kernel / drivers / staging / frontier / alphatrack.c

/*
 * Frontier Designs Alphatrack driver
 *
 * Copyright (C) 2007 Michael Taht ([e-mail])
 *
 * Based on the usbled driver and ldusb drivers by
 *
 * Copyright (C) 2004 Greg Kroah-Hartman ([e-mail])
 * Copyright (C) 2005 Michael Hund <[e-mail]>
 *
 * The ldusb driver was, in turn, derived from Lego USB Tower driver
 * Copyright (C) 2003 David Glance <[e-mail]>
 *		 2001-2004 Juergen Stuber <[e-mail]>
 *
 *	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/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 <[e-mail]>");
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->oldi_buffer);
	kfree(dev->write_buffer);
	kfree(dev);
}

/** 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) {
		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_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;
		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;
		}
		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;
		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 */
	/* 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) {
		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_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;
		dev_err(&dev->intf->dev,
			"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)
		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_array(true_size,
					 sizeof(struct alphatrack_icmd),
					 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->oldi_buffer = kmalloc(dev->interrupt_in_endpoint_size, GFP_KERNEL);
	if (!dev->oldi_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 != 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_array(true_size,
			      dev->interrupt_out_endpoint_size,
			      GFP_KERNEL);
	if (!dev->interrupt_out_buffer)
		goto error;

	dev->write_buffer = kmalloc_array(true_size,
					  sizeof(struct alphatrack_ocmd),
					  GFP_KERNEL);
	if (!dev->write_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);

	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 {
		atomic_set(&dev->writes_pending, 0);
		dev->intf = NULL;
		mutex_unlock(&dev->mtx);
	}

	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,
};

module_usb_driver(usb_alphatrack_driver);