/*
 * Frontier Designs Alphatrack 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 30 commands for the alphatrack. 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/kobject.h>
#include <linux/mutex.h>

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

#include "alphatrack.h"

#define VENDOR_ID       0x165b
#define PRODUCT_ID      0xfad1

#ifdef CONFIG_USB_DYNAMIC_MINORS
#define USB_ALPHATRACK_MINOR_BASE       0
#else
/* FIXME 176 - is another driver's minor - apply for that */
#define USB_ALPHATRACK_MINOR_BASE       176
#endif

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

MODULE_DEVICE_TABLE(usb, usb_alphatrack_table);
MODULE_VERSION("0.41");
MODULE_AUTHOR("Mike Taht <m@taht.net>");
MODULE_DESCRIPTION("Alphatrack USB Driver");
MODULE_LICENSE("GPL");
MODULE_SUPPORTED_DEVICE("Frontier Designs Alphatrack Control Surface");

/* These aren't done yet */

#define SUPPRESS_EXTRA_ONLINE_EVENTS 0
#define BUFFERED_WRITES 0
#define SUPPRESS_EXTRA_OFFLINE_EVENTS 0
#define COMPRESS_FADER_EVENTS 0

#define BUFFERED_READS 1
#define RING_BUFFER_SIZE 512
#define WRITE_BUFFER_SIZE 34
#define ALPHATRACK_USB_TIMEOUT 10
#define OUTPUT_CMD_SIZE 8
#define INPUT_CMD_SIZE 12
#define ALPHATRACK_DEBUG 0

static int debug = ALPHATRACK_DEBUG;

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

#define alphatrack_ocmd_info(dev, cmd, format, arg...)

#define alphatrack_icmd_info(dev, cmd, format, arg...)

/* 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");

/* 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 = ALPHATRACK_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 = ALPHATRACK_USB_TIMEOUT;
module_param(min_interrupt_out_interval, int, 0);
MODULE_PARM_DESC(min_interrupt_out_interval,
                 "Minimum interrupt out interval in ms");

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

struct usb_alphatrack {
        struct mutex mtx;       /* locks this structure */
        struct usb_interface *intf;     /* save off the usb interface pointer */
        int open_count;         /* number of times this port has been opened */

        /* make gcc happy */
        struct alphatrack_icmd (*ring_buffer)[RING_BUFFER_SIZE];
        struct alphatrack_ocmd (*write_buffer)[WRITE_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;
        unsigned char *oldi_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;

        atomic_t writes_pending;
        int event;              /* alternate interface to events */
        int fader;              /* 10 bits */
        int lights;             /* 23 bits */
        unsigned char dump_state;       /* 0 if disabled 1 if enabled */
        unsigned char enable;   /* 0 if disabled 1 if enabled */
        unsigned char offline;  /* if the device is out of range or asleep */
        unsigned char verbose;  /* be verbose in error reporting */
        unsigned char last_cmd[OUTPUT_CMD_SIZE];
        unsigned char screen[32];
};

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

/* forward declaration */

static struct usb_driver usb_alphatrack_driver;

/**
 *      usb_alphatrack_abort_transfers
 *      aborts transfers and frees associated data structures
 */
static void usb_alphatrack_abort_transfers(struct usb_alphatrack *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);
}

/**
 *      usb_alphatrack_delete
 */
static void usb_alphatrack_delete(struct usb_alphatrack *dev)
{
        usb_alphatrack_abort_transfers(dev);
        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);             /* fixme oldi_buffer */
}

/**
 *      usb_alphatrack_interrupt_in_callback
 */

static void usb_alphatrack_interrupt_in_callback(struct urb *urb)
{
        struct usb_alphatrack *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 != INPUT_CMD_SIZE) {
                dev_warn(&dev->intf->dev,
                         "Urb length was %d bytes!!"
                         "Do something intelligent\n", urb->actual_length);
        } else {
                alphatrack_ocmd_info(&dev->intf->dev,
                                     &(*dev->ring_buffer)[dev->ring_tail].cmd,
                                     "%s", "bla");
                if (memcmp
                    (dev->interrupt_in_buffer, dev->oldi_buffer,
                     INPUT_CMD_SIZE) == 0) {
                        goto resubmit;
                }
                memcpy(dev->oldi_buffer, dev->interrupt_in_buffer,
                       INPUT_CMD_SIZE);

