/*
 * CAN driver for EMS Dr. Thomas Wuensche CPC-USB/ARM7
 *
 * Copyright (C) 2004-2009 EMS Dr. Thomas Wuensche
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published
 * by the Free Software Foundation; version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#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>

MODULE_AUTHOR("Sebastian Haas <haas@ems-wuensche.com>");
MODULE_DESCRIPTION("CAN driver for EMS Dr. Thomas Wuensche CAN/USB interfaces");
MODULE_LICENSE("GPL v2");

/* Control-Values for CPC_Control() Command Subject Selection */
#define CONTR_CAN_MESSAGE 0x04
#define CONTR_CAN_STATE   0x0C
#define CONTR_BUS_ERROR   0x1C

/* Control Command Actions */
#define CONTR_CONT_OFF 0
#define CONTR_CONT_ON  1
#define CONTR_ONCE     2

/* Messages from CPC to PC */
#define CPC_MSG_TYPE_CAN_FRAME       1  /* CAN data frame */
#define CPC_MSG_TYPE_RTR_FRAME       8  /* CAN remote frame */
#define CPC_MSG_TYPE_CAN_PARAMS      12 /* Actual CAN parameters */
#define CPC_MSG_TYPE_CAN_STATE       14 /* CAN state message */
#define CPC_MSG_TYPE_EXT_CAN_FRAME   16 /* Extended CAN data frame */
#define CPC_MSG_TYPE_EXT_RTR_FRAME   17 /* Extended remote frame */
#define CPC_MSG_TYPE_CONTROL         19 /* change interface behavior */
#define CPC_MSG_TYPE_CONFIRM         20 /* command processed confirmation */
#define CPC_MSG_TYPE_OVERRUN         21 /* overrun events */
#define CPC_MSG_TYPE_CAN_FRAME_ERROR 23 /* detected bus errors */
#define CPC_MSG_TYPE_ERR_COUNTER     25 /* RX/TX error counter */

/* Messages from the PC to the CPC interface  */
#define CPC_CMD_TYPE_CAN_FRAME     1   /* CAN data frame */
#define CPC_CMD_TYPE_CONTROL       3   /* control of interface behavior */
#define CPC_CMD_TYPE_CAN_PARAMS    6   /* set CAN parameters */
#define CPC_CMD_TYPE_RTR_FRAME     13  /* CAN remote frame */
#define CPC_CMD_TYPE_CAN_STATE     14  /* CAN state message */
#define CPC_CMD_TYPE_EXT_CAN_FRAME 15  /* Extended CAN data frame */
#define CPC_CMD_TYPE_EXT_RTR_FRAME 16  /* Extended CAN remote frame */
#define CPC_CMD_TYPE_CAN_EXIT      200 /* exit the CAN */

#define CPC_CMD_TYPE_INQ_ERR_COUNTER 25 /* request the CAN error counters */
#define CPC_CMD_TYPE_CLEAR_MSG_QUEUE 8  /* clear CPC_MSG queue */
#define CPC_CMD_TYPE_CLEAR_CMD_QUEUE 28 /* clear CPC_CMD queue */

#define CPC_CC_TYPE_SJA1000 2 /* Philips basic CAN controller */

#define CPC_CAN_ECODE_ERRFRAME 0x01 /* Ecode type */

/* Overrun types */
#define CPC_OVR_EVENT_CAN       0x01
#define CPC_OVR_EVENT_CANSTATE  0x02
#define CPC_OVR_EVENT_BUSERROR  0x04

/*
 * If the CAN controller lost a message we indicate it with the highest bit
 * set in the count field.
 */
#define CPC_OVR_HW 0x80

/* Size of the "struct ems_cpc_msg" without the union */
#define CPC_MSG_HEADER_LEN   11
#define CPC_CAN_MSG_MIN_SIZE 5

/* Define these values to match your devices */
#define USB_CPCUSB_VENDOR_ID 0x12D6

#define USB_CPCUSB_ARM7_PRODUCT_ID 0x0444

/* Mode register NXP LPC2119/SJA1000 CAN Controller */
#define SJA1000_MOD_NORMAL 0x00
#define SJA1000_MOD_RM     0x01

/* ECC register NXP LPC2119/SJA1000 CAN Controller */
#define SJA1000_ECC_SEG   0x1F
#define SJA1000_ECC_DIR   0x20
#define SJA1000_ECC_ERR   0x06
#define SJA1000_ECC_BIT   0x00
#define SJA1000_ECC_FORM  0x40
#define SJA1000_ECC_STUFF 0x80
#define SJA1000_ECC_MASK  0xc0

