// SPDX-License-Identifier: GPL-2.0-only
/*
 * CAN driver for "8 devices" USB2CAN converter
 *
 * Copyright (C) 2012 Bernd Krumboeck (krumboeck@universalnet.at)
 *
 * This driver is inspired by the 3.2.0 version of drivers/net/can/usb/ems_usb.c
 * and drivers/net/can/usb/esd_usb2.c
 *
 * Many thanks to Gerhard Bertelsmann (info@gerhard-bertelsmann.de)
 * for testing and fixing this driver. Also many thanks to "8 devices",
 * who were very cooperative and answered my questions.
 */

#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/usb.h>

#include <linux/can.h>
#include <linux/can/dev.h>
#include <linux/can/error.h>
#include <linux/can/led.h>

/* driver constants */
#define MAX_RX_URBS                     20
#define MAX_TX_URBS                     20
#define RX_BUFFER_SIZE                  64

/* vendor and product id */
#define USB_8DEV_VENDOR_ID              0x0483
#define USB_8DEV_PRODUCT_ID             0x1234

/* endpoints */
enum usb_8dev_endpoint {
        USB_8DEV_ENDP_DATA_RX = 1,
        USB_8DEV_ENDP_DATA_TX,
        USB_8DEV_ENDP_CMD_RX,
        USB_8DEV_ENDP_CMD_TX
};

/* device CAN clock */
#define USB_8DEV_ABP_CLOCK              32000000

/* setup flags */
#define USB_8DEV_SILENT                 0x01
#define USB_8DEV_LOOPBACK               0x02
#define USB_8DEV_DISABLE_AUTO_RESTRANS  0x04
#define USB_8DEV_STATUS_FRAME           0x08

/* commands */
enum usb_8dev_cmd {
        USB_8DEV_RESET = 1,
        USB_8DEV_OPEN,
        USB_8DEV_CLOSE,
        USB_8DEV_SET_SPEED,
        USB_8DEV_SET_MASK_FILTER,
        USB_8DEV_GET_STATUS,
        USB_8DEV_GET_STATISTICS,
        USB_8DEV_GET_SERIAL,
        USB_8DEV_GET_SOFTW_VER,
        USB_8DEV_GET_HARDW_VER,
        USB_8DEV_RESET_TIMESTAMP,
        USB_8DEV_GET_SOFTW_HARDW_VER
};

/* command options */
#define USB_8DEV_BAUD_MANUAL            0x09
#define USB_8DEV_CMD_START              0x11
#define USB_8DEV_CMD_END                0x22

#define USB_8DEV_CMD_SUCCESS            0
#define USB_8DEV_CMD_ERROR              255

#define USB_8DEV_CMD_TIMEOUT            1000

/* frames */
#define USB_8DEV_DATA_START             0x55
#define USB_8DEV_DATA_END               0xAA

#define USB_8DEV_TYPE_CAN_FRAME         0
#define USB_8DEV_TYPE_ERROR_FRAME       3

#define USB_8DEV_EXTID                  0x01
#define USB_8DEV_RTR                    0x02
#define USB_8DEV_ERR_FLAG               0x04

/* status */
#define USB_8DEV_STATUSMSG_OK           0x00  /* Normal condition. */
#define USB_8DEV_STATUSMSG_OVERRUN      0x01  /* Overrun occured when sending */
#define USB_8DEV_STATUSMSG_BUSLIGHT     0x02  /* Error counter has reached 96 */
#define USB_8DEV_STATUSMSG_BUSHEAVY     0x03  /* Error count. has reached 128 */
#define USB_8DEV_STATUSMSG_BUSOFF       0x04  /* Device is in BUSOFF */
#define USB_8DEV_STATUSMSG_STUFF        0x20  /* Stuff Error */
#define USB_8DEV_STATUSMSG_FORM         0x21  /* Form Error */
#define USB_8DEV_STATUSMSG_ACK          0x23  /* Ack Error */
#define USB_8DEV_STATUSMSG_BIT0         0x24  /* Bit1 Error */
#define USB_8DEV_STATUSMSG_BIT1         0x25  /* Bit0 Error */
#define USB_8DEV_STATUSMSG_CRC          0x27  /* CRC Error */