#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
                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_alphatrack_interrupt_out_callback
 */
static void usb_alphatrack_interrupt_out_callback(struct urb *urb)
{
        struct usb_alphatrack *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);
        atomic_dec(&dev->writes_pending);
        dev->interrupt_out_busy = 0;
        wake_up_interruptible(&dev->write_wait);
}

/**
 *      usb_alphatrack_open
 */
static int usb_alphatrack_open(struct inode *inode, struct file *file)
{
        struct usb_alphatrack *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_alphatrack_driver, subminor);

        if (!interface) {
                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_alphatrack_interrupt_in_callback, dev,
                         dev->interrupt_in_interval);

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

        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_alphatrack_release
 */
static int usb_alphatrack_release(struct inode *inode, struct file *file)
{
        struct usb_alphatrack *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_alphatrack_delete frees dev */
                usb_alphatrack_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_alphatrack_abort_transfers(dev);
        dev->open_count = 0;

unlock_exit:
        mutex_unlock(&dev->mtx);

exit:
        return retval;
}

/**
 *      usb_alphatrack_poll
 */
static unsigned int usb_alphatrack_poll(struct file *file, poll_table * wait)
{
        struct usb_alphatrack *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_alphatrack_read
 */
static ssize_t usb_alphatrack_read(struct file *file, char __user *buffer,
                                   size_t count, loff_t *ppos)
{
        struct usb_alphatrack *dev;
        int retval = 0;

        int c = 0;

        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;
                err("No device or device unplugged %d\n", retval);
                goto unlock_exit;
        }

        while (dev->ring_head == dev->ring_tail) {
                if (file->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto unlock_exit;
                }
                dev->interrupt_in_done = 0;
                retval =
                    wait_event_interruptible(dev->read_wait,
                                             dev->interrupt_in_done);
                if (retval < 0)
                        goto unlock_exit;
        }

        alphatrack_ocmd_info(&dev->intf->dev,
                             &(*dev->ring_buffer)[dev->ring_tail].cmd, "%s",
                             ": copying to userspace");

        c = 0;
        while ((c < count) && (dev->ring_tail != dev->ring_head)) {
                if (copy_to_user
                    (&buffer[c], &(*dev->ring_buffer)[dev->ring_tail],
                     INPUT_CMD_SIZE)) {
                        retval = -EFAULT;
                        goto unlock_exit;
                }
                dev->ring_tail = (dev->ring_tail + 1) % ring_buffer_size;
                c += INPUT_CMD_SIZE;
                dbg_info(&dev->intf->dev, "%s: head, tail are %x, %x\n",
                         __func__, dev->ring_head, dev->ring_tail);
        }
        retval = c;

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

exit:
        return retval;
}

/**
 *      usb_alphatrack_write
 */
static ssize_t usb_alphatrack_write(struct file *file,
                                    const char __user *buffer, size_t count,
                                    loff_t *ppos)
{
        struct usb_alphatrack *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;
                err("No device or device unplugged %d\n", 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 */
        /* FIXME - if you write more than 12 bytes this breaks */
        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) {
                err("Endpoint should not be 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_alphatrack_interrupt_out_callback, dev,
                         dev->interrupt_out_interval);
        dev->interrupt_out_busy = 1;
        atomic_inc(&dev->writes_pending);
        wmb();

        retval = usb_submit_urb(dev->interrupt_out_urb, GFP_KERNEL);
        if (retval) {
                dev->interrupt_out_busy = 0;
                err("Couldn't submit interrupt_out_urb %d\n", retval);
                atomic_dec(&dev->writes_pending);
                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_alphatrack_fops = {
        .owner = THIS_MODULE,
        .read = usb_alphatrack_read,
        .write = usb_alphatrack_write,
        .open = usb_alphatrack_open,
        .release = usb_alphatrack_release,
        .poll = usb_alphatrack_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_alphatrack_class = {
        .name = "alphatrack%d",
        .fops = &usb_alphatrack_fops,
        .minor_base = USB_ALPHATRACK_MINOR_BASE,
};