/* Status register content */
#define SJA1000_SR_BS 0x80
#define SJA1000_SR_ES 0x40

#define SJA1000_DEFAULT_OUTPUT_CONTROL 0xDA

/*
 * The device actually uses a 16MHz clock to generate the CAN clock
 * but it expects SJA1000 bit settings based on 8MHz (is internally
 * converted).
 */
#define EMS_USB_ARM7_CLOCK 8000000

/*
 * CAN-Message representation in a CPC_MSG. Message object type is
 * CPC_MSG_TYPE_CAN_FRAME or CPC_MSG_TYPE_RTR_FRAME or
 * CPC_MSG_TYPE_EXT_CAN_FRAME or CPC_MSG_TYPE_EXT_RTR_FRAME.
 */
struct cpc_can_msg {
        __le32 id;
        u8 length;
        u8 msg[8];
};

/* Representation of the CAN parameters for the SJA1000 controller */
struct cpc_sja1000_params {
        u8 mode;
        u8 acc_code0;
        u8 acc_code1;
        u8 acc_code2;
        u8 acc_code3;
        u8 acc_mask0;
        u8 acc_mask1;
        u8 acc_mask2;
        u8 acc_mask3;
        u8 btr0;
        u8 btr1;
        u8 outp_contr;
};

/* CAN params message representation */
struct cpc_can_params {
        u8 cc_type;

        /* Will support M16C CAN controller in the future */
        union {
                struct cpc_sja1000_params sja1000;
        } cc_params;
};

/* Structure for confirmed message handling */
struct cpc_confirm {
        u8 error; /* error code */
};

/* Structure for overrun conditions */
struct cpc_overrun {
        u8 event;
        u8 count;
};

/* SJA1000 CAN errors (compatible to NXP LPC2119) */
struct cpc_sja1000_can_error {
        u8 ecc;
        u8 rxerr;
        u8 txerr;
};

/* structure for CAN error conditions */
struct cpc_can_error {
        u8 ecode;

        struct {
                u8 cc_type;

                /* Other controllers may also provide error code capture regs */
                union {
                        struct cpc_sja1000_can_error sja1000;
                } regs;
        } cc;
};

/*
 * Structure containing RX/TX error counter. This structure is used to request
 * the values of the CAN controllers TX and RX error counter.
 */
struct cpc_can_err_counter {
        u8 rx;
        u8 tx;
};

/* Main message type used between library and application */
struct __packed ems_cpc_msg {
        u8 type;        /* type of message */
        u8 length;      /* length of data within union 'msg' */
        u8 msgid;       /* confirmation handle */
        __le32 ts_sec;  /* timestamp in seconds */
        __le32 ts_nsec; /* timestamp in nano seconds */

        union {
                u8 generic[64];
                struct cpc_can_msg can_msg;
                struct cpc_can_params can_params;
                struct cpc_confirm confirmation;
                struct cpc_overrun overrun;
                struct cpc_can_error error;
                struct cpc_can_err_counter err_counter;
                u8 can_state;
        } msg;
};

/*
 * Table of devices that work with this driver
 * NOTE: This driver supports only CPC-USB/ARM7 (LPC2119) yet.
 */
static struct usb_device_id ems_usb_table[] = {
        {USB_DEVICE(USB_CPCUSB_VENDOR_ID, USB_CPCUSB_ARM7_PRODUCT_ID)},
        {} /* Terminating entry */
};

MODULE_DEVICE_TABLE(usb, ems_usb_table);

#define RX_BUFFER_SIZE      64
#define CPC_HEADER_SIZE     4
#define INTR_IN_BUFFER_SIZE 4

#define MAX_RX_URBS 10
#define MAX_TX_URBS 10

struct ems_usb;

struct ems_tx_urb_context {
        struct ems_usb *dev;

        u32 echo_index;
        u8 dlc;
};

struct ems_usb {
        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 ems_tx_urb_context tx_contexts[MAX_TX_URBS];

        struct usb_anchor rx_submitted;

        struct urb *intr_urb;

        u8 *tx_msg_buffer;

        u8 *intr_in_buffer;
        unsigned int free_slots; /* remember number of available slots */

        struct ems_cpc_msg active_params; /* active controller parameters */
};

static void ems_usb_read_interrupt_callback(struct urb *urb)
{
        struct ems_usb *dev = urb->context;
        struct net_device *netdev = dev->netdev;
        int err;

        if (!netif_device_present(netdev))
                return;

        switch (urb->status) {
        case 0:
                dev->free_slots = dev->intr_in_buffer[1];
                break;

        case -ECONNRESET: /* unlink */
        case -ENOENT:
        case -ESHUTDOWN:
                return;

