if there is size and listen-onle mode is not
		 * enabled
		 */
		if (grcan_txspace(priv->dma.tx.size, txwr, priv->eskbp) &&
		    !(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
			netif_wake_queue(dev);
	}

	spin_unlock_irqrestore(&priv->lock, flags);

	netdev_err(dev, "Device reset and restored\n");
}

/* Waiting time in usecs corresponding to the transmission of three maximum
 * sized can frames in the given bitrate (in bits/sec). Waiting for this amount
 * of time makes sure that the can controller have time to finish sending or
 * receiving a frame with a good margin.
 *
 * usecs/sec * number of frames * bits/frame / bits/sec
 */
static inline u32 grcan_ongoing_wait_usecs(__u32 bitrate)
{
	return 1000000 * 3 * GRCAN_EFF_FRAME_MAX_BITS / bitrate;
}

/* Set timer so that it will not fire until after a period in which the can
 * controller have a good margin to finish transmitting a frame unless it has
 * hanged
 */
static inline void grcan_reset_timer(struct timer_list *timer, __u32 bitrate)
{
	u32 wait_jiffies = usecs_to_jiffies(grcan_ongoing_wait_usecs(bitrate));

	mod_timer(timer, jiffies + wait_jiffies);
}

/* Disable channels and schedule a running reset */
static void grcan_initiate_running_reset(unsigned long data)
{
	struct net_device *dev = (struct net_device *)data;
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	unsigned long flags;

	netdev_err(dev, "Device seems hanged - reset scheduled\n");

	spin_lock_irqsave(&priv->lock, flags);

	/* The main body of this function must never be executed again
	 * until after an execution of grcan_running_reset
	 */
	if (!priv->resetting && !priv->closing) {
		priv->resetting = true;
		netif_stop_queue(dev);
		grcan_clear_bits(&regs->txctrl, GRCAN_TXCTRL_ENABLE);
		grcan_clear_bits(&regs->rxctrl, GRCAN_RXCTRL_ENABLE);
		grcan_reset_timer(&priv->rr_timer, priv->can.bittiming.bitrate);
	}

	spin_unlock_irqrestore(&priv->lock, flags);
}

static void grcan_free_dma_buffers(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_dma *dma = &priv->dma;

	dma_free_coherent(&dev->dev, dma->base_size, dma->base_buf,
			  dma->base_handle);
	memset(dma, 0, sizeof(*dma));
}

static int grcan_allocate_dma_buffers(struct net_device *dev,
				      size_t tsize, size_t rsize)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_dma *dma = &priv->dma;
	struct grcan_dma_buffer *large = rsize > tsize ? &dma->rx : &dma->tx;
	struct grcan_dma_buffer *small = rsize > tsize ? &dma->tx : &dma->rx;
	size_t shift;

	/* Need a whole number of GRCAN_BUFFER_ALIGNMENT for the large,
	 * i.e. first buffer
	 */
	size_t maxs = max(tsize, rsize);
	size_t lsize = ALIGN(maxs, GRCAN_BUFFER_ALIGNMENT);

	/* Put the small buffer after that */
	size_t ssize = min(tsize, rsize);

	/* Extra GRCAN_BUFFER_ALIGNMENT to allow for alignment */
	dma->base_size = lsize + ssize + GRCAN_BUFFER_ALIGNMENT;
	dma->base_buf = dma_alloc_coherent(&dev->dev,
					   dma->base_size,
					   &dma->base_handle,
					   GFP_KERNEL);

	if (!dma->base_buf)
		return -ENOMEM;

	dma->tx.size = tsize;
	dma->rx.size = rsize;

	large->handle = ALIGN(dma->base_handle, GRCAN_BUFFER_ALIGNMENT);
	small->handle = large->handle + lsize;
	shift = large->handle - dma->base_handle;

	large->buf = dma->base_buf + shift;
	small->buf = large->buf + lsize;

	return 0;
}

/* priv->lock *must* be held when calling this function */
static int grcan_start(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	u32 confop, txctrl;

	grcan_reset(dev);

	grcan_write_reg(&regs->txaddr, priv->dma.tx.handle);
	grcan_write_reg(&regs->txsize, priv->dma.tx.size);
	/* regs->txwr, regs->txrd and priv->eskbp already set to 0 by reset */

	grcan_write_reg(&regs->rxaddr, priv->dma.rx.handle);
	grcan_write_reg(&regs->rxsize, priv->dma.rx.size);
	/* regs->rxwr and regs->rxrd already set to 0 by reset */

