text: /**
   * Generic USB driver for report based interrupt in/out devices
   * like LD Didactic's USB devices. LD Didactic's USB devices are
   * HID devices which do not use HID report definitons (they use
   * raw interrupt in and our reports only for communication).
   *
   * This driver uses a ring buffer for time critical reading of
   * interrupt in reports and provides read and write methods for
   * raw interrupt reports (similar to the Windows HID driver).
   * Devices based on the book USB COMPLETE by Jan Axelson may need
   * such a compatibility to the Windows HID driver.
   *
   * Copyright (C) 2005 Michael Hund <mhund@ld-didactic.de>
   *
   *	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; either version 2 of
   *	the License, or (at your option) any later version.
   *
   * Derived from Lego USB Tower driver
   * Copyright (C) 2003 David Glance <advidgsf@sourceforge.net>
   *		 2001-2004 Juergen Stuber <starblue@users.sourceforge.net>
   */
  
  #include <linux/kernel.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/mutex.h>
  
  #include <asm/uaccess.h>
  #include <linux/input.h>
  #include <linux/usb.h>
  #include <linux/poll.h>
  
  /* Define these values to match your devices */
  #define USB_VENDOR_ID_LD		0x0f11	/* USB Vendor ID of LD Didactic GmbH */
  #define USB_DEVICE_ID_LD_CASSY		0x1000	/* USB Product ID of CASSY-S modules with 8 bytes endpoint size */
  #define USB_DEVICE_ID_LD_CASSY2		0x1001	/* USB Product ID of CASSY-S modules with 64 bytes endpoint size */
  #define USB_DEVICE_ID_LD_POCKETCASSY	0x1010	/* USB Product ID of Pocket-CASSY */
  #define USB_DEVICE_ID_LD_POCKETCASSY2	0x1011	/* USB Product ID of Pocket-CASSY 2 (reserved) */
  #define USB_DEVICE_ID_LD_MOBILECASSY	0x1020	/* USB Product ID of Mobile-CASSY */
  #define USB_DEVICE_ID_LD_MOBILECASSY2	0x1021	/* USB Product ID of Mobile-CASSY 2 (reserved) */
  #define USB_DEVICE_ID_LD_MICROCASSYVOLTAGE	0x1031	/* USB Product ID of Micro-CASSY Voltage */
  #define USB_DEVICE_ID_LD_MICROCASSYCURRENT	0x1032	/* USB Product ID of Micro-CASSY Current */
  #define USB_DEVICE_ID_LD_MICROCASSYTIME		0x1033	/* USB Product ID of Micro-CASSY Time (reserved) */
  #define USB_DEVICE_ID_LD_MICROCASSYTEMPERATURE	0x1035	/* USB Product ID of Micro-CASSY Temperature */
  #define USB_DEVICE_ID_LD_MICROCASSYPH		0x1038	/* USB Product ID of Micro-CASSY pH */
  #define USB_DEVICE_ID_LD_POWERANALYSERCASSY	0x1040	/* USB Product ID of Power Analyser CASSY */
  #define USB_DEVICE_ID_LD_CONVERTERCONTROLLERCASSY	0x1042	/* USB Product ID of Converter Controller CASSY */
  #define USB_DEVICE_ID_LD_MACHINETESTCASSY	0x1043	/* USB Product ID of Machine Test CASSY */
  #define USB_DEVICE_ID_LD_JWM		0x1080	/* USB Product ID of Joule and Wattmeter */
  #define USB_DEVICE_ID_LD_DMMP		0x1081	/* USB Product ID of Digital Multimeter P (reserved) */
  #define USB_DEVICE_ID_LD_UMIP		0x1090	/* USB Product ID of UMI P */
  #define USB_DEVICE_ID_LD_UMIC		0x10A0	/* USB Product ID of UMI C */
  #define USB_DEVICE_ID_LD_UMIB		0x10B0	/* USB Product ID of UMI B */
  #define USB_DEVICE_ID_LD_XRAY		0x1100	/* USB Product ID of X-Ray Apparatus 55481 */
  #define USB_DEVICE_ID_LD_XRAY2		0x1101	/* USB Product ID of X-Ray Apparatus 554800 */
  #define USB_DEVICE_ID_LD_XRAYCT		0x1110	/* USB Product ID of X-Ray Apparatus CT 554821*/
  #define USB_DEVICE_ID_LD_VIDEOCOM	0x1200	/* USB Product ID of VideoCom */
  #define USB_DEVICE_ID_LD_MOTOR		0x1210	/* USB Product ID of Motor (reserved) */
  #define USB_DEVICE_ID_LD_COM3LAB	0x2000	/* USB Product ID of COM3LAB */
  #define USB_DEVICE_ID_LD_TELEPORT	0x2010	/* USB Product ID of Terminal Adapter */
  #define USB_DEVICE_ID_LD_NETWORKANALYSER 0x2020	/* USB Product ID of Network Analyser */
  #define USB_DEVICE_ID_LD_POWERCONTROL	0x2030	/* USB Product ID of Converter Control Unit */
  #define USB_DEVICE_ID_LD_MACHINETEST	0x2040	/* USB Product ID of Machine Test System */
  #define USB_DEVICE_ID_LD_MOSTANALYSER	0x2050	/* USB Product ID of MOST Protocol Analyser */
  #define USB_DEVICE_ID_LD_MOSTANALYSER2	0x2051	/* USB Product ID of MOST Protocol Analyser 2 */
  #define USB_DEVICE_ID_LD_ABSESP		0x2060	/* USB Product ID of ABS ESP */
  #define USB_DEVICE_ID_LD_AUTODATABUS	0x2070	/* USB Product ID of Automotive Data Buses */
  #define USB_DEVICE_ID_LD_MCT		0x2080	/* USB Product ID of Microcontroller technique */
  #define USB_DEVICE_ID_LD_HYBRID		0x2090	/* USB Product ID of Automotive Hybrid */
  #define USB_DEVICE_ID_LD_HEATCONTROL	0x20A0	/* USB Product ID of Heat control */
  