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

        err = usb_submit_urb(urb, GFP_ATOMIC);

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

static void ems_usb_rx_can_msg(struct ems_usb *dev, struct ems_cpc_msg *msg)
{
        struct can_frame *cf;
        struct sk_buff *skb;
        int i;
        struct net_device_stats *stats = &dev->netdev->stats;

        skb = alloc_can_skb(dev->netdev, &cf);
        if (skb == NULL)
                return;

        cf->can_id = le32_to_cpu(msg->msg.can_msg.id);
        cf->can_dlc = get_can_dlc(msg->msg.can_msg.length & 0xF);

        if (msg->type == CPC_MSG_TYPE_EXT_CAN_FRAME ||
            msg->type == CPC_MSG_TYPE_EXT_RTR_FRAME)
                cf->can_id |= CAN_EFF_FLAG;

        if (msg->type == CPC_MSG_TYPE_RTR_FRAME ||
            msg->type == CPC_MSG_TYPE_EXT_RTR_FRAME) {
                cf->can_id |= CAN_RTR_FLAG;
        } else {
                for (i = 0; i < cf->can_dlc; i++)
                        cf->data[i] = msg->msg.can_msg.msg[i];
        }

        netif_rx(skb);

        stats->rx_packets++;
        stats->rx_bytes += cf->can_dlc;
}

static void ems_usb_rx_err(struct ems_usb *dev, struct ems_cpc_msg *msg)
{
        struct can_frame *cf;
        struct sk_buff *skb;
        struct net_device_stats *stats = &dev->netdev->stats;

        skb = alloc_can_err_skb(dev->netdev, &cf);
        if (skb == NULL)
                return;

        if (msg->type == CPC_MSG_TYPE_CAN_STATE) {
                u8 state = msg->msg.can_state;

                if (state & SJA1000_SR_BS) {
                        dev->can.state = CAN_STATE_BUS_OFF;
                        cf->can_id |= CAN_ERR_BUSOFF;

                        dev->can.can_stats.bus_off++;
                        can_bus_off(dev->netdev);
                } else if (state & SJA1000_SR_ES) {
                        dev->can.state = CAN_STATE_ERROR_WARNING;
                        dev->can.can_stats.error_warning++;
                } else {
                        dev->can.state = CAN_STATE_ERROR_ACTIVE;
                        dev->can.can_stats.error_passive++;
                }
        } else if (msg->type == CPC_MSG_TYPE_CAN_FRAME_ERROR) {
                u8 ecc = msg->msg.error.cc.regs.sja1000.ecc;
                u8 txerr = msg->msg.error.cc.regs.sja1000.txerr;
                u8 rxerr = msg->msg.error.cc.regs.sja1000.rxerr;

                /* bus error interrupt */
                dev->can.can_stats.bus_error++;
                stats->rx_errors++;

                cf->can_id |= CAN_ERR_PROT | CAN_ERR_BUSERROR;

                switch (ecc & SJA1000_ECC_MASK) {
                case SJA1000_ECC_BIT:
                        cf->data[2] |= CAN_ERR_PROT_BIT;
                        break;
                case SJA1000_ECC_FORM:
                        cf->data[2] |= CAN_ERR_PROT_FORM;
                        break;
                case SJA1000_ECC_STUFF:
                        cf->data[2] |= CAN_ERR_PROT_STUFF;
                        break;
                default:
                        cf->data[2] |= CAN_ERR_PROT_UNSPEC;
                        cf->data[3] = ecc & SJA1000_ECC_SEG;
                        break;
                }

