/*
 * Frontier Designs Tranzport driver
 *
 * Copyright (C) 2007 Michael Taht (m@taht.net)
 *
 * Based on the usbled driver and ldusb drivers by
 *
 * Copyright (C) 2004 Greg Kroah-Hartman (greg@kroah.com)
 * Copyright (C) 2005 Michael Hund <mhund@ld-didactic.de>
 *
 * The ldusb driver was, in turn, derived from Lego USB Tower driver
 * Copyright (C) 2003 David Glance <advidgsf@sourceforge.net>
 *               2001-2004 Juergen Stuber <starblue@users.sourceforge.net>
 *
 *      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.
 *
 */

/*
 * This driver uses a ring buffer for time critical reading of
 * interrupt in reports and provides read and write methods for
 * raw interrupt reports.
 */

/* Note: this currently uses a dumb ringbuffer for reads and writes.
 * A more optimal driver would cache and kill off outstanding urbs that are
 * now invalid, and ignore ones that already were in the queue but valid
 * as we only have 17 commands for the tranzport. In particular this is
 * key for getting lights to flash in time as otherwise many commands
 * can be buffered up before the light change makes it to the interface.
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/mutex.h>

#include <linux/uaccess.h>
#include <linux/input.h>
#include <linux/usb.h>
#include <linux/poll.h>

/* Define these values to match your devices */
#define VENDOR_ID   0x165b
#define PRODUCT_ID  0x8101

#ifdef CONFIG_USB_DYNAMIC_MINORS
#define USB_TRANZPORT_MINOR_BASE        0
#else  /* FIXME 177- is the another driver's minor - apply for a minor soon */
#define USB_TRANZPORT_MINOR_BASE        177
#endif

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

MODULE_DEVICE_TABLE(usb, usb_tranzport_table);
MODULE_VERSION("0.35");
MODULE_AUTHOR("Mike Taht <m@taht.net>");
MODULE_DESCRIPTION("Tranzport USB Driver");
MODULE_LICENSE("GPL");
MODULE_SUPPORTED_DEVICE("Frontier Designs Tranzport Control Surface");

#define SUPPRESS_EXTRA_OFFLINE_EVENTS 1
#define COMPRESS_WHEEL_EVENTS 1
#define BUFFERED_READS 1
#define RING_BUFFER_SIZE 1000
#define WRITE_BUFFER_SIZE 34
#define TRANZPORT_USB_TIMEOUT 10
#define TRANZPORT_DEBUG 0

static int debug = TRANZPORT_DEBUG;

/* Use our own dbg macro */
#define dbg_info(dev, format, arg...) do                        \
        { if (debug) dev_info(dev , format , ## arg); } while (0)

/* Module parameters */

module_param(debug, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug, "Debug enabled or not");

/*
 * All interrupt in transfers are collected in a ring buffer to
 * avoid racing conditions and get better performance of the driver.
 */

static int ring_buffer_size = RING_BUFFER_SIZE;

module_param(ring_buffer_size, int, S_IRUGO);
MODULE_PARM_DESC(ring_buffer_size, "Read ring buffer size in reports");

/*
 * The write_buffer can one day contain more than one interrupt out transfer.
 */
static int write_buffer_size = WRITE_BUFFER_SIZE;
module_param(write_buffer_size, int, S_IRUGO);
MODULE_PARM_DESC(write_buffer_size, "Write buffer size");

/*
 * Increase the interval for debugging purposes.
 * or set to 1 to use the standard interval from the endpoint descriptors.
 */

static int min_interrupt_in_interval = TRANZPORT_USB_TIMEOUT;
module_param(min_interrupt_in_interval, int, 0);
MODULE_PARM_DESC(min_interrupt_in_interval,
                "Minimum interrupt in interval in ms");

static int min_interrupt_out_interval = TRANZPORT_USB_TIMEOUT;
module_param(min_interrupt_out_interval, int, 0);
MODULE_PARM_DESC(min_interrupt_out_interval,
                "Minimum interrupt out interval in ms");

struct tranzport_cmd {
        unsigned char cmd[8];
};