/**
 *      usb_alphatrack_probe
 *
 *      Called by the usb core when a new device is connected that it thinks
 *      this driver might be interested in.
 */
static int usb_alphatrack_probe(struct usb_interface *intf,
                                const struct usb_device_id *id)
{
        struct usb_device *udev = interface_to_usbdev(intf);
        struct usb_alphatrack *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) {
                dev_err(&intf->dev, "Out of memory\n");
                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 != 64)
                dev_warn(&intf->dev, "Interrupt in endpoint size is not 64!\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 alphatrack_icmd)), GFP_KERNEL);

        if (!dev->ring_buffer) {
                dev_err(&intf->dev,
                        "Couldn't allocate input ring_buffer of size %d\n",
                        true_size);
                goto error;
        }

        dev->interrupt_in_buffer =
            kmalloc(dev->interrupt_in_endpoint_size, GFP_KERNEL);

        if (!dev->interrupt_in_buffer) {
                dev_err(&intf->dev, "Couldn't allocate interrupt_in_buffer\n");
                goto error;
        }
        dev->oldi_buffer = kmalloc(dev->interrupt_in_endpoint_size, GFP_KERNEL);
        if (!dev->oldi_buffer) {
                dev_err(&intf->dev, "Couldn't allocate old buffer\n");
                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 != 64)
                dev_warn(&intf->dev,
                         "Interrupt out endpoint size is not 64!)\n");

        if (write_buffer_size == 0)
                write_buffer_size = WRITE_BUFFER_SIZE;
        true_size = min(write_buffer_size, WRITE_BUFFER_SIZE);

        dev->interrupt_out_buffer =
            kmalloc(true_size * dev->interrupt_out_endpoint_size, GFP_KERNEL);

        if (!dev->interrupt_out_buffer) {
                dev_err(&intf->dev, "Couldn't allocate interrupt_out_buffer\n");
                goto error;
        }

        dev->write_buffer =
            kmalloc(true_size * sizeof(struct alphatrack_ocmd), GFP_KERNEL);

        if (!dev->write_buffer) {
                dev_err(&intf->dev, "Couldn't allocate write_buffer\n");
                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);

        atomic_set(&dev->writes_pending, 0);
        retval = usb_register_dev(intf, &usb_alphatrack_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;
        }

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

exit:
        return retval;

error:
        usb_alphatrack_delete(dev);

        return retval;
}

/**
 *      usb_alphatrack_disconnect
 *
 *      Called by the usb core when the device is removed from the system.
 */
static void usb_alphatrack_disconnect(struct usb_interface *intf)
{
        struct usb_alphatrack *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_alphatrack_class);

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

        atomic_set(&dev->writes_pending, 0);
        mutex_unlock(&disconnect_mutex);

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

/* usb specific object needed to register this driver with the usb subsystem */
static struct usb_driver usb_alphatrack_driver = {
        .name = "alphatrack",
        .probe = usb_alphatrack_probe,
        .disconnect = usb_alphatrack_disconnect,
        .id_table = usb_alphatrack_table,
};

/**
 *      usb_alphatrack_init
 */
static int __init usb_alphatrack_init(void)
{
        int retval;

        /* register this driver with the USB subsystem */
        retval = usb_register(&usb_alphatrack_driver);
        if (retval)
                err("usb_register failed for the " __FILE__
                    " driver. Error number %d\n", retval);

        return retval;
}

/**
 *      usb_alphatrack_exit
 */
static void __exit usb_alphatrack_exit(void)
{
        /* deregister this driver with the USB subsystem */
        usb_deregister(&usb_alphatrack_driver);
}

module_init(usb_alphatrack_init);
module_exit(usb_alphatrack_exit);