                /* Error occurred during transmission? */
                if ((ecc & SJA1000_ECC_DIR) == 0)
                        cf->data[2] |= CAN_ERR_PROT_TX;

                if (dev->can.state == CAN_STATE_ERROR_WARNING ||
                    dev->can.state == CAN_STATE_ERROR_PASSIVE) {
                        cf->data[1] = (txerr > rxerr) ?
                            CAN_ERR_CRTL_TX_PASSIVE : CAN_ERR_CRTL_RX_PASSIVE;
                }
        } else if (msg->type == CPC_MSG_TYPE_OVERRUN) {
                cf->can_id |= CAN_ERR_CRTL;
                cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;

                stats->rx_over_errors++;
                stats->rx_errors++;
        }

        netif_rx(skb);

        stats->rx_packets++;
        stats->rx_bytes += cf->can_dlc;
}

/*
 * callback for bulk IN urb
 */
static void ems_usb_read_bulk_callback(struct urb *urb)
{
        struct ems_usb *dev = urb->context;
        struct net_device *netdev;
        int retval;

        netdev = dev->netdev;

        if (!netif_device_present(netdev))
                return;

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

        case -ENOENT:
                return;

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

        if (urb->actual_length > CPC_HEADER_SIZE) {
                struct ems_cpc_msg *msg;
                u8 *ibuf = urb->transfer_buffer;
                u8 msg_count, start;

                msg_count = ibuf[0] & ~0x80;

                start = CPC_HEADER_SIZE;

                while (msg_count) {
                        msg = (struct ems_cpc_msg *)&ibuf[start];

                        switch (msg->type) {
                        case CPC_MSG_TYPE_CAN_STATE:
                                /* Process CAN state changes */
                                ems_usb_rx_err(dev, msg);
                                break;

                        case CPC_MSG_TYPE_CAN_FRAME:
                        case CPC_MSG_TYPE_EXT_CAN_FRAME:
                        case CPC_MSG_TYPE_RTR_FRAME:
                        case CPC_MSG_TYPE_EXT_RTR_FRAME:
                                ems_usb_rx_can_msg(dev, msg);
                                break;

                        case CPC_MSG_TYPE_CAN_FRAME_ERROR:
                                /* Process errorframe */
                                ems_usb_rx_err(dev, msg);
                                break;

                        case CPC_MSG_TYPE_OVERRUN:
                                /* Message lost while receiving */
                                ems_usb_rx_err(dev, msg);
                                break;
                        }

                        start += CPC_MSG_HEADER_LEN + msg->length;
                        msg_count--;

                        if (start > urb->transfer_buffer_length) {
                                netdev_err(netdev, "format error\n");
                                break;
                        }
                }
        }

resubmit_urb:
        usb_fill_bulk_urb(urb, dev->udev, usb_rcvbulkpipe(dev->udev, 2),
                          urb->transfer_buffer, RX_BUFFER_SIZE,
                          ems_usb_read_bulk_callback, dev);

        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 for bulk IN urb
 */
static void ems_usb_write_bulk_callback(struct urb *urb)
{
        struct ems_tx_urb_context *context = urb->context;
        struct ems_usb *dev;
        struct net_device *netdev;

        BUG_ON(!context);

        dev = context->dev;
        netdev = dev->netdev;

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

        atomic_dec(&dev->active_tx_urbs);

        if (!netif_device_present(netdev))
                return;

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

        netdev->trans_start = jiffies;

        /* transmission complete interrupt */
        netdev->stats.tx_packets++;
        netdev->stats.tx_bytes += context->dlc;

        can_get_echo_skb(netdev, context->echo_index);

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

        if (netif_queue_stopped(netdev))
                netif_wake_queue(netdev);
}

/*
 * Send the given CPC command synchronously
 */
static int ems_usb_command_msg(struct ems_usb *dev, struct ems_cpc_msg *msg)
{
        int actual_length;

        /* Copy payload */
        memcpy(&dev->tx_msg_buffer[CPC_HEADER_SIZE], msg,
               msg->length + CPC_MSG_HEADER_LEN);

        /* Clear header */
        memset(&dev->tx_msg_buffer[0], 0, CPC_HEADER_SIZE);

        return usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 2),
                            &dev->tx_msg_buffer[0],
                            msg->length + CPC_MSG_HEADER_LEN + CPC_HEADER_SIZE,
                            &actual_length, 1000);
}