	/* Enable interrupts */
	grcan_read_reg(&regs->pir);
	grcan_write_reg(&regs->imr, GRCAN_IRQ_DEFAULT);

	/* Enable interfaces, channels and device */
	confop = GRCAN_CONF_ABORT
		| (priv->config.enable0 ? GRCAN_CONF_ENABLE0 : 0)
		| (priv->config.enable1 ? GRCAN_CONF_ENABLE1 : 0)
		| (priv->config.select ? GRCAN_CONF_SELECT : 0)
		| (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY ?
		   GRCAN_CONF_SILENT : 0)
		| (priv->can.ctrlmode & CAN_CTRLMODE_3_SAMPLES ?
		   GRCAN_CONF_SAM : 0);
	grcan_write_bits(&regs->conf, confop, GRCAN_CONF_OPERATION);
	txctrl = GRCAN_TXCTRL_ENABLE
		| (priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT
		   ? GRCAN_TXCTRL_SINGLE : 0);
	grcan_write_reg(&regs->txctrl, txctrl);
	grcan_write_reg(&regs->rxctrl, GRCAN_RXCTRL_ENABLE);
	grcan_write_reg(&regs->ctrl, GRCAN_CTRL_ENABLE);

	priv->can.state = CAN_STATE_ERROR_ACTIVE;

	return 0;
}

static int grcan_set_mode(struct net_device *dev, enum can_mode mode)
{
	struct grcan_priv *priv = netdev_priv(dev);
	unsigned long flags;
	int err = 0;

	if (mode == CAN_MODE_START) {
		/* This might be called to restart the device to recover from
		 * bus off errors
		 */
		spin_lock_irqsave(&priv->lock, flags);
		if (priv->closing || priv->resetting) {
			err = -EBUSY;
		} else {
			netdev_info(dev, "Restarting device\n");
			grcan_start(dev);
			if (!(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
				netif_wake_queue(dev);
		}
		spin_unlock_irqrestore(&priv->lock, flags);
		return err;
	}
	return -EOPNOTSUPP;
}

static int grcan_open(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_dma *dma = &priv->dma;
	unsigned long flags;
	int err;

	/* Allocate memory */
	err = grcan_allocate_dma_buffers(dev, priv->config.txsize,
					 priv->config.rxsize);
	if (err) {
		netdev_err(dev, "could not allocate DMA buffers\n");
		return err;
	}

	priv->echo_skb = kzalloc(dma->tx.size * sizeof(*priv->echo_skb),
				 GFP_KERNEL);
	if (!priv->echo_skb) {
		err = -ENOMEM;
		goto exit_free_dma_buffers;
	}
	priv->can.echo_skb_max = dma->tx.size;
	priv->can.echo_skb = priv->echo_skb;

	priv->txdlc = kzalloc(dma->tx.size * sizeof(*priv->txdlc), GFP_KERNEL);
	if (!priv->txdlc) {
		err = -ENOMEM;
		goto exit_free_echo_skb;
	}