#define USB_8DEV_RP_MASK                0x7F  /* Mask for Receive Error Bit */


/* table of devices that work with this driver */
static const struct usb_device_id usb_8dev_table[] = {
        { USB_DEVICE(USB_8DEV_VENDOR_ID, USB_8DEV_PRODUCT_ID) },
        { }                                     /* Terminating entry */
};

MODULE_DEVICE_TABLE(usb, usb_8dev_table);

struct usb_8dev_tx_urb_context {
        struct usb_8dev_priv *priv;

        u32 echo_index;
        u8 dlc;
};

/* Structure to hold all of our device specific stuff */
struct usb_8dev_priv {
        struct can_priv can; /* must be the first member */

        struct sk_buff *echo_skb[MAX_TX_URBS];

        struct usb_device *udev;
        struct net_device *netdev;

        atomic_t active_tx_urbs;
        struct usb_anchor tx_submitted;
        struct usb_8dev_tx_urb_context tx_contexts[MAX_TX_URBS];

        struct usb_anchor rx_submitted;

        struct can_berr_counter bec;

        u8 *cmd_msg_buffer;

        struct mutex usb_8dev_cmd_lock;

};

/* tx frame */
struct __packed usb_8dev_tx_msg {
        u8 begin;
        u8 flags;       /* RTR and EXT_ID flag */
        __be32 id;      /* upper 3 bits not used */
        u8 dlc;         /* data length code 0-8 bytes */
        u8 data[8];     /* 64-bit data */
        u8 end;
};

/* rx frame */
struct __packed usb_8dev_rx_msg {
        u8 begin;
        u8 type;                /* frame type */
        u8 flags;               /* RTR and EXT_ID flag */
        __be32 id;              /* upper 3 bits not used */
        u8 dlc;                 /* data length code 0-8 bytes */
        u8 data[8];             /* 64-bit data */
        __be32 timestamp;       /* 32-bit timestamp */
        u8 end;
};

/* command frame */
struct __packed usb_8dev_cmd_msg {
        u8 begin;
        u8 channel;     /* unkown - always 0 */
        u8 command;     /* command to execute */
        u8 opt1;        /* optional parameter / return value */
        u8 opt2;        /* optional parameter 2 */
        u8 data[10];    /* optional parameter and data */
        u8 end;
};

static int usb_8dev_send_cmd_msg(struct usb_8dev_priv *priv, u8 *msg, int size)
{
        int actual_length;

        return usb_bulk_msg(priv->udev,
                            usb_sndbulkpipe(priv->udev, USB_8DEV_ENDP_CMD_TX),
                            msg, size, &actual_length, USB_8DEV_CMD_TIMEOUT);
}

static int usb_8dev_wait_cmd_msg(struct usb_8dev_priv *priv, u8 *msg, int size,
                                int *actual_length)
{
        return usb_bulk_msg(priv->udev,
                            usb_rcvbulkpipe(priv->udev, USB_8DEV_ENDP_CMD_RX),
                            msg, size, actual_length, USB_8DEV_CMD_TIMEOUT);
}

/* Send command to device and receive result.
 * Command was successful when opt1 = 0.
 */
static int usb_8dev_send_cmd(struct usb_8dev_priv *priv,
                             struct usb_8dev_cmd_msg *out,
                             struct usb_8dev_cmd_msg *in)
{
        int err;
        int num_bytes_read;
        struct net_device *netdev;

        netdev = priv->netdev;

        out->begin = USB_8DEV_CMD_START;
        out->end = USB_8DEV_CMD_END;

        mutex_lock(&priv->usb_8dev_cmd_lock);

        memcpy(priv->cmd_msg_buffer, out,
                sizeof(struct usb_8dev_cmd_msg));

        err = usb_8dev_send_cmd_msg(priv, priv->cmd_msg_buffer,
                                    sizeof(struct usb_8dev_cmd_msg));
        if (err < 0) {
                netdev_err(netdev, "sending command message failed\n");
                goto failed;
        }

        err = usb_8dev_wait_cmd_msg(priv, priv->cmd_msg_buffer,
                                    sizeof(struct usb_8dev_cmd_msg),
                                    &num_bytes_read);
        if (err < 0) {
                netdev_err(netdev, "no command message answer\n");
                goto failed;
        }