/*
 * Change CAN controllers' mode register
 */
static int ems_usb_write_mode(struct ems_usb *dev, u8 mode)
{
        dev->active_params.msg.can_params.cc_params.sja1000.mode = mode;

        return ems_usb_command_msg(dev, &dev->active_params);
}

/*
 * Send a CPC_Control command to change behaviour when interface receives a CAN
 * message, bus error or CAN state changed notifications.
 */
static int ems_usb_control_cmd(struct ems_usb *dev, u8 val)
{
        struct ems_cpc_msg cmd;

        cmd.type = CPC_CMD_TYPE_CONTROL;
        cmd.length = CPC_MSG_HEADER_LEN + 1;

        cmd.msgid = 0;

        cmd.msg.generic[0] = val;

        return ems_usb_command_msg(dev, &cmd);
}

/*
 * Start interface
 */
static int ems_usb_start(struct ems_usb *dev)
{
        struct net_device *netdev = dev->netdev;
        int err, i;

        dev->intr_in_buffer[0] = 0;
        dev->free_slots = 15; /* initial size */

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

                /* create a URB, and a buffer for it */
                urb = usb_alloc_urb(0, GFP_KERNEL);
                if (!urb) {
                        netdev_err(netdev, "No memory left for URBs\n");
                        err = -ENOMEM;
                        break;
                }

                buf = usb_alloc_coherent(dev->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, dev->udev, usb_rcvbulkpipe(dev->udev, 2),
                                  buf, RX_BUFFER_SIZE,
                                  ems_usb_read_bulk_callback, dev);
                urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
                usb_anchor_urb(urb, &dev->rx_submitted);

                err = usb_submit_urb(urb, GFP_KERNEL);
                if (err) {
                        usb_unanchor_urb(urb);
                        usb_free_coherent(dev->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");

        /* Setup and start interrupt URB */
        usb_fill_int_urb(dev->intr_urb, dev->udev,
                         usb_rcvintpipe(dev->udev, 1),
                         dev->intr_in_buffer,
                         INTR_IN_BUFFER_SIZE,
                         ems_usb_read_interrupt_callback, dev, 1);

        err = usb_submit_urb(dev->intr_urb, GFP_KERNEL);
        if (err) {
                netdev_warn(netdev, "intr URB submit failed: %d\n", err);

                return err;
        }

        /* CPC-USB will transfer received message to host */
        err = ems_usb_control_cmd(dev, CONTR_CAN_MESSAGE | CONTR_CONT_ON);
        if (err)
                goto failed;

        /* CPC-USB will transfer CAN state changes to host */
        err = ems_usb_control_cmd(dev, CONTR_CAN_STATE | CONTR_CONT_ON);
        if (err)
                goto failed;

        /* CPC-USB will transfer bus errors to host */
        err = ems_usb_control_cmd(dev, CONTR_BUS_ERROR | CONTR_CONT_ON);
        if (err)
                goto failed;

        err = ems_usb_write_mode(dev, SJA1000_MOD_NORMAL);
        if (err)
                goto failed;

        dev->can.state = CAN_STATE_ERROR_ACTIVE;

        return 0;

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

        return err;
}

static void unlink_all_urbs(struct ems_usb *dev)
{
        int i;

        usb_unlink_urb(dev->intr_urb);

        usb_kill_anchored_urbs(&dev->rx_submitted);

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

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

static int ems_usb_open(struct net_device *netdev)
{
        struct ems_usb *dev = netdev_priv(netdev);
        int err;

        err = ems_usb_write_mode(dev, SJA1000_MOD_RM);
        if (err)
                return err;

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

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

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

                close_candev(netdev);

                return err;
        }


        netif_start_queue(netdev);

        return 0;
}

static netdev_tx_t ems_usb_start_xmit(struct sk_buff *skb, struct net_device *netdev)
{
        struct ems_usb *dev = netdev_priv(netdev);
        struct ems_tx_urb_context *context = NULL;
        struct net_device_stats *stats = &netdev->stats;
        struct can_frame *cf = (struct can_frame *)skb->data;
        struct ems_cpc_msg *msg;
        struct urb *urb;
        u8 *buf;
        int i, err;
        size_t size = CPC_HEADER_SIZE + CPC_MSG_HEADER_LEN
                        + sizeof(struct cpc_can_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) {
                netdev_err(netdev, "No memory left for URBs\n");
                goto nomem;
        }