	/* Get can device up */
	err = open_candev(dev);
	if (err)
		goto exit_free_txdlc;

	err = request_irq(dev->irq, grcan_interrupt, IRQF_SHARED,
			  dev->name, dev);
	if (err)
		goto exit_close_candev;

	spin_lock_irqsave(&priv->lock, flags);

	napi_enable(&priv->napi);
	grcan_start(dev);
	if (!(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
		netif_start_queue(dev);
	priv->resetting = false;
	priv->closing = false;

	spin_unlock_irqrestore(&priv->lock, flags);

	return 0;

exit_close_candev:
	close_candev(dev);
exit_free_txdlc:
	kfree(priv->txdlc);
exit_free_echo_skb:
	kfree(priv->echo_skb);
exit_free_dma_buffers:
	grcan_free_dma_buffers(dev);
	return err;
}

static int grcan_close(struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	unsigned long flags;

	napi_disable(&priv->napi);

	spin_lock_irqsave(&priv->lock, flags);

	priv->closing = true;
	if (priv->need_txbug_workaround) {
		del_timer_sync(&priv->hang_timer);
		del_timer_sync(&priv->rr_timer);
	}
	netif_stop_queue(dev);
	grcan_stop_hardware(dev);
	priv->can.state = CAN_STATE_STOPPED;

	spin_unlock_irqrestore(&priv->lock, flags);

	free_irq(dev->irq, dev);
	close_candev(dev);

	grcan_free_dma_buffers(dev);
	priv->can.echo_skb_max = 0;
	priv->can.echo_skb = NULL;
	kfree(priv->echo_skb);
	kfree(priv->txdlc);

	return 0;
}

static int grcan_transmit_catch_up(struct net_device *dev, int budget)
{
	struct grcan_priv *priv = netdev_priv(dev);
	unsigned long flags;
	int work_done;

	spin_lock_irqsave(&priv->lock, flags);

	work_done = catch_up_echo_skb(dev, budget, true);
	if (work_done) {
		if (!priv->resetting && !priv->closing &&
		    !(priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
			netif_wake_queue(dev);

		/* With napi we don't get TX interrupts for a while,
		 * so prevent a running reset while catching up
		 */
		if (priv->need_txbug_workaround)
			del_timer(&priv->hang_timer);
	}

	spin_unlock_irqrestore(&priv->lock, flags);

	return work_done;
}

static int grcan_receive(struct net_device *dev, int budget)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	struct net_device_stats *stats = &dev->stats;
	struct can_frame *cf;
	struct sk_buff *skb;
	u32 wr, rd, startrd;
	u32 *slot;
	u32 i, rtr, eff, j, shift;
	int work_done = 0;

	rd = grcan_read_reg(&regs->rxrd);
	startrd = rd;
	for (work_done = 0; work_done < budget; work_done++) {
		/* Check for packet to receive */
		wr = grcan_read_reg(&regs->rxwr);
		if (rd == wr)
			break;

		/* Take care of packet */
		skb = alloc_can_skb(dev, &cf);
		if (skb == NULL) {
			netdev_err(dev,
				   "dropping frame: skb allocation failed\n");
			stats->rx_dropped++;
			continue;
		}

		slot = dma->rx.buf + rd;
		eff = slot[0] & GRCAN_MSG_IDE;
		rtr = slot[0] & GRCAN_MSG_RTR;
		if (eff) {
			cf->can_id = ((slot[0] & GRCAN_MSG_EID)
				      >> GRCAN_MSG_EID_BIT);
			cf->can_id |= CAN_EFF_FLAG;
		} else {
			cf->can_id = ((slot[0] & GRCAN_MSG_BID)
				      >> GRCAN_MSG_BID_BIT);
		}
		cf->can_dlc = get_can_dlc((slot[1] & GRCAN_MSG_DLC)
					  >> GRCAN_MSG_DLC_BIT);
		if (rtr) {
			cf->can_id |= CAN_RTR_FLAG;
		} else {
			for (i = 0; i < cf->can_dlc; i++) {
				j = GRCAN_MSG_DATA_SLOT_INDEX(i);
				shift = GRCAN_MSG_DATA_SHIFT(i);
				cf->data[i] = (u8)(slot[j] >> shift);
			}
		}