        memcpy(in, priv->cmd_msg_buffer, sizeof(struct usb_8dev_cmd_msg));

        if (in->begin != USB_8DEV_CMD_START || in->end != USB_8DEV_CMD_END ||
                        num_bytes_read != 16 || in->opt1 != 0)
                err = -EPROTO;

failed:
        mutex_unlock(&priv->usb_8dev_cmd_lock);
        return err;
}

/* Send open command to device */
static int usb_8dev_cmd_open(struct usb_8dev_priv *priv)
{
        struct can_bittiming *bt = &priv->can.bittiming;
        struct usb_8dev_cmd_msg outmsg;
        struct usb_8dev_cmd_msg inmsg;
        u32 ctrlmode = priv->can.ctrlmode;
        u32 flags = USB_8DEV_STATUS_FRAME;
        __be32 beflags;
        __be16 bebrp;

        memset(&outmsg, 0, sizeof(outmsg));
        outmsg.command = USB_8DEV_OPEN;
        outmsg.opt1 = USB_8DEV_BAUD_MANUAL;
        outmsg.data[0] = bt->prop_seg + bt->phase_seg1;
        outmsg.data[1] = bt->phase_seg2;
        outmsg.data[2] = bt->sjw;

        /* BRP */
        bebrp = cpu_to_be16((u16)bt->brp);
        memcpy(&outmsg.data[3], &bebrp, sizeof(bebrp));

        /* flags */
        if (ctrlmode & CAN_CTRLMODE_LOOPBACK)
                flags |= USB_8DEV_LOOPBACK;
        if (ctrlmode & CAN_CTRLMODE_LISTENONLY)
                flags |= USB_8DEV_SILENT;
        if (ctrlmode & CAN_CTRLMODE_ONE_SHOT)
                flags |= USB_8DEV_DISABLE_AUTO_RESTRANS;

        beflags = cpu_to_be32(flags);
        memcpy(&outmsg.data[5], &beflags, sizeof(beflags));

        return usb_8dev_send_cmd(priv, &outmsg, &inmsg);
}

/* Send close command to device */
static int usb_8dev_cmd_close(struct usb_8dev_priv *priv)
{
        struct usb_8dev_cmd_msg inmsg;
        struct usb_8dev_cmd_msg outmsg = {
                .channel = 0,
                .command = USB_8DEV_CLOSE,
                .opt1 = 0,
                .opt2 = 0
        };

        return usb_8dev_send_cmd(priv, &outmsg, &inmsg);
}

/* Get firmware and hardware version */
static int usb_8dev_cmd_version(struct usb_8dev_priv *priv, u32 *res)
{
        struct usb_8dev_cmd_msg inmsg;
        struct usb_8dev_cmd_msg outmsg = {
                .channel = 0,
                .command = USB_8DEV_GET_SOFTW_HARDW_VER,
                .opt1 = 0,
                .opt2 = 0
        };

        int err = usb_8dev_send_cmd(priv, &outmsg, &inmsg);
        if (err)
                return err;

        *res = be32_to_cpup((__be32 *)inmsg.data);

        return err;
}

/* Set network device mode
 *
 * Maybe we should leave this function empty, because the device
 * set mode variable with open command.
 */
static int usb_8dev_set_mode(struct net_device *netdev, enum can_mode mode)
{
        struct usb_8dev_priv *priv = netdev_priv(netdev);
        int err = 0;

        switch (mode) {
        case CAN_MODE_START:
                err = usb_8dev_cmd_open(priv);
                if (err)
                        netdev_warn(netdev, "couldn't start device");
                break;

        default:
                return -EOPNOTSUPP;
        }

        return err;
}

/* Read error/status frames */
static void usb_8dev_rx_err_msg(struct usb_8dev_priv *priv,
                                struct usb_8dev_rx_msg *msg)
{
        struct can_frame *cf;
        struct sk_buff *skb;
        struct net_device_stats *stats = &priv->netdev->stats;

