/*
 * 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) {
		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;
		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;
		}
		/* 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;
		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 */
	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_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;
		err("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) {
		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 != 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) {
		dev_err(&intf->dev,
			"Couldn't allocate ring_buffer 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->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(write_buffer_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->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);