/* Structure to hold all of our device specific stuff */

struct usb_tranzport {
        struct mutex mtx;       /* locks this structure */
        struct usb_interface *intf;     /* save off the usb interface pointer */
        int open_count;         /* number of times this port opened */
        struct tranzport_cmd (*ring_buffer)[RING_BUFFER_SIZE];
        unsigned int ring_head;
        unsigned int ring_tail;
        wait_queue_head_t read_wait;
        wait_queue_head_t write_wait;
        unsigned char *interrupt_in_buffer;
        struct usb_endpoint_descriptor *interrupt_in_endpoint;
        struct urb *interrupt_in_urb;
        int interrupt_in_interval;
        size_t interrupt_in_endpoint_size;
        int interrupt_in_running;
        int interrupt_in_done;
        char *interrupt_out_buffer;
        struct usb_endpoint_descriptor *interrupt_out_endpoint;
        struct urb *interrupt_out_urb;
        int interrupt_out_interval;
        size_t interrupt_out_endpoint_size;
        int interrupt_out_busy;

        /* Sysfs support */

        unsigned char enable;   /* 0 if disabled 1 if enabled */
        unsigned char offline;  /* if the device is out of range or asleep */
        unsigned char compress_wheel;   /* flag to compress wheel events */
};

/* prevent races between open() and disconnect() */
static DEFINE_MUTEX(disconnect_mutex);

static struct usb_driver usb_tranzport_driver;

/**
 *      usb_tranzport_abort_transfers
 *      aborts transfers and frees associated data structures
 */
static void usb_tranzport_abort_transfers(struct usb_tranzport *dev)
{
        /* shutdown transfer */
        if (dev->interrupt_in_running) {
                dev->interrupt_in_running = 0;
                if (dev->intf)
                        usb_kill_urb(dev->interrupt_in_urb);
        }
        if (dev->interrupt_out_busy)
                if (dev->intf)
                        usb_kill_urb(dev->interrupt_out_urb);
}

#define show_int(value) \
        static ssize_t show_##value(struct device *dev, \
                              struct device_attribute *attr, char *buf) \
        {       \
                struct usb_interface *intf = to_usb_interface(dev);     \
                struct usb_tranzport *t = usb_get_intfdata(intf);       \
                return sprintf(buf, "%d\n", t->value);  \
        }       \
        static DEVICE_ATTR(value, S_IRUGO, show_##value, NULL);

#define show_set_int(value)     \
        static ssize_t show_##value(struct device *dev, \
                              struct device_attribute *attr, char *buf) \
        {       \
                struct usb_interface *intf = to_usb_interface(dev);     \
                struct usb_tranzport *t = usb_get_intfdata(intf);       \
                return sprintf(buf, "%d\n", t->value);  \
        }       \
        static ssize_t set_##value(struct device *dev,  \
                             struct device_attribute *attr,             \
                             const char *buf, size_t count)             \
        {       \
                struct usb_interface *intf = to_usb_interface(dev);     \
                struct usb_tranzport *t = usb_get_intfdata(intf);       \
                unsigned long temp;     \
                if (kstrtoul(buf, 10, &temp))   \
                        return -EINVAL; \
                t->value = temp;        \
                return count;   \
        }       \
        static DEVICE_ATTR(value, S_IWUSR | S_IRUGO, show_##value, set_##value);

show_int(enable);
show_int(offline);
show_set_int(compress_wheel);

/**
 *      usb_tranzport_delete
 */
static void usb_tranzport_delete(struct usb_tranzport *dev)
{
        usb_tranzport_abort_transfers(dev);
        if (dev->intf != NULL) {
                device_remove_file(&dev->intf->dev, &dev_attr_enable);
                device_remove_file(&dev->intf->dev, &dev_attr_offline);
                device_remove_file(&dev->intf->dev, &dev_attr_compress_wheel);
        }

        /* free data structures */
        usb_free_urb(dev->interrupt_in_urb);
        usb_free_urb(dev->interrupt_out_urb);
        kfree(dev->ring_buffer);
        kfree(dev->interrupt_in_buffer);
        kfree(dev->interrupt_out_buffer);
        kfree(dev);
}