        /* Error message:
         * byte 0: Status
         * byte 1: bit   7: Receive Passive
         * byte 1: bit 0-6: Receive Error Counter
         * byte 2: Transmit Error Counter
         * byte 3: Always 0 (maybe reserved for future use)
         */

        u8 state = msg->data[0];
        u8 rxerr = msg->data[1] & USB_8DEV_RP_MASK;
        u8 txerr = msg->data[2];
        int rx_errors = 0;
        int tx_errors = 0;

        skb = alloc_can_err_skb(priv->netdev, &cf);
        if (!skb)
                return;

        switch (state) {
        case USB_8DEV_STATUSMSG_OK:
                priv->can.state = CAN_STATE_ERROR_ACTIVE;
                cf->can_id |= CAN_ERR_PROT;
                cf->data[2] = CAN_ERR_PROT_ACTIVE;
                break;
        case USB_8DEV_STATUSMSG_BUSOFF:
                priv->can.state = CAN_STATE_BUS_OFF;
                cf->can_id |= CAN_ERR_BUSOFF;
                priv->can.can_stats.bus_off++;
                can_bus_off(priv->netdev);
                break;
        case USB_8DEV_STATUSMSG_OVERRUN:
        case USB_8DEV_STATUSMSG_BUSLIGHT:
        case USB_8DEV_STATUSMSG_BUSHEAVY:
                cf->can_id |= CAN_ERR_CRTL;
                break;
        default:
                priv->can.state = CAN_STATE_ERROR_WARNING;
                cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;
                priv->can.can_stats.bus_error++;
                break;
        }

        switch (state) {
        case USB_8DEV_STATUSMSG_OK:
        case USB_8DEV_STATUSMSG_BUSOFF:
                break;
        case USB_8DEV_STATUSMSG_ACK:
                cf->can_id |= CAN_ERR_ACK;
                tx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_CRC:
                cf->data[3] = CAN_ERR_PROT_LOC_CRC_SEQ;
                rx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_BIT0:
                cf->data[2] |= CAN_ERR_PROT_BIT0;
                tx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_BIT1:
                cf->data[2] |= CAN_ERR_PROT_BIT1;
                tx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_FORM:
                cf->data[2] |= CAN_ERR_PROT_FORM;
                rx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_STUFF:
                cf->data[2] |= CAN_ERR_PROT_STUFF;
                rx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_OVERRUN:
                cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
                stats->rx_over_errors++;
                rx_errors = 1;
                break;
        case USB_8DEV_STATUSMSG_BUSLIGHT:
                priv->can.state = CAN_STATE_ERROR_WARNING;
                cf->data[1] = (txerr > rxerr) ?
                        CAN_ERR_CRTL_TX_WARNING :
                        CAN_ERR_CRTL_RX_WARNING;
                priv->can.can_stats.error_warning++;
                break;
        case USB_8DEV_STATUSMSG_BUSHEAVY:
                priv->can.state = CAN_STATE_ERROR_PASSIVE;
                cf->data[1] = (txerr > rxerr) ?
                        CAN_ERR_CRTL_TX_PASSIVE :
                        CAN_ERR_CRTL_RX_PASSIVE;
                priv->can.can_stats.error_passive++;
                break;
        default:
                netdev_warn(priv->netdev,
                            "Unknown status/error message (%d)\n", state);
                break;
        }

        if (tx_errors) {
                cf->data[2] |= CAN_ERR_PROT_TX;
                stats->tx_errors++;
        }

        if (rx_errors)
                stats->rx_errors++;

        cf->data[6] = txerr;
        cf->data[7] = rxerr;

        priv->bec.txerr = txerr;
        priv->bec.rxerr = rxerr;

        stats->rx_packets++;
        stats->rx_bytes += cf->can_dlc;
        netif_rx(skb);
}