		/* Update statistics and read pointer */
		stats->rx_packets++;
		stats->rx_bytes += cf->can_dlc;
		netif_receive_skb(skb);

		rd = grcan_ring_add(rd, GRCAN_MSG_SIZE, dma->rx.size);
	}

	/* Make sure everything is read before allowing hardware to
	 * use the memory
	 */
	mb();

	/* Update read pointer - no need to check for ongoing */
	if (likely(rd != startrd))
		grcan_write_reg(&regs->rxrd, rd);

	return work_done;
}

static int grcan_poll(struct napi_struct *napi, int budget)
{
	struct grcan_priv *priv = container_of(napi, struct grcan_priv, napi);
	struct net_device *dev = priv->dev;
	struct grcan_registers __iomem *regs = priv->regs;
	unsigned long flags;
	int tx_work_done, rx_work_done;
	int rx_budget = budget / 2;
	int tx_budget = budget - rx_budget;

	/* Half of the budget for receiveing messages */
	rx_work_done = grcan_receive(dev, rx_budget);

	/* Half of the budget for transmitting messages as that can trigger echo
	 * frames being received
	 */
	tx_work_done = grcan_transmit_catch_up(dev, tx_budget);

	if (rx_work_done < rx_budget && tx_work_done < tx_budget) {
		napi_complete(napi);

		/* Guarantee no interference with a running reset that otherwise
		 * could turn off interrupts.
		 */
		spin_lock_irqsave(&priv->lock, flags);

		/* Enable tx and rx interrupts again. No need to check
		 * priv->closing as napi_disable in grcan_close is waiting for
		 * scheduled napi calls to finish.
		 */
		grcan_set_bits(&regs->imr, GRCAN_IRQ_TX | GRCAN_IRQ_RX);

		spin_unlock_irqrestore(&priv->lock, flags);
	}

	return rx_work_done + tx_work_done;
}

/* Work tx bug by waiting while for the risky situation to clear. If that fails,
 * drop a frame in one-shot mode or indicate a busy device otherwise.
 *
 * Returns 0 on successful wait. Otherwise it sets *netdev_tx_status to the
 * value that should be returned by grcan_start_xmit when aborting the xmit.
 */
static int grcan_txbug_workaround(struct net_device *dev, struct sk_buff *skb,
				  u32 txwr, u32 oneshotmode,
				  netdev_tx_t *netdev_tx_status)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	int i;
	unsigned long flags;

	/* Wait a while for ongoing to be cleared or read pointer to catch up to
	 * write pointer. The latter is needed due to a bug in older versions of
	 * GRCAN in which ONGOING is not cleared properly one-shot mode when a
	 * transmission fails.
	 */
	for (i = 0; i < GRCAN_SHORTWAIT_USECS; i++) {
		udelay(1);
		if (!grcan_read_bits(&regs->txctrl, GRCAN_TXCTRL_ONGOING) ||
		    grcan_read_reg(&regs->txrd) == txwr) {
			return 0;
		}
	}

	/* Clean up, in case the situation was not resolved */
	spin_lock_irqsave(&priv->lock, flags);
	if (!priv->resetting && !priv->closing) {
		/* Queue might have been stopped earlier in grcan_start_xmit */
		if (grcan_txspace(dma->tx.size, txwr, priv->eskbp))
			netif_wake_queue(dev);
		/* Set a timer to resolve a hanged tx controller */
		if (!timer_pending(&priv->hang_timer))
			grcan_reset_timer(&priv->hang_timer,
					  priv->can.bittiming.bitrate);
	}
	spin_unlock_irqrestore(&priv->lock, flags);

	if (oneshotmode) {
		/* In one-shot mode we should never end up here because
		 * then the interrupt handler increases txrd on TXLOSS,
		 * but it is consistent with one-shot mode to drop the
		 * frame in this case.
		 */
		kfree_skb(skb);
		*netdev_tx_status = NETDEV_TX_OK;
	} else {
		/* In normal mode the socket-can transmission queue get
		 * to keep the frame so that it can be retransmitted
		 * later
		 */
		*netdev_tx_status = NETDEV_TX_BUSY;
	}
	return -EBUSY;
}