/**
 *      usb_tranzport_interrupt_in_callback
 */

static void usb_tranzport_interrupt_in_callback(struct urb *urb)
{
        struct usb_tranzport *dev = urb->context;
        unsigned int next_ring_head;
        int retval = -1;

        if (urb->status) {
                if (urb->status == -ENOENT ||
                        urb->status == -ECONNRESET ||
                        urb->status == -ESHUTDOWN) {
                        goto exit;
                } else {
                        dbg_info(&dev->intf->dev,
                                 "%s: nonzero status received: %d\n",
                                 __func__, urb->status);
                        goto resubmit;  /* maybe we can recover */
                }
        }

        if (urb->actual_length != 8) {
                dev_warn(&dev->intf->dev,
                        "Urb length was %d bytes!!"
                        "Do something intelligent\n",
                         urb->actual_length);
        } else {
                dbg_info(&dev->intf->dev,
                         "%s: received: %02x%02x%02x%02x%02x%02x%02x%02x\n",
                         __func__, dev->interrupt_in_buffer[0],
                         dev->interrupt_in_buffer[1],
                         dev->interrupt_in_buffer[2],
                         dev->interrupt_in_buffer[3],
                         dev->interrupt_in_buffer[4],
                         dev->interrupt_in_buffer[5],
                         dev->interrupt_in_buffer[6],
                         dev->interrupt_in_buffer[7]);
#if SUPPRESS_EXTRA_OFFLINE_EVENTS
        if (dev->offline == 2 && dev->interrupt_in_buffer[1] == 0xff)
                goto resubmit;
                if (dev->offline == 1 && dev->interrupt_in_buffer[1] == 0xff) {
                        dev->offline = 2;
                        goto resubmit;
                }

                /* Always pass one offline event up the stack */
                if (dev->offline > 0 && dev->interrupt_in_buffer[1] != 0xff)
                        dev->offline = 0;
                if (dev->offline == 0 && dev->interrupt_in_buffer[1] == 0xff)
                        dev->offline = 1;

#endif  /* SUPPRESS_EXTRA_OFFLINE_EVENTS */
           dbg_info(&dev->intf->dev, "%s: head, tail are %x, %x\n",
                __func__, dev->ring_head, dev->ring_tail);

                next_ring_head = (dev->ring_head + 1) % ring_buffer_size;

                if (next_ring_head != dev->ring_tail) {
                        memcpy(&((*dev->ring_buffer)[dev->ring_head]),
                               dev->interrupt_in_buffer, urb->actual_length);
                        dev->ring_head = next_ring_head;
                        retval = 0;
                        memset(dev->interrupt_in_buffer, 0, urb->actual_length);
                } else {
                        dev_warn(&dev->intf->dev,
                                 "Ring buffer overflow, %d bytes dropped\n",
                                 urb->actual_length);
                        memset(dev->interrupt_in_buffer, 0, urb->actual_length);
                }
        }

resubmit:
/* resubmit if we're still running */
        if (dev->interrupt_in_running && dev->intf) {
                retval = usb_submit_urb(dev->interrupt_in_urb, GFP_ATOMIC);
                if (retval)
                        dev_err(&dev->intf->dev,
                                "usb_submit_urb failed (%d)\n", retval);
        }

exit:
        dev->interrupt_in_done = 1;
        wake_up_interruptible(&dev->read_wait);
}