/* Read data and status frames */
static void usb_8dev_rx_can_msg(struct usb_8dev_priv *priv,
                                struct usb_8dev_rx_msg *msg)
{
        struct can_frame *cf;
        struct sk_buff *skb;
        struct net_device_stats *stats = &priv->netdev->stats;

        if (msg->type == USB_8DEV_TYPE_ERROR_FRAME &&
                   msg->flags == USB_8DEV_ERR_FLAG) {
                usb_8dev_rx_err_msg(priv, msg);
        } else if (msg->type == USB_8DEV_TYPE_CAN_FRAME) {
                skb = alloc_can_skb(priv->netdev, &cf);
                if (!skb)
                        return;

                cf->can_id = be32_to_cpu(msg->id);
                cf->can_dlc = get_can_dlc(msg->dlc & 0xF);

                if (msg->flags & USB_8DEV_EXTID)
                        cf->can_id |= CAN_EFF_FLAG;

                if (msg->flags & USB_8DEV_RTR)
                        cf->can_id |= CAN_RTR_FLAG;
                else
                        memcpy(cf->data, msg->data, cf->can_dlc);

                stats->rx_packets++;
                stats->rx_bytes += cf->can_dlc;
                netif_rx(skb);

                can_led_event(priv->netdev, CAN_LED_EVENT_RX);
        } else {
                netdev_warn(priv->netdev, "frame type %d unknown",
                         msg->type);
        }

}

/* Callback for reading data from device
 *
 * Check urb status, call read function and resubmit urb read operation.
 */
static void usb_8dev_read_bulk_callback(struct urb *urb)
{
        struct usb_8dev_priv *priv = urb->context;
        struct net_device *netdev;
        int retval;
        int pos = 0;

        netdev = priv->netdev;

        if (!netif_device_present(netdev))
                return;

        switch (urb->status) {
        case 0: /* success */
                break;

        case -ENOENT:
        case -EPIPE:
        case -EPROTO:
        case -ESHUTDOWN:
                return;

        default:
                netdev_info(netdev, "Rx URB aborted (%d)\n",
                         urb->status);
                goto resubmit_urb;
        }

        while (pos < urb->actual_length) {
                struct usb_8dev_rx_msg *msg;

                if (pos + sizeof(struct usb_8dev_rx_msg) > urb->actual_length) {
                        netdev_err(priv->netdev, "format error\n");
                        break;
                }

                msg = (struct usb_8dev_rx_msg *)(urb->transfer_buffer + pos);
                usb_8dev_rx_can_msg(priv, msg);

                pos += sizeof(struct usb_8dev_rx_msg);
        }

resubmit_urb:
        usb_fill_bulk_urb(urb, priv->udev,
                          usb_rcvbulkpipe(priv->udev, USB_8DEV_ENDP_DATA_RX),
                          urb->transfer_buffer, RX_BUFFER_SIZE,
                          usb_8dev_read_bulk_callback, priv);

        retval = usb_submit_urb(urb, GFP_ATOMIC);

        if (retval == -ENODEV)
                netif_device_detach(netdev);
        else if (retval)
                netdev_err(netdev,
                        "failed resubmitting read bulk urb: %d\n", retval);
}

/* Callback handler for write operations
 *
 * Free allocated buffers, check transmit status and
 * calculate statistic.
 */
static void usb_8dev_write_bulk_callback(struct urb *urb)
{
        struct usb_8dev_tx_urb_context *context = urb->context;
        struct usb_8dev_priv *priv;
        struct net_device *netdev;

        BUG_ON(!context);

        priv = context->priv;
        netdev = priv->netdev;

        /* free up our allocated buffer */
        usb_free_coherent(urb->dev, urb->transfer_buffer_length,
                          urb->transfer_buffer, urb->transfer_dma);

        atomic_dec(&priv->active_tx_urbs);

        if (!netif_device_present(netdev))
                return;

        if (urb->status)
                netdev_info(netdev, "Tx URB aborted (%d)\n",
                         urb->status);

        netdev->stats.tx_packets++;
        netdev->stats.tx_bytes += context->dlc;

        can_get_echo_skb(netdev, context->echo_index);

        can_led_event(netdev, CAN_LED_EVENT_TX);

        /* Release context */
        context->echo_index = MAX_TX_URBS;

        netif_wake_queue(netdev);
}

/* Send data to device */
static netdev_tx_t usb_8dev_start_xmit(struct sk_buff *skb,
                                      struct net_device *netdev)
{
        struct usb_8dev_priv *priv = netdev_priv(netdev);
        struct net_device_stats *stats = &netdev->stats;
        struct can_frame *cf = (struct can_frame *) skb->data;
        struct usb_8dev_tx_msg *msg;
        struct urb *urb;
        struct usb_8dev_tx_urb_context *context = NULL;
        u8 *buf;
        int i, err;
        size_t size = sizeof(struct usb_8dev_tx_msg);