/* Notes on the tx cyclic buffer handling:
 *
 * regs->txwr	- the next slot for the driver to put data to be sent
 * regs->txrd	- the next slot for the device to read data
 * priv->eskbp	- the next slot for the driver to call can_put_echo_skb for
 *
 * grcan_start_xmit can enter more messages as long as regs->txwr does
 * not reach priv->eskbp (within 1 message gap)
 *
 * The device sends messages until regs->txrd reaches regs->txwr
 *
 * The interrupt calls handler calls can_put_echo_skb until
 * priv->eskbp reaches regs->txrd
 */
static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
				    struct net_device *dev)
{
	struct grcan_priv *priv = netdev_priv(dev);
	struct grcan_registers __iomem *regs = priv->regs;
	struct grcan_dma *dma = &priv->dma;
	struct can_frame *cf = (struct can_frame *)skb->data;
	u32 id, txwr, txrd, space, txctrl;
	int slotindex;
	u32 *slot;
	u32 i, rtr, eff, dlc, tmp, err;
	int j, shift;
	unsigned long flags;
	u32 oneshotmode = priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT;

	if (can_dropped_invalid_skb(dev, skb))
		return NETDEV_TX_OK;

	/* Trying to transmit in silent mode will generate error interrupts, but
	 * this should never happen - the queue should not have been started.
	 */
	if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
		return NETDEV_TX_BUSY;

	/* Reads of priv->eskbp and shut-downs of the queue needs to
	 * be atomic towards the updates to priv->eskbp and wake-ups
	 * of the queue in the interrupt handler.
	 */
	spin_lock_irqsave(&priv->lock, flags);

	txwr = grcan_read_reg(&regs->txwr);
	space = grcan_txspace(dma->tx.size, txwr, priv->eskbp);

	slotindex = txwr / GRCAN_MSG_SIZE;
	slot = dma->tx.buf + txwr;

	if (unlikely(space == 1))
		netif_stop_queue(dev);

	spin_unlock_irqrestore(&priv->lock, flags);
	/* End of critical section*/

	/* This should never happen. If circular buffer is full, the
	 * netif_stop_queue should have been stopped already.
	 */
	if (unlikely(!space)) {
		netdev_err(dev, "No buffer space, but queue is non-stopped.\n");
		return NETDEV_TX_BUSY;
	}

	/* Convert and write CAN message to DMA buffer */
	eff = cf->can_id & CAN_EFF_FLAG;
	rtr = cf->can_id & CAN_RTR_FLAG;
	id = cf->can_id & (eff ? CAN_EFF_MASK : CAN_SFF_MASK);
	dlc = cf->can_dlc;
	if (eff)
		tmp = (id << GRCAN_MSG_EID_BIT) & GRCAN_MSG_EID;
	else
		tmp = (id << GRCAN_MSG_BID_BIT) & GRCAN_MSG_BID;
	slot[0] = (eff ? GRCAN_MSG_IDE : 0) | (rtr ? GRCAN_MSG_RTR : 0) | tmp;

	slot[1] = ((dlc << GRCAN_MSG_DLC_BIT) & GRCAN_MSG_DLC);
	slot[2] = 0;
	slot[3] = 0;
	for (i = 0; i < dlc; i++) {
		j = GRCAN_MSG_DATA_SLOT_INDEX(i);
		shift = GRCAN_MSG_DATA_SHIFT(i);
		slot[j] |= cf->data[i] << shift;
	}

	/* Checking that channel has not been disabled. These cases
	 * should never happen
	 */
	txctrl = grcan_read_reg(&regs->txctrl);
	if (!(txctrl & GRCAN_TXCTRL_ENABLE))
		netdev_err(dev, "tx channel spuriously disabled\n");

	if (oneshotmode && !(txctrl & GRCAN_TXCTRL_SINGLE))
		netdev_err(dev, "one-shot mode spuriously disabled\n");