/**
 *      usb_tranzport_interrupt_out_callback
 */
static void usb_tranzport_interrupt_out_callback(struct urb *urb)
{
        struct usb_tranzport *dev = urb->context;
        /* sync/async unlink faults aren't errors */
        if (urb->status && !(urb->status == -ENOENT ||
                                urb->status == -ECONNRESET ||
                                urb->status == -ESHUTDOWN))
                dbg_info(&dev->intf->dev,
                        "%s - nonzero write interrupt status received: %d\n",
                        __func__, urb->status);

        dev->interrupt_out_busy = 0;
        wake_up_interruptible(&dev->write_wait);
}
/**
 *      usb_tranzport_open
 */
static int usb_tranzport_open(struct inode *inode, struct file *file)
{
        struct usb_tranzport *dev;
        int subminor;
        int retval = 0;
        struct usb_interface *interface;

        nonseekable_open(inode, file);
        subminor = iminor(inode);

        mutex_lock(&disconnect_mutex);

        interface = usb_find_interface(&usb_tranzport_driver, subminor);

        if (!interface) {
                pr_err("%s - error, can't find device for minor %d\n",
                       __func__, subminor);
                retval = -ENODEV;
                goto unlock_disconnect_exit;
        }

        dev = usb_get_intfdata(interface);

        if (!dev) {
                retval = -ENODEV;
                goto unlock_disconnect_exit;
        }

        /* lock this device */
        if (mutex_lock_interruptible(&dev->mtx)) {
                retval = -ERESTARTSYS;
                goto unlock_disconnect_exit;
        }

        /* allow opening only once */
        if (dev->open_count) {
                retval = -EBUSY;
                goto unlock_exit;
        }
        dev->open_count = 1;

        /* initialize in direction */
        dev->ring_head = 0;
        dev->ring_tail = 0;
        usb_fill_int_urb(dev->interrupt_in_urb,
                        interface_to_usbdev(interface),
                        usb_rcvintpipe(interface_to_usbdev(interface),
                                dev->interrupt_in_endpoint->
                                bEndpointAddress),
                        dev->interrupt_in_buffer,
                        dev->interrupt_in_endpoint_size,
                        usb_tranzport_interrupt_in_callback, dev,
                        dev->interrupt_in_interval);

        dev->interrupt_in_running = 1;
        dev->interrupt_in_done = 0;
        dev->enable = 1;
        dev->offline = 0;
        dev->compress_wheel = 1;

        retval = usb_submit_urb(dev->interrupt_in_urb, GFP_KERNEL);
        if (retval) {
                dev_err(&interface->dev,
                        "Couldn't submit interrupt_in_urb %d\n", retval);
                dev->interrupt_in_running = 0;
                dev->open_count = 0;
                goto unlock_exit;
        }

        /* save device in the file's private structure */
        file->private_data = dev;

unlock_exit:
        mutex_unlock(&dev->mtx);

unlock_disconnect_exit:
        mutex_unlock(&disconnect_mutex);

        return retval;
}

/**
 *      usb_tranzport_release
 */
static int usb_tranzport_release(struct inode *inode, struct file *file)
{
        struct usb_tranzport *dev;
        int retval = 0;

        dev = file->private_data;

        if (dev == NULL) {
                retval = -ENODEV;
                goto exit;
        }

        if (mutex_lock_interruptible(&dev->mtx)) {
                retval = -ERESTARTSYS;
                goto exit;
        }

        if (dev->open_count != 1) {
                retval = -ENODEV;
                goto unlock_exit;
        }

        if (dev->intf == NULL) {
                /* the device was unplugged before the file was released */
                mutex_unlock(&dev->mtx);
                /* unlock here as usb_tranzport_delete frees dev */
                usb_tranzport_delete(dev);
                retval = -ENODEV;
                goto exit;
        }

        /* wait until write transfer is finished */
        if (dev->interrupt_out_busy)
                wait_event_interruptible_timeout(dev->write_wait,
                                                !dev->interrupt_out_busy,
                                                2 * HZ);
        usb_tranzport_abort_transfers(dev);
        dev->open_count = 0;

unlock_exit:
        mutex_unlock(&dev->mtx);

exit:
        return retval;
}

/**
 *      usb_tranzport_poll
 */
static unsigned int usb_tranzport_poll(struct file *file, poll_table *wait)
{
        struct usb_tranzport *dev;
        unsigned int mask = 0;
        dev = file->private_data;
        poll_wait(file, &dev->read_wait, wait);
        poll_wait(file, &dev->write_wait, wait);
        if (dev->ring_head != dev->ring_tail)
                mask |= POLLIN | POLLRDNORM;
        if (!dev->interrupt_out_busy)
                mask |= POLLOUT | POLLWRNORM;
        return mask;
}
/**
 *      usb_tranzport_read
 */