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

        /* create a URB, and a buffer for it, and copy the data to the URB */
        urb = usb_alloc_urb(0, GFP_ATOMIC);
        if (!urb)
                goto nomem;

        buf = usb_alloc_coherent(priv->udev, size, GFP_ATOMIC,
                                 &urb->transfer_dma);
        if (!buf) {
                netdev_err(netdev, "No memory left for USB buffer\n");
                goto nomembuf;
        }

        memset(buf, 0, size);

        msg = (struct usb_8dev_tx_msg *)buf;
        msg->begin = USB_8DEV_DATA_START;
        msg->flags = 0x00;

        if (cf->can_id & CAN_RTR_FLAG)
                msg->flags |= USB_8DEV_RTR;

        if (cf->can_id & CAN_EFF_FLAG)
                msg->flags |= USB_8DEV_EXTID;

        msg->id = cpu_to_be32(cf->can_id & CAN_ERR_MASK);
        msg->dlc = cf->can_dlc;
        memcpy(msg->data, cf->data, cf->can_dlc);
        msg->end = USB_8DEV_DATA_END;

        for (i = 0; i < MAX_TX_URBS; i++) {
                if (priv->tx_contexts[i].echo_index == MAX_TX_URBS) {
                        context = &priv->tx_contexts[i];
                        break;
                }
        }

        /* May never happen! When this happens we'd more URBs in flight as
         * allowed (MAX_TX_URBS).
         */
        if (!context)
                goto nofreecontext;

        context->priv = priv;
        context->echo_index = i;
        context->dlc = cf->can_dlc;

        usb_fill_bulk_urb(urb, priv->udev,
                          usb_sndbulkpipe(priv->udev, USB_8DEV_ENDP_DATA_TX),
                          buf, size, usb_8dev_write_bulk_callback, context);
        urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
        usb_anchor_urb(urb, &priv->tx_submitted);

        can_put_echo_skb(skb, netdev, context->echo_index);

        atomic_inc(&priv->active_tx_urbs);

        err = usb_submit_urb(urb, GFP_ATOMIC);
        if (unlikely(err))
                goto failed;
        else if (atomic_read(&priv->active_tx_urbs) >= MAX_TX_URBS)
                /* Slow down tx path */
                netif_stop_queue(netdev);

        /* Release our reference to this URB, the USB core will eventually free
         * it entirely.
         */
        usb_free_urb(urb);

        return NETDEV_TX_OK;

nofreecontext:
        usb_free_coherent(priv->udev, size, buf, urb->transfer_dma);
        usb_free_urb(urb);

        netdev_warn(netdev, "couldn't find free context");

        return NETDEV_TX_BUSY;

failed:
        can_free_echo_skb(netdev, context->echo_index);

        usb_unanchor_urb(urb);
        usb_free_coherent(priv->udev, size, buf, urb->transfer_dma);

        atomic_dec(&priv->active_tx_urbs);

        if (err == -ENODEV)
                netif_device_detach(netdev);
        else
                netdev_warn(netdev, "failed tx_urb %d\n", err);

nomembuf:
        usb_free_urb(urb);

nomem:
        dev_kfree_skb(skb);
        stats->tx_dropped++;

        return NETDEV_TX_OK;
}

static int usb_8dev_get_berr_counter(const struct net_device *netdev,
                                     struct can_berr_counter *bec)
{
        struct usb_8dev_priv *priv = netdev_priv(netdev);

        bec->txerr = priv->bec.txerr;
        bec->rxerr = priv->bec.rxerr;

        return 0;
}

/* Start USB device */
static int usb_8dev_start(struct usb_8dev_priv *priv)
{
        struct net_device *netdev = priv->netdev;
        int err, i;

        for (i = 0; i < MAX_RX_URBS; i++) {
                struct urb *urb = NULL;
                u8 *buf;

