// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * 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.
 *
 * 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(struct timer_list *t)
{
        struct grcan_priv *priv = from_timer(priv, t, rr_timer);
        struct net_device *dev = 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(struct timer_list *t)
{
        struct grcan_priv *priv = from_timer(priv, t, hang_timer);
        struct net_device *dev = 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 = kcalloc(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 = kcalloc(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, 0444);                                \
        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, 0644,                                  \
                           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) {
                timer_setup(&priv->rr_timer, grcan_running_reset, 0);
                timer_setup(&priv->hang_timer, grcan_initiate_running_reset, 0);
        }

        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");