static ssize_t usb_tranzport_read(struct file *file, char __user *buffer,
                                size_t count, loff_t *ppos)
{
        struct usb_tranzport *dev;
        int retval = 0;
#if BUFFERED_READS
        int c = 0;
#endif
#if COMPRESS_WHEEL_EVENTS
        signed char oldwheel;
        signed char newwheel;
        int cancompress = 1;
        int next_tail;
#endif

        /* do I have such a thing as a null event? */

        dev = file->private_data;

        /* verify that we actually have some data to read */
        if (count == 0)
                goto exit;

        /* lock this object */
        if (mutex_lock_interruptible(&dev->mtx)) {
                retval = -ERESTARTSYS;
                goto exit;
        }

        /* verify that the device wasn't unplugged */
        if (dev->intf == NULL) {
                retval = -ENODEV;
                pr_err("%s: No device or device unplugged %d\n",
                       __func__, retval);
                goto unlock_exit;
        }

        while (dev->ring_head == dev->ring_tail) {

                if (file->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto unlock_exit;
                }
                /* tiny race - FIXME: make atomic? */
                /* atomic_cmp_exchange(&dev->interrupt_in_done,0,0); */
                dev->interrupt_in_done = 0;
                retval = wait_event_interruptible(dev->read_wait,
                                                  dev->interrupt_in_done);
                if (retval < 0)
                        goto unlock_exit;
        }

        dbg_info(&dev->intf->dev,
                "%s: copying to userspace: "
                "%02x%02x%02x%02x%02x%02x%02x%02x\n",
                 __func__,
                 (*dev->ring_buffer)[dev->ring_tail].cmd[0],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[1],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[2],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[3],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[4],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[5],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[6],
                 (*dev->ring_buffer)[dev->ring_tail].cmd[7]);

#if BUFFERED_READS
        c = 0;
        while ((c < count) && (dev->ring_tail != dev->ring_head)) {

#if COMPRESS_WHEEL_EVENTS
                next_tail = (dev->ring_tail+1) % ring_buffer_size;
                if (dev->compress_wheel)
                        cancompress = 1;
                while (dev->ring_head != next_tail && cancompress == 1) {
                        newwheel = (*dev->ring_buffer)[next_tail].cmd[6];
                        oldwheel = (*dev->ring_buffer)[dev->ring_tail].cmd[6];
                        /* if both are wheel events, and
                         * no buttons have changes (FIXME, do I have to check?),
                         * and we are the same sign, we can compress +- 7F
                         */
                        dbg_info(&dev->intf->dev,
                                "%s: trying to compress: "
                                "%02x%02x%02x%02x%02x%02x%02x%02x\n",
                                __func__,
                                (*dev->ring_buffer)[dev->ring_tail].cmd[0],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[1],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[2],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[3],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[4],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[5],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[6],
                                (*dev->ring_buffer)[dev->ring_tail].cmd[7]);

                        if (((*dev->ring_buffer)[dev->ring_tail].cmd[6] != 0 &&
                                (*dev->ring_buffer)[next_tail].cmd[6] != 0) &&
                                ((newwheel > 0 && oldwheel > 0) ||
                                        (newwheel < 0 && oldwheel < 0)) &&
                                ((*dev->ring_buffer)[dev->ring_tail].cmd[2] ==
                                (*dev->ring_buffer)[next_tail].cmd[2]) &&
                                ((*dev->ring_buffer)[dev->ring_tail].cmd[3] ==
                                (*dev->ring_buffer)[next_tail].cmd[3]) &&
                                ((*dev->ring_buffer)[dev->ring_tail].cmd[4] ==
                                (*dev->ring_buffer)[next_tail].cmd[4]) &&
                                ((*dev->ring_buffer)[dev->ring_tail].cmd[5] ==
                                (*dev->ring_buffer)[next_tail].cmd[5])) {
                                dbg_info(&dev->intf->dev,
                                        "%s: should compress: "
                                        "%02x%02x%02x%02x%02x%02x%02x%02x\n",
                                        __func__,
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[0],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[1],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[2],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[3],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[4],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[5],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[6],
                                        (*dev->ring_buffer)[dev->ring_tail].
                                        cmd[7]);
                                newwheel += oldwheel;
                                if (oldwheel > 0 && !(newwheel > 0)) {
                                        newwheel = 0x7f;
                                        cancompress = 0;
                                }
                                if (oldwheel < 0 && !(newwheel < 0)) {
                                        newwheel = 0x80;
                                        cancompress = 0;
                                }