                /* create a URB, and a buffer for it */
                urb = usb_alloc_urb(0, GFP_KERNEL);
                if (!urb) {
                        err = -ENOMEM;
                        break;
                }

                buf = usb_alloc_coherent(priv->udev, RX_BUFFER_SIZE, GFP_KERNEL,
                                         &urb->transfer_dma);
                if (!buf) {
                        netdev_err(netdev, "No memory left for USB buffer\n");
                        usb_free_urb(urb);
                        err = -ENOMEM;
                        break;
                }

                usb_fill_bulk_urb(urb, priv->udev,
                                  usb_rcvbulkpipe(priv->udev,
                                                  USB_8DEV_ENDP_DATA_RX),
                                  buf, RX_BUFFER_SIZE,
                                  usb_8dev_read_bulk_callback, priv);
                urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
                usb_anchor_urb(urb, &priv->rx_submitted);

                err = usb_submit_urb(urb, GFP_KERNEL);
                if (err) {
                        usb_unanchor_urb(urb);
                        usb_free_coherent(priv->udev, RX_BUFFER_SIZE, buf,
                                          urb->transfer_dma);
                        usb_free_urb(urb);
                        break;
                }

                /* Drop reference, USB core will take care of freeing it */
                usb_free_urb(urb);
        }

        /* Did we submit any URBs */
        if (i == 0) {
                netdev_warn(netdev, "couldn't setup read URBs\n");
                return err;
        }

        /* Warn if we've couldn't transmit all the URBs */
        if (i < MAX_RX_URBS)
                netdev_warn(netdev, "rx performance may be slow\n");

        err = usb_8dev_cmd_open(priv);
        if (err)
                goto failed;

        priv->can.state = CAN_STATE_ERROR_ACTIVE;

        return 0;

failed:
        if (err == -ENODEV)
                netif_device_detach(priv->netdev);

        netdev_warn(netdev, "couldn't submit control: %d\n", err);

        return err;
}

/* Open USB device */
static int usb_8dev_open(struct net_device *netdev)
{
        struct usb_8dev_priv *priv = netdev_priv(netdev);
        int err;

        /* common open */
        err = open_candev(netdev);
        if (err)
                return err;

        can_led_event(netdev, CAN_LED_EVENT_OPEN);

        /* finally start device */
        err = usb_8dev_start(priv);
        if (err) {
                if (err == -ENODEV)
                        netif_device_detach(priv->netdev);

                netdev_warn(netdev, "couldn't start device: %d\n",
                         err);

                close_candev(netdev);

                return err;
        }

        netif_start_queue(netdev);

        return 0;
}

static void unlink_all_urbs(struct usb_8dev_priv *priv)
{
        int i;

        usb_kill_anchored_urbs(&priv->rx_submitted);

        usb_kill_anchored_urbs(&priv->tx_submitted);
        atomic_set(&priv->active_tx_urbs, 0);

        for (i = 0; i < MAX_TX_URBS; i++)
                priv->tx_contexts[i].echo_index = MAX_TX_URBS;
}

/* Close USB device */
static int usb_8dev_close(struct net_device *netdev)
{
        struct usb_8dev_priv *priv = netdev_priv(netdev);
        int err = 0;

        /* Send CLOSE command to CAN controller */
        err = usb_8dev_cmd_close(priv);
        if (err)
                netdev_warn(netdev, "couldn't stop device");

        priv->can.state = CAN_STATE_STOPPED;

        netif_stop_queue(netdev);

        /* Stop polling */
        unlink_all_urbs(priv);

        close_candev(netdev);

        can_led_event(netdev, CAN_LED_EVENT_STOP);

        return err;
}

static const struct net_device_ops usb_8dev_netdev_ops = {
        .ndo_open = usb_8dev_open,
        .ndo_stop = usb_8dev_close,
        .ndo_start_xmit = usb_8dev_start_xmit,
        .ndo_change_mtu = can_change_mtu,
};

static const struct can_bittiming_const usb_8dev_bittiming_const = {
        .name = "usb_8dev",
        .tseg1_min = 1,
        .tseg1_max = 16,
        .tseg2_min = 1,
        .tseg2_max = 8,
        .sjw_max = 4,
        .brp_min = 1,
        .brp_max = 1024,
        .brp_inc = 1,
};