  #ifdef CONFIG_USB_DYNAMIC_MINORS
  #define USB_LD_MINOR_BASE	0
  #else
  #define USB_LD_MINOR_BASE	176
  #endif
  
  /* table of devices that work with this driver */
  static const struct usb_device_id ld_usb_table[] = {
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_CASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_CASSY2) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_POCKETCASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_POCKETCASSY2) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MOBILECASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MOBILECASSY2) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MICROCASSYVOLTAGE) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MICROCASSYCURRENT) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MICROCASSYTIME) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MICROCASSYTEMPERATURE) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MICROCASSYPH) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_POWERANALYSERCASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_CONVERTERCONTROLLERCASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MACHINETESTCASSY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_JWM) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_DMMP) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_UMIP) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_UMIC) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_UMIB) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_XRAY) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_XRAY2) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_VIDEOCOM) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MOTOR) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_COM3LAB) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_TELEPORT) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_NETWORKANALYSER) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_POWERCONTROL) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MACHINETEST) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MOSTANALYSER) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MOSTANALYSER2) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_ABSESP) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_AUTODATABUS) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_MCT) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_HYBRID) },
  	{ USB_DEVICE(USB_VENDOR_ID_LD, USB_DEVICE_ID_LD_HEATCONTROL) },
  	{ }					/* Terminating entry */
  };
  MODULE_DEVICE_TABLE(usb, ld_usb_table);
  MODULE_VERSION("V0.14");
  MODULE_AUTHOR("Michael Hund <mhund@ld-didactic.de>");
  MODULE_DESCRIPTION("LD USB Driver");
  MODULE_LICENSE("GPL");
  MODULE_SUPPORTED_DEVICE("LD USB Devices");
  
  /* 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 = 128;
  module_param(ring_buffer_size, int, 0);
  MODULE_PARM_DESC(ring_buffer_size, "Read ring buffer size in reports");
  
  /* The write_buffer can contain more than one interrupt out transfer.
   */
  static int write_buffer_size = 10;
  module_param(write_buffer_size, int, 0);
  MODULE_PARM_DESC(write_buffer_size, "Write buffer size in reports");
  
  /* As of kernel version 2.6.4 ehci-hcd uses an
   * "only one interrupt transfer per frame" shortcut
   * to simplify the scheduling of periodic transfers.
   * This conflicts with our standard 1ms intervals for in and out URBs.
   * We use default intervals of 2ms for in and 2ms for out transfers,
   * which should be fast enough.
   * Increase the interval to allow more devices that do interrupt transfers,
   * or set to 1 to use the standard interval from the endpoint descriptors.
   */
  static int min_interrupt_in_interval = 2;
  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 = 2;
  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 ld_usb {
  	struct mutex		mutex;		/* locks this structure */
  	struct usb_interface*	intf;		/* save off the usb interface pointer */
  	unsigned long		disconnected:1;
  
  	int			open_count;	/* number of times this port has been opened */
  
  	char*			ring_buffer;
  	unsigned int		ring_head;
  	unsigned int		ring_tail;
  
  	wait_queue_head_t	read_wait;
  	wait_queue_head_t	write_wait;
  