                                (*dev->ring_buffer)[next_tail].cmd[6] =
                                        newwheel;
                                dev->ring_tail = next_tail;
                                next_tail =
                                        (dev->ring_tail + 1) % ring_buffer_size;
                        } else {
                                cancompress = 0;
                        }
                }
#endif /* COMPRESS_WHEEL_EVENTS */
                if (copy_to_user(
                                &buffer[c],
                                &(*dev->ring_buffer)[dev->ring_tail], 8)) {
                        retval = -EFAULT;
                        goto unlock_exit;
                }
                dev->ring_tail = (dev->ring_tail + 1) % ring_buffer_size;
                c += 8;
                dbg_info(&dev->intf->dev,
                         "%s: head, tail are %x, %x\n",
                         __func__, dev->ring_head, dev->ring_tail);
        }
        retval = c;

#else
/*  if (copy_to_user(buffer, &(*dev->ring_buffer)[dev->ring_tail], 8)) { */
        retval = -EFAULT;
        goto unlock_exit;
}

dev->ring_tail = (dev->ring_tail + 1) % ring_buffer_size;
dbg_info(&dev->intf->dev, "%s: head, tail are %x, %x\n",
         __func__, dev->ring_head, dev->ring_tail);

retval = 8;
#endif /* BUFFERED_READS */

unlock_exit:
/* unlock the device */
mutex_unlock(&dev->mtx);

exit:
return retval;
}

/**
 *      usb_tranzport_write
 */
static ssize_t usb_tranzport_write(struct file *file,
                                const char __user *buffer, size_t count,
                                loff_t *ppos)
{
        struct usb_tranzport *dev;
        size_t bytes_to_write;
        int retval = 0;

        dev = file->private_data;

        /* verify that we actually have some data to write */
        if (count == 0)
                goto exit;

        /* lock this object */
        if (mutex_lock_interruptible(&dev->mtx)) {
                retval = -ERESTARTSYS;
                goto exit;
        }
        /* verify that the device wasn't unplugged */
        if (dev->intf == NULL) {
                retval = -ENODEV;
                pr_err("%s: No device or device unplugged %d\n",
                       __func__, retval);
                goto unlock_exit;
        }

        /* wait until previous transfer is finished */
        if (dev->interrupt_out_busy) {
                if (file->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto unlock_exit;
                }
                retval = wait_event_interruptible(dev->write_wait,
                                                !dev->interrupt_out_busy);
                if (retval < 0)
                        goto unlock_exit;
        }

        /* write the data into interrupt_out_buffer from userspace */
        bytes_to_write = min(count,
                        write_buffer_size *
                        dev->interrupt_out_endpoint_size);
        if (bytes_to_write < count)
                dev_warn(&dev->intf->dev,
                        "Write buffer overflow, %zd bytes dropped\n",
                        count - bytes_to_write);

        dbg_info(&dev->intf->dev,
                "%s: count = %zd, bytes_to_write = %zd\n", __func__,
                count, bytes_to_write);

        if (copy_from_user(dev->interrupt_out_buffer, buffer, bytes_to_write)) {
                retval = -EFAULT;
                goto unlock_exit;
        }

        if (dev->interrupt_out_endpoint == NULL) {
                dev_err(&dev->intf->dev, "Endpoint should not be null!\n");
                goto unlock_exit;
        }