/* Probe USB device
 *
 * Check device and firmware.
 * Set supported modes and bittiming constants.
 * Allocate some memory.
 */
static int usb_8dev_probe(struct usb_interface *intf,
                         const struct usb_device_id *id)
{
        struct net_device *netdev;
        struct usb_8dev_priv *priv;
        int i, err = -ENOMEM;
        u32 version;
        char buf[18];
        struct usb_device *usbdev = interface_to_usbdev(intf);

        /* product id looks strange, better we also check iProduct string */
        if (usb_string(usbdev, usbdev->descriptor.iProduct, buf,
                       sizeof(buf)) > 0 && strcmp(buf, "USB2CAN converter")) {
                dev_info(&usbdev->dev, "ignoring: not an USB2CAN converter\n");
                return -ENODEV;
        }

        netdev = alloc_candev(sizeof(struct usb_8dev_priv), MAX_TX_URBS);
        if (!netdev) {
                dev_err(&intf->dev, "Couldn't alloc candev\n");
                return -ENOMEM;
        }

        priv = netdev_priv(netdev);

        priv->udev = usbdev;
        priv->netdev = netdev;

        priv->can.state = CAN_STATE_STOPPED;
        priv->can.clock.freq = USB_8DEV_ABP_CLOCK;
        priv->can.bittiming_const = &usb_8dev_bittiming_const;
        priv->can.do_set_mode = usb_8dev_set_mode;
        priv->can.do_get_berr_counter = usb_8dev_get_berr_counter;
        priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
                                      CAN_CTRLMODE_LISTENONLY |
                                      CAN_CTRLMODE_ONE_SHOT;

        netdev->netdev_ops = &usb_8dev_netdev_ops;

        netdev->flags |= IFF_ECHO; /* we support local echo */

        init_usb_anchor(&priv->rx_submitted);

        init_usb_anchor(&priv->tx_submitted);
        atomic_set(&priv->active_tx_urbs, 0);

        for (i = 0; i < MAX_TX_URBS; i++)
                priv->tx_contexts[i].echo_index = MAX_TX_URBS;

        priv->cmd_msg_buffer = devm_kzalloc(&intf->dev, sizeof(struct usb_8dev_cmd_msg),
                                            GFP_KERNEL);
        if (!priv->cmd_msg_buffer)
                goto cleanup_candev;

        usb_set_intfdata(intf, priv);

        SET_NETDEV_DEV(netdev, &intf->dev);

        mutex_init(&priv->usb_8dev_cmd_lock);

        err = register_candev(netdev);
        if (err) {
                netdev_err(netdev,
                        "couldn't register CAN device: %d\n", err);
                goto cleanup_candev;
        }

        err = usb_8dev_cmd_version(priv, &version);
        if (err) {
                netdev_err(netdev, "can't get firmware version\n");
                goto cleanup_unregister_candev;
        } else {
                netdev_info(netdev,
                         "firmware: %d.%d, hardware: %d.%d\n",
                         (version>>24) & 0xff, (version>>16) & 0xff,
                         (version>>8) & 0xff, version & 0xff);
        }

        devm_can_led_init(netdev);

        return 0;

cleanup_unregister_candev:
        unregister_netdev(priv->netdev);

cleanup_candev:
        free_candev(netdev);

        return err;

}

/* Called by the usb core when driver is unloaded or device is removed */
static void usb_8dev_disconnect(struct usb_interface *intf)
{
        struct usb_8dev_priv *priv = usb_get_intfdata(intf);

        usb_set_intfdata(intf, NULL);

        if (priv) {
                netdev_info(priv->netdev, "device disconnected\n");

                unregister_netdev(priv->netdev);
                unlink_all_urbs(priv);
                free_candev(priv->netdev);

        }

}

static struct usb_driver usb_8dev_driver = {
        .name =         "usb_8dev",
        .probe =        usb_8dev_probe,
        .disconnect =   usb_8dev_disconnect,
        .id_table =     usb_8dev_table,
};

module_usb_driver(usb_8dev_driver);

MODULE_AUTHOR("Bernd Krumboeck <krumboeck@universalnet.at>");
MODULE_DESCRIPTION("CAN driver for 8 devices USB2CAN interfaces");
MODULE_LICENSE("GPL v2");