  	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;
  	int			buffer_overflow;
  	spinlock_t		rbsl;
  
  	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;
  };
  
  static struct usb_driver ld_usb_driver;
  
  /**
   *	ld_usb_abort_transfers
   *      aborts transfers and frees associated data structures
   */
  static void ld_usb_abort_transfers(struct ld_usb *dev)
  {
  	/* shutdown transfer */
  	if (dev->interrupt_in_running) {
  		dev->interrupt_in_running = 0;
  		usb_kill_urb(dev->interrupt_in_urb);
  	}
  	if (dev->interrupt_out_busy)
  		usb_kill_urb(dev->interrupt_out_urb);
  }
  
  /**
   *	ld_usb_delete
   */
  static void ld_usb_delete(struct ld_usb *dev)
  {
  	/* 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);
  }
  
  /**
   *	ld_usb_interrupt_in_callback
   */
  static void ld_usb_interrupt_in_callback(struct urb *urb)
  {
  	struct ld_usb *dev = urb->context;
  	size_t *actual_buffer;
  	unsigned int next_ring_head;
  	int status = urb->status;
  	int retval;
  
  	if (status) {
  		if (status == -ENOENT ||
  		    status == -ECONNRESET ||
  		    status == -ESHUTDOWN) {
  			goto exit;
  		} else {
  			dev_dbg(&dev->intf->dev,
  				"%s: nonzero status received: %d\n", __func__,
  				status);
  			spin_lock(&dev->rbsl);
  			goto resubmit; /* maybe we can recover */
  		}
  	}
  
  	spin_lock(&dev->rbsl);
  	if (urb->actual_length > 0) {
  		next_ring_head = (dev->ring_head+1) % ring_buffer_size;
  		if (next_ring_head != dev->ring_tail) {
  			actual_buffer = (size_t*)(dev->ring_buffer + dev->ring_head*(sizeof(size_t)+dev->interrupt_in_endpoint_size));
  			/* actual_buffer gets urb->actual_length + interrupt_in_buffer */
  			*actual_buffer = urb->actual_length;
  			memcpy(actual_buffer+1, dev->interrupt_in_buffer, urb->actual_length);
  			dev->ring_head = next_ring_head;
  			dev_dbg(&dev->intf->dev, "%s: received %d bytes\n",
  				__func__, urb->actual_length);
  		} else {
  			dev_warn(&dev->intf->dev,
  				 "Ring buffer overflow, %d bytes dropped\n",
  				 urb->actual_length);
  			dev->buffer_overflow = 1;
  		}
  	}
  
  resubmit:
  	/* resubmit if we're still running */
  	if (dev->interrupt_in_running && !dev->buffer_overflow) {
  		retval = usb_submit_urb(dev->interrupt_in_urb, GFP_ATOMIC);
  		if (retval) {
  			dev_err(&dev->intf->dev,
  				"usb_submit_urb failed (%d)\n", retval);
  			dev->buffer_overflow = 1;
  		}
  	}
  	spin_unlock(&dev->rbsl);
  exit:
  	dev->interrupt_in_done = 1;
  	wake_up_interruptible(&dev->read_wait);
  }
  
  /**
   *	ld_usb_interrupt_out_callback
   */
  static void ld_usb_interrupt_out_callback(struct urb *urb)
  {
  	struct ld_usb *dev = urb->context;
  	int status = urb->status;
  
  	/* sync/async unlink faults aren't errors */
  	if (status && !(status == -ENOENT ||
  			status == -ECONNRESET ||
  			status == -ESHUTDOWN))
  		dev_dbg(&dev->intf->dev,
  			"%s - nonzero write interrupt status received: %d\n",
  			__func__, status);
  
  	dev->interrupt_out_busy = 0;
  	wake_up_interruptible(&dev->write_wait);
  }
  
  /**
   *	ld_usb_open
   */
  static int ld_usb_open(struct inode *inode, struct file *file)
  {
  	struct ld_usb *dev;
  	int subminor;
  	int retval;
  	struct usb_interface *interface;
  
  	nonseekable_open(inode, file);
  	subminor = iminor(inode);
  
  	interface = usb_find_interface(&ld_usb_driver, subminor);
  
  	if (!interface) {
  		printk(KERN_ERR "%s - error, can't find device for minor %d\n",
  		       __func__, subminor);
  		return -ENODEV;
  	}
  
  	dev = usb_get_intfdata(interface);
  
  	if (!dev)
  		return -ENODEV;
  