	/* Bug workaround for old version of grcan where updating txwr
	 * in the same clock cycle as the controller updates txrd to
	 * the current txwr could hang the can controller
	 */
	if (priv->need_txbug_workaround) {
		txrd = grcan_read_reg(&regs->txrd);
		if (unlikely(grcan_ring_sub(txwr, txrd, dma->tx.size) == 1)) {
			netdev_tx_t txstatus;

			err = grcan_txbug_workaround(dev, skb, txwr,
						     oneshotmode, &txstatus);
			if (err)
				return txstatus;
		}
	}

	/* Prepare skb for echoing. This must be after the bug workaround above
	 * as ownership of the skb is passed on by calling can_put_echo_skb.
	 * Returning NETDEV_TX_BUSY or accessing skb or cf after a call to
	 * can_put_echo_skb would be an error unless other measures are
	 * taken.
	 */
	priv->txdlc[slotindex] = cf->can_dlc; /* Store dlc for statistics */
	can_put_echo_skb(skb, dev, slotindex);

	/* Make sure everything is written before allowing hardware to
	 * read from the memory
	 */
	wmb();

	/* Update write pointer to start transmission */
	grcan_write_reg(&regs->txwr,
			grcan_ring_add(txwr, GRCAN_MSG_SIZE, dma->tx.size));

	return NETDEV_TX_OK;
}

/* ========== Setting up sysfs interface and module parameters ========== */

#define GRCAN_NOT_BOOL(unsigned_val) ((unsigned_val) > 1)

#define GRCAN_MODULE_PARAM(name, mtype, valcheckf, desc)		\
	static void grcan_sanitize_##name(struct platform_device *pd)	\
	{								\
		struct grcan_device_config grcan_default_config		\
			= GRCAN_DEFAULT_DEVICE_CONFIG;			\
		if (valcheckf(grcan_module_config.name)) {		\
			dev_err(&pd->dev,				\
				"Invalid module parameter value for "	\
				#name " - setting default\n");		\
			grcan_module_config.name =			\
				grcan_default_config.name;		\
		}							\
	}								\
	module_param_named(name, grcan_module_config.name,		\
			   mtype, S_IRUGO);				\
	MODULE_PARM_DESC(name, desc)

#define GRCAN_CONFIG_ATTR(name, desc)					\
	static ssize_t grcan_store_##name(struct device *sdev,		\
					  struct device_attribute *att,	\
					  const char *buf,		\
					  size_t count)			\
	{								\
		struct net_device *dev = to_net_dev(sdev);		\
		struct grcan_priv *priv = netdev_priv(dev);		\
		u8 val;							\
		int ret;						\
		if (dev->flags & IFF_UP)				\
			return -EBUSY;					\
		ret = kstrtou8(buf, 0, &val);				\
		if (ret < 0 || val > 1)					\
			return -EINVAL;					\
		priv->config.name = val;				\
		return count;						\
	}								\
	static ssize_t grcan_show_##name(struct device *sdev,		\
					 struct device_attribute *att,	\
					 char *buf)			\
	{								\
		struct net_device *dev = to_net_dev(sdev);		\
		struct grcan_priv *priv = netdev_priv(dev);		\
		return sprintf(buf, "%d\n", priv->config.name);		\
	}								\
	static DEVICE_ATTR(name, S_IRUGO | S_IWUSR,			\
			   grcan_show_##name,				\
			   grcan_store_##name);				\
	GRCAN_MODULE_PARAM(name, ushort, GRCAN_NOT_BOOL, desc)

/* The following configuration options are made available both via module
 * parameters and writable sysfs files. See the chapter about GRCAN in the
 * documentation for the GRLIB VHDL library for further details.
 */
GRCAN_CONFIG_ATTR(enable0,
		  "Configuration of physical interface 0. Determines\n"	\
		  "the \"Enable 0\" bit of the configuration register.\n" \
		  "Format: 0 | 1\nDefault: 0\n");