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

        msg = (struct ems_cpc_msg *)&buf[CPC_HEADER_SIZE];

        msg->msg.can_msg.id = cpu_to_le32(cf->can_id & CAN_ERR_MASK);
        msg->msg.can_msg.length = cf->can_dlc;

        if (cf->can_id & CAN_RTR_FLAG) {
                msg->type = cf->can_id & CAN_EFF_FLAG ?
                        CPC_CMD_TYPE_EXT_RTR_FRAME : CPC_CMD_TYPE_RTR_FRAME;

                msg->length = CPC_CAN_MSG_MIN_SIZE;
        } else {
                msg->type = cf->can_id & CAN_EFF_FLAG ?
                        CPC_CMD_TYPE_EXT_CAN_FRAME : CPC_CMD_TYPE_CAN_FRAME;

                for (i = 0; i < cf->can_dlc; i++)
                        msg->msg.can_msg.msg[i] = cf->data[i];

                msg->length = CPC_CAN_MSG_MIN_SIZE + cf->can_dlc;
        }

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

        /*
         * May never happen! When this happens we'd more URBs in flight as
         * allowed (MAX_TX_URBS).
         */
        if (!context) {
                usb_free_coherent(dev->udev, size, buf, urb->transfer_dma);
                usb_free_urb(urb);

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

                return NETDEV_TX_BUSY;
        }

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

        usb_fill_bulk_urb(urb, dev->udev, usb_sndbulkpipe(dev->udev, 2), buf,
                          size, ems_usb_write_bulk_callback, context);
        urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
        usb_anchor_urb(urb, &dev->tx_submitted);

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

        atomic_inc(&dev->active_tx_urbs);

        err = usb_submit_urb(urb, GFP_ATOMIC);
        if (unlikely(err)) {
                can_free_echo_skb(netdev, context->echo_index);

                usb_unanchor_urb(urb);
                usb_free_coherent(dev->udev, size, buf, urb->transfer_dma);
                dev_kfree_skb(skb);

                atomic_dec(&dev->active_tx_urbs);

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

                        stats->tx_dropped++;
                }
        } else {
                netdev->trans_start = jiffies;

                /* Slow down tx path */
                if (atomic_read(&dev->active_tx_urbs) >= MAX_TX_URBS ||
                    dev->free_slots < 5) {
                        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;

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

        return NETDEV_TX_OK;
}

static int ems_usb_close(struct net_device *netdev)
{
        struct ems_usb *dev = netdev_priv(netdev);

        /* Stop polling */
        unlink_all_urbs(dev);

        netif_stop_queue(netdev);

        /* Set CAN controller to reset mode */
        if (ems_usb_write_mode(dev, SJA1000_MOD_RM))
                netdev_warn(netdev, "couldn't stop device");

        close_candev(netdev);

        return 0;
}

static const struct net_device_ops ems_usb_netdev_ops = {
        .ndo_open = ems_usb_open,
        .ndo_stop = ems_usb_close,
        .ndo_start_xmit = ems_usb_start_xmit,
        .ndo_change_mtu = can_change_mtu,
};

static const struct can_bittiming_const ems_usb_bittiming_const = {
        .name = "ems_usb",
        .tseg1_min = 1,
        .tseg1_max = 16,
        .tseg2_min = 1,
        .tseg2_max = 8,
        .sjw_max = 4,
        .brp_min = 1,
        .brp_max = 64,
        .brp_inc = 1,
};

static int ems_usb_set_mode(struct net_device *netdev, enum can_mode mode)
{
        struct ems_usb *dev = netdev_priv(netdev);

        switch (mode) {
        case CAN_MODE_START:
                if (ems_usb_write_mode(dev, SJA1000_MOD_NORMAL))
                        netdev_warn(netdev, "couldn't start device");

                if (netif_queue_stopped(netdev))
                        netif_wake_queue(netdev);
                break;

        default:
                return -EOPNOTSUPP;
        }

        return 0;
}

static int ems_usb_set_bittiming(struct net_device *netdev)
{
        struct ems_usb *dev = netdev_priv(netdev);
        struct can_bittiming *bt = &dev->can.bittiming;
        u8 btr0, btr1;

        btr0 = ((bt->brp - 1) & 0x3f) | (((bt->sjw - 1) & 0x3) << 6);
        btr1 = ((bt->prop_seg + bt->phase_seg1 - 1) & 0xf) |
                (((bt->phase_seg2 - 1) & 0x7) << 4);
        if (dev->can.ctrlmode & CAN_CTRLMODE_3_SAMPLES)
                btr1 |= 0x80;

        netdev_info(netdev, "setting BTR0=0x%02x BTR1=0x%02x\n", btr0, btr1);

        dev->active_params.msg.can_params.cc_params.sja1000.btr0 = btr0;
        dev->active_params.msg.can_params.cc_params.sja1000.btr1 = btr1;

        return ems_usb_command_msg(dev, &dev->active_params);
}

static void init_params_sja1000(struct ems_cpc_msg *msg)
{
        struct cpc_sja1000_params *sja1000 =
                &msg->msg.can_params.cc_params.sja1000;

        msg->type = CPC_CMD_TYPE_CAN_PARAMS;
        msg->length = sizeof(struct cpc_can_params);
        msg->msgid = 0;

        msg->msg.can_params.cc_type = CPC_CC_TYPE_SJA1000;