        /* send off the urb */
        usb_fill_int_urb(dev->interrupt_out_urb,
                        interface_to_usbdev(dev->intf),
                        usb_sndintpipe(interface_to_usbdev(dev->intf),
                                dev->interrupt_out_endpoint->
                                bEndpointAddress),
                        dev->interrupt_out_buffer, bytes_to_write,
                        usb_tranzport_interrupt_out_callback, dev,
                        dev->interrupt_out_interval);

        dev->interrupt_out_busy = 1;
        wmb();

        retval = usb_submit_urb(dev->interrupt_out_urb, GFP_KERNEL);
        if (retval) {
                dev->interrupt_out_busy = 0;
                dev_err(&dev->intf->dev,
                        "Couldn't submit interrupt_out_urb %d\n", retval);
                goto unlock_exit;
        }
        retval = bytes_to_write;

unlock_exit:
        /* unlock the device */
        mutex_unlock(&dev->mtx);

exit:
        return retval;
}

/* file operations needed when we register this driver */
static const struct file_operations usb_tranzport_fops = {
        .owner = THIS_MODULE,
        .read = usb_tranzport_read,
        .write = usb_tranzport_write,
        .open = usb_tranzport_open,
        .release = usb_tranzport_release,
        .poll = usb_tranzport_poll,
        .llseek = no_llseek,
};

/*
 * usb class driver info in order to get a minor number from the usb core,
 * and to have the device registered with the driver core
 */
static struct usb_class_driver usb_tranzport_class = {
        .name = "tranzport%d",
        .fops = &usb_tranzport_fops,
        .minor_base = USB_TRANZPORT_MINOR_BASE,
};

/**
 *      usb_tranzport_probe
 *
 *      Called by the usb core when a new device is connected that it thinks
 *      this driver might be interested in.
 */
static int usb_tranzport_probe(struct usb_interface *intf,
                               const struct usb_device_id *id) {
        struct usb_device *udev = interface_to_usbdev(intf);
        struct usb_tranzport *dev = NULL;
        struct usb_host_interface *iface_desc;
        struct usb_endpoint_descriptor *endpoint;
        int i;
        int true_size;
        int retval = -ENOMEM;

        /* allocate memory for our device state and initialize it */

         dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (dev == NULL)
                goto exit;

        mutex_init(&dev->mtx);
        dev->intf = intf;
        init_waitqueue_head(&dev->read_wait);
        init_waitqueue_head(&dev->write_wait);

        iface_desc = intf->cur_altsetting;

        /* set up the endpoint information */
        for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
                endpoint = &iface_desc->endpoint[i].desc;

                if (usb_endpoint_is_int_in(endpoint))
                        dev->interrupt_in_endpoint = endpoint;

                if (usb_endpoint_is_int_out(endpoint))
                        dev->interrupt_out_endpoint = endpoint;
        }
        if (dev->interrupt_in_endpoint == NULL) {
                dev_err(&intf->dev, "Interrupt in endpoint not found\n");
                goto error;
        }
        if (dev->interrupt_out_endpoint == NULL)
                dev_warn(&intf->dev,
                        "Interrupt out endpoint not found"
                        "(using control endpoint instead)\n");

        dev->interrupt_in_endpoint_size =
            le16_to_cpu(dev->interrupt_in_endpoint->wMaxPacketSize);

        if (dev->interrupt_in_endpoint_size != 8)
                dev_warn(&intf->dev, "Interrupt in endpoint size is not 8!\n");

        if (ring_buffer_size == 0)
                ring_buffer_size = RING_BUFFER_SIZE;
        true_size = min(ring_buffer_size, RING_BUFFER_SIZE);