GRCAN_CONFIG_ATTR(enable1,
		  "Configuration of physical interface 1. Determines\n"	\
		  "the \"Enable 1\" bit of the configuration register.\n" \
		  "Format: 0 | 1\nDefault: 0\n");

GRCAN_CONFIG_ATTR(select,
		  "Select which physical interface to use.\n"	\
		  "Format: 0 | 1\nDefault: 0\n");

/* The tx and rx buffer size configuration options are only available via module
 * parameters.
 */
GRCAN_MODULE_PARAM(txsize, uint, GRCAN_INVALID_BUFFER_SIZE,
		   "Sets the size of the tx buffer.\n"			\
		   "Format: <unsigned int> where (txsize & ~0x1fffc0) == 0\n" \
		   "Default: 1024\n");
GRCAN_MODULE_PARAM(rxsize, uint, GRCAN_INVALID_BUFFER_SIZE,
		   "Sets the size of the rx buffer.\n"			\
		   "Format: <unsigned int> where (size & ~0x1fffc0) == 0\n" \
		   "Default: 1024\n");

/* Function that makes sure that configuration done using
 * module parameters are set to valid values
 */
static void grcan_sanitize_module_config(struct platform_device *ofdev)
{
	grcan_sanitize_enable0(ofdev);
	grcan_sanitize_enable1(ofdev);
	grcan_sanitize_select(ofdev);
	grcan_sanitize_txsize(ofdev);
	grcan_sanitize_rxsize(ofdev);
}

static const struct attribute *const sysfs_grcan_attrs[] = {
	/* Config attrs */
	&dev_attr_enable0.attr,
	&dev_attr_enable1.attr,
	&dev_attr_select.attr,
	NULL,
};

static const struct attribute_group sysfs_grcan_group = {
	.name	= "grcan",
	.attrs	= (struct attribute **)sysfs_grcan_attrs,
};

/* ========== Setting up the driver ========== */

static const struct net_device_ops grcan_netdev_ops = {
	.ndo_open	= grcan_open,
	.ndo_stop	= grcan_close,
	.ndo_start_xmit	= grcan_start_xmit,
	.ndo_change_mtu = can_change_mtu,
};

static int grcan_setup_netdev(struct platform_device *ofdev,
			      void __iomem *base,
			      int irq, u32 ambafreq, bool txbug)
{
	struct net_device *dev;
	struct grcan_priv *priv;
	struct grcan_registers __iomem *regs;
	int err;

	dev = alloc_candev(sizeof(struct grcan_priv), 0);
	if (!dev)
		return -ENOMEM;

	dev->irq = irq;
	dev->flags |= IFF_ECHO;
	dev->netdev_ops = &grcan_netdev_ops;
	dev->sysfs_groups[0] = &sysfs_grcan_group;

	priv = netdev_priv(dev);
	memcpy(&priv->config, &grcan_module_config,
	       sizeof(struct grcan_device_config));
	priv->dev = dev;
	priv->regs = base;
	priv->can.bittiming_const = &grcan_bittiming_const;
	priv->can.do_set_bittiming = grcan_set_bittiming;
	priv->can.do_set_mode = grcan_set_mode;
	priv->can.do_get_berr_counter = grcan_get_berr_counter;
	priv->can.clock.freq = ambafreq;
	priv->can.ctrlmode_supported =
		CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_ONE_SHOT;
	priv->need_txbug_workaround = txbug;

	/* Discover if triple sampling is supported by hardware */
	regs = priv->regs;
	grcan_set_bits(&regs->ctrl, GRCAN_CTRL_RESET);
	grcan_set_bits(&regs->conf, GRCAN_CONF_SAM);
	if (grcan_read_bits(&regs->conf, GRCAN_CONF_SAM)) {
		priv->can.ctrlmode_supported |= CAN_CTRLMODE_3_SAMPLES;
		dev_dbg(&ofdev->dev, "Hardware supports triple-sampling\n");
	}

	spin_lock_init(&priv->lock);

	if (priv->need_txbug_workaround) {
		init_timer(&priv->rr_timer);
		priv->rr_timer.function = grcan_running_reset;
		priv->rr_timer.data = (unsigned long)dev;

		init_timer(&priv->hang_timer);
		priv->hang_timer.function = grcan_initiate_running_reset;
		priv->hang_timer.data = (unsigned long)dev;
	}

	netif_napi_add(dev, &priv->napi, grcan_poll, GRCAN_NAPI_WEIGHT);