  	/* lock this device */
  	if (mutex_lock_interruptible(&dev->mutex))
  		return -ERESTARTSYS;
  
  	/* 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;
  	dev->buffer_overflow = 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,
  			 ld_usb_interrupt_in_callback,
  			 dev,
  			 dev->interrupt_in_interval);
  
  	dev->interrupt_in_running = 1;
  	dev->interrupt_in_done = 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->mutex);
  
  	return retval;
  }
  
  /**
   *	ld_usb_release
   */
  static int ld_usb_release(struct inode *inode, struct file *file)
  {
  	struct ld_usb *dev;
  	int retval = 0;
  
  	dev = file->private_data;
  
  	if (dev == NULL) {
  		retval = -ENODEV;
  		goto exit;
  	}
  
  	mutex_lock(&dev->mutex);
  
  	if (dev->open_count != 1) {
  		retval = -ENODEV;
  		goto unlock_exit;
  	}
  	if (dev->disconnected) {
  		/* the device was unplugged before the file was released */
  		mutex_unlock(&dev->mutex);
  		/* unlock here as ld_usb_delete frees dev */
  		ld_usb_delete(dev);
  		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);
  	ld_usb_abort_transfers(dev);
  	dev->open_count = 0;
  
  unlock_exit:
  	mutex_unlock(&dev->mutex);
  
  exit:
  	return retval;
  }
  
  /**
   *	ld_usb_poll
   */
  static unsigned int ld_usb_poll(struct file *file, poll_table *wait)
  {
  	struct ld_usb *dev;
  	unsigned int mask = 0;
  
  	dev = file->private_data;
  
  	if (dev->disconnected)
  		return POLLERR | POLLHUP;
  
  	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;
  }
  
  /**
   *	ld_usb_read
   */
  static ssize_t ld_usb_read(struct file *file, char __user *buffer, size_t count,
  			   loff_t *ppos)
  {
  	struct ld_usb *dev;
  	size_t *actual_buffer;
  	size_t bytes_to_read;
  	int retval = 0;
  	int rv;
  
  	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->mutex)) {
  		retval = -ERESTARTSYS;
  		goto exit;
  	}
  
  	/* verify that the device wasn't unplugged */
  	if (dev->disconnected) {
  		retval = -ENODEV;
  		printk(KERN_ERR "ldusb: No device or device unplugged %d\n", retval);
  		goto unlock_exit;
  	}
  
  	/* wait for data */
  	spin_lock_irq(&dev->rbsl);
  	while (dev->ring_head == dev->ring_tail) {
  		dev->interrupt_in_done = 0;
  		spin_unlock_irq(&dev->rbsl);
  		if (file->f_flags & O_NONBLOCK) {
  			retval = -EAGAIN;
  			goto unlock_exit;
  		}
  		retval = wait_event_interruptible(dev->read_wait, dev->interrupt_in_done);
  		if (retval < 0)
  			goto unlock_exit;
  
  		spin_lock_irq(&dev->rbsl);
  	}
  	spin_unlock_irq(&dev->rbsl);
  
  	/* actual_buffer contains actual_length + interrupt_in_buffer */
  	actual_buffer = (size_t*)(dev->ring_buffer + dev->ring_tail*(sizeof(size_t)+dev->interrupt_in_endpoint_size));
  	if (*actual_buffer > dev->interrupt_in_endpoint_size) {
  		retval = -EIO;
  		goto unlock_exit;
  	}
  	bytes_to_read = min(count, *actual_buffer);
  	if (bytes_to_read < *actual_buffer)
  		dev_warn(&dev->intf->dev, "Read buffer overflow, %zd bytes dropped\n",
  			 *actual_buffer-bytes_to_read);
  