        /* Acceptance filter open */
        sja1000->acc_code0 = 0x00;
        sja1000->acc_code1 = 0x00;
        sja1000->acc_code2 = 0x00;
        sja1000->acc_code3 = 0x00;

        /* Acceptance filter open */
        sja1000->acc_mask0 = 0xFF;
        sja1000->acc_mask1 = 0xFF;
        sja1000->acc_mask2 = 0xFF;
        sja1000->acc_mask3 = 0xFF;

        sja1000->btr0 = 0;
        sja1000->btr1 = 0;

        sja1000->outp_contr = SJA1000_DEFAULT_OUTPUT_CONTROL;
        sja1000->mode = SJA1000_MOD_RM;
}

/*
 * probe function for new CPC-USB devices
 */
static int ems_usb_probe(struct usb_interface *intf,
                         const struct usb_device_id *id)
{
        struct net_device *netdev;
        struct ems_usb *dev;
        int i, err = -ENOMEM;

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

        dev = netdev_priv(netdev);

        dev->udev = interface_to_usbdev(intf);
        dev->netdev = netdev;

        dev->can.state = CAN_STATE_STOPPED;
        dev->can.clock.freq = EMS_USB_ARM7_CLOCK;
        dev->can.bittiming_const = &ems_usb_bittiming_const;
        dev->can.do_set_bittiming = ems_usb_set_bittiming;
        dev->can.do_set_mode = ems_usb_set_mode;
        dev->can.ctrlmode_supported = CAN_CTRLMODE_3_SAMPLES;

        netdev->netdev_ops = &ems_usb_netdev_ops;

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

        init_usb_anchor(&dev->rx_submitted);

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

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

        dev->intr_urb = usb_alloc_urb(0, GFP_KERNEL);
        if (!dev->intr_urb) {
                dev_err(&intf->dev, "Couldn't alloc intr URB\n");
                goto cleanup_candev;
        }

        dev->intr_in_buffer = kzalloc(INTR_IN_BUFFER_SIZE, GFP_KERNEL);
        if (!dev->intr_in_buffer)
                goto cleanup_intr_urb;

        dev->tx_msg_buffer = kzalloc(CPC_HEADER_SIZE +
                                     sizeof(struct ems_cpc_msg), GFP_KERNEL);
        if (!dev->tx_msg_buffer)
                goto cleanup_intr_in_buffer;

        usb_set_intfdata(intf, dev);

        SET_NETDEV_DEV(netdev, &intf->dev);

        init_params_sja1000(&dev->active_params);

        err = ems_usb_command_msg(dev, &dev->active_params);
        if (err) {
                netdev_err(netdev, "couldn't initialize controller: %d\n", err);
                goto cleanup_tx_msg_buffer;
        }

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

        return 0;

cleanup_tx_msg_buffer:
        kfree(dev->tx_msg_buffer);

cleanup_intr_in_buffer:
        kfree(dev->intr_in_buffer);

cleanup_intr_urb:
        usb_free_urb(dev->intr_urb);

cleanup_candev:
        free_candev(netdev);

        return err;
}

/*
 * called by the usb core when the device is removed from the system
 */
static void ems_usb_disconnect(struct usb_interface *intf)
{
        struct ems_usb *dev = usb_get_intfdata(intf);

        usb_set_intfdata(intf, NULL);

        if (dev) {
                unregister_netdev(dev->netdev);
                free_candev(dev->netdev);

                unlink_all_urbs(dev);

                usb_free_urb(dev->intr_urb);

                kfree(dev->intr_in_buffer);
        }
}

/* usb specific object needed to register this driver with the usb subsystem */
static struct usb_driver ems_usb_driver = {
        .name = "ems_usb",
        .probe = ems_usb_probe,
        .disconnect = ems_usb_disconnect,
        .id_table = ems_usb_table,
};

module_usb_driver(ems_usb_driver);