        /*
         * FIXME - there are more usb_alloc routines for dma correctness.
         * Needed?
         */

        dev->ring_buffer =
            kmalloc((true_size * sizeof(struct tranzport_cmd)) + 8, GFP_KERNEL);
        if (!dev->ring_buffer)
                goto error;

        dev->interrupt_in_buffer =
            kmalloc(dev->interrupt_in_endpoint_size, GFP_KERNEL);
        if (!dev->interrupt_in_buffer)
                goto error;

        dev->interrupt_in_urb = usb_alloc_urb(0, GFP_KERNEL);
        if (!dev->interrupt_in_urb) {
                dev_err(&intf->dev, "Couldn't allocate interrupt_in_urb\n");
                goto error;
        }
        dev->interrupt_out_endpoint_size =
            dev->interrupt_out_endpoint ?
            le16_to_cpu(dev->interrupt_out_endpoint->wMaxPacketSize) :
            udev->descriptor.bMaxPacketSize0;

        if (dev->interrupt_out_endpoint_size != 8)
                dev_warn(&intf->dev,
                         "Interrupt out endpoint size is not 8!)\n");

        dev->interrupt_out_buffer =
                kmalloc_array(write_buffer_size,
                              dev->interrupt_out_endpoint_size, GFP_KERNEL);
        if (!dev->interrupt_out_buffer)
                goto error;

        dev->interrupt_out_urb = usb_alloc_urb(0, GFP_KERNEL);
        if (!dev->interrupt_out_urb) {
                dev_err(&intf->dev, "Couldn't allocate interrupt_out_urb\n");
                goto error;
        }
        dev->interrupt_in_interval =
            min_interrupt_in_interval >
            dev->interrupt_in_endpoint->bInterval ? min_interrupt_in_interval
            : dev->interrupt_in_endpoint->bInterval;

        if (dev->interrupt_out_endpoint) {
                dev->interrupt_out_interval =
                    min_interrupt_out_interval >
                    dev->interrupt_out_endpoint->bInterval ?
                    min_interrupt_out_interval :
                    dev->interrupt_out_endpoint->bInterval;
        }

        /* we can register the device now, as it is ready */
        usb_set_intfdata(intf, dev);

        retval = usb_register_dev(intf, &usb_tranzport_class);
        if (retval) {
                /* something prevented us from registering this driver */
                dev_err(&intf->dev,
                        "Not able to get a minor for this device.\n");
                usb_set_intfdata(intf, NULL);
                goto error;
        }

        retval = device_create_file(&intf->dev, &dev_attr_compress_wheel);
        if (retval)
                goto error;
        retval = device_create_file(&intf->dev, &dev_attr_enable);
        if (retval)
                goto error;
        retval = device_create_file(&intf->dev, &dev_attr_offline);
        if (retval)
                goto error;

        /* let the user know what node this device is now attached to */
        dev_info(&intf->dev,
                "Tranzport Device #%d now attached to major %d minor %d\n",
                (intf->minor - USB_TRANZPORT_MINOR_BASE), USB_MAJOR,
                intf->minor);

exit:
        return retval;

error:
        usb_tranzport_delete(dev);
        return retval;
}

/**
 *      usb_tranzport_disconnect
 *
 *      Called by the usb core when the device is removed from the system.
 */
static void usb_tranzport_disconnect(struct usb_interface *intf)
{
        struct usb_tranzport *dev;
        int minor;
        mutex_lock(&disconnect_mutex);
        dev = usb_get_intfdata(intf);
        usb_set_intfdata(intf, NULL);
        mutex_lock(&dev->mtx);
        minor = intf->minor;
        /* give back our minor */
        usb_deregister_dev(intf, &usb_tranzport_class);

        /* if the device is not opened, then we clean up right now */
        if (!dev->open_count) {
                mutex_unlock(&dev->mtx);
                usb_tranzport_delete(dev);
        } else {
                dev->intf = NULL;
                mutex_unlock(&dev->mtx);
        }

        mutex_unlock(&disconnect_mutex);

        dev_info(&intf->dev, "Tranzport Surface #%d now disconnected\n",
                (minor - USB_TRANZPORT_MINOR_BASE));
}

/* usb specific object needed to register this driver with the usb subsystem */
static struct usb_driver usb_tranzport_driver = {
        .name = "tranzport",
        .probe = usb_tranzport_probe,
        .disconnect = usb_tranzport_disconnect,
        .id_table = usb_tranzport_table,
};

module_usb_driver(usb_tranzport_driver);