	SET_NETDEV_DEV(dev, &ofdev->dev);
	dev_info(&ofdev->dev, "regs=0x%p, irq=%d, clock=%d\n",
		 priv->regs, dev->irq, priv->can.clock.freq);

	err = register_candev(dev);
	if (err)
		goto exit_free_candev;

	platform_set_drvdata(ofdev, dev);

	/* Reset device to allow bit-timing to be set. No need to call
	 * grcan_reset at this stage. That is done in grcan_open.
	 */
	grcan_write_reg(&regs->ctrl, GRCAN_CTRL_RESET);

	return 0;
exit_free_candev:
	free_candev(dev);
	return err;
}

static int grcan_probe(struct platform_device *ofdev)
{
	struct device_node *np = ofdev->dev.of_node;
	struct resource *res;
	u32 sysid, ambafreq;
	int irq, err;
	void __iomem *base;
	bool txbug = true;

	/* Compare GRLIB version number with the first that does not
	 * have the tx bug (see start_xmit)
	 */
	err = of_property_read_u32(np, "systemid", &sysid);
	if (!err && ((sysid & GRLIB_VERSION_MASK)
		     >= GRCAN_TXBUG_SAFE_GRLIB_VERSION))
		txbug = false;

	err = of_property_read_u32(np, "freq", &ambafreq);
	if (err) {
		dev_err(&ofdev->dev, "unable to fetch \"freq\" property\n");
		goto exit_error;
	}

	res = platform_get_resource(ofdev, IORESOURCE_MEM, 0);
	base = devm_ioremap_resource(&ofdev->dev, res);
	if (IS_ERR(base)) {
		err = PTR_ERR(base);
		goto exit_error;
	}

	irq = irq_of_parse_and_map(np, GRCAN_IRQIX_IRQ);
	if (!irq) {
		dev_err(&ofdev->dev, "no irq found\n");
		err = -ENODEV;
		goto exit_error;
	}

	grcan_sanitize_module_config(ofdev);

	err = grcan_setup_netdev(ofdev, base, irq, ambafreq, txbug);
	if (err)
		goto exit_dispose_irq;

	return 0;

exit_dispose_irq:
	irq_dispose_mapping(irq);
exit_error:
	dev_err(&ofdev->dev,
		"%s socket CAN driver initialization failed with error %d\n",
		DRV_NAME, err);
	return err;
}

static int grcan_remove(struct platform_device *ofdev)
{
	struct net_device *dev = platform_get_drvdata(ofdev);
	struct grcan_priv *priv = netdev_priv(dev);

	unregister_candev(dev); /* Will in turn call grcan_close */

	irq_dispose_mapping(dev->irq);
	netif_napi_del(&priv->napi);
	free_candev(dev);

	return 0;
}

static const struct of_device_id grcan_match[] = {
	{.name = "GAISLER_GRCAN"},
	{.name = "01_03d"},
	{.name = "GAISLER_GRHCAN"},
	{.name = "01_034"},
	{},
};

MODULE_DEVICE_TABLE(of, grcan_match);

static struct platform_driver grcan_driver = {
	.driver = {
		.name = DRV_NAME,
		.of_match_table = grcan_match,
	},
	.probe = grcan_probe,
	.remove = grcan_remove,
};

module_platform_driver(grcan_driver);

MODULE_AUTHOR("Aeroflex Gaisler AB.");
MODULE_DESCRIPTION("Socket CAN driver for Aeroflex Gaisler GRCAN");
MODULE_LICENSE("GPL");