  	/* copy one interrupt_in_buffer from ring_buffer into userspace */
  	if (copy_to_user(buffer, actual_buffer+1, bytes_to_read)) {
  		retval = -EFAULT;
  		goto unlock_exit;
  	}
  	retval = bytes_to_read;
  
  	spin_lock_irq(&dev->rbsl);
  	dev->ring_tail = (dev->ring_tail + 1) % ring_buffer_size;
  
  	if (dev->buffer_overflow) {
  		dev->buffer_overflow = 0;
  		spin_unlock_irq(&dev->rbsl);
  		rv = usb_submit_urb(dev->interrupt_in_urb, GFP_KERNEL);
  		if (rv < 0)
  			dev->buffer_overflow = 1;
  	} else {
  		spin_unlock_irq(&dev->rbsl);
  	}
  
  unlock_exit:
  	/* unlock the device */
  	mutex_unlock(&dev->mutex);
  
  exit:
  	return retval;
  }
  
  /**
   *	ld_usb_write
   */
  static ssize_t ld_usb_write(struct file *file, const char __user *buffer,
  			    size_t count, loff_t *ppos)
  {
  	struct ld_usb *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->mutex)) {
  		retval = -ERESTARTSYS;
  		goto exit;
  	}
  
  	/* verify that the device wasn't unplugged */
  	if (dev->disconnected) {
  		retval = -ENODEV;
  		printk(KERN_ERR "ldusb: 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);
  	dev_dbg(&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) {
  		/* try HID_REQ_SET_REPORT=9 on control_endpoint instead of interrupt_out_endpoint */
  		retval = usb_control_msg(interface_to_usbdev(dev->intf),
  					 usb_sndctrlpipe(interface_to_usbdev(dev->intf), 0),
  					 9,
  					 USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_OUT,
  					 1 << 8, 0,
  					 dev->interrupt_out_buffer,
  					 bytes_to_write,
  					 USB_CTRL_SET_TIMEOUT);
  		if (retval < 0)
  			dev_err(&dev->intf->dev,
  				"Couldn't submit HID_REQ_SET_REPORT %d\n",
  				retval);
  		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,
  			 ld_usb_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->mutex);
  
  exit:
  	return retval;
  }
  
  /* file operations needed when we register this driver */
  static const struct file_operations ld_usb_fops = {
  	.owner =	THIS_MODULE,
  	.read  =	ld_usb_read,
  	.write =	ld_usb_write,
  	.open =		ld_usb_open,
  	.release =	ld_usb_release,
  	.poll =		ld_usb_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 ld_usb_class = {
  	.name =		"ldusb%d",
  	.fops =		&ld_usb_fops,
  	.minor_base =	USB_LD_MINOR_BASE,
  };
  
  /**
   *	ld_usb_probe
   *
   *	Called by the usb core when a new device is connected that it thinks
   *	this driver might be interested in.
   */
  static int ld_usb_probe(struct usb_interface *intf, const struct usb_device_id *id)
  {
  	struct usb_device *udev = interface_to_usbdev(intf);
  	struct ld_usb *dev = NULL;
  	struct usb_host_interface *iface_desc;
  	struct usb_endpoint_descriptor *endpoint;
  	char *buffer;
  	int i;
  	int retval = -ENOMEM;
  
  	/* allocate memory for our device state and initialize it */
  
  	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
  	if (!dev)
  		goto exit;
  	mutex_init(&dev->mutex);
  	spin_lock_init(&dev->rbsl);
  	dev->intf = intf;
  	init_waitqueue_head(&dev->read_wait);
  	init_waitqueue_head(&dev->write_wait);
  
  	/* workaround for early firmware versions on fast computers */
  	if ((le16_to_cpu(udev->descriptor.idVendor) == USB_VENDOR_ID_LD) &&
  	    ((le16_to_cpu(udev->descriptor.idProduct) == USB_DEVICE_ID_LD_CASSY) ||
  	     (le16_to_cpu(udev->descriptor.idProduct) == USB_DEVICE_ID_LD_COM3LAB)) &&
  	    (le16_to_cpu(udev->descriptor.bcdDevice) <= 0x103)) {
  		buffer = kmalloc(256, GFP_KERNEL);
  		if (!buffer)
  			goto error;
  		/* usb_string makes SETUP+STALL to leave always ControlReadLoop */
  		usb_string(udev, 255, buffer, 256);
  		kfree(buffer);
  	}
  
  	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 = usb_endpoint_maxp(dev->interrupt_in_endpoint);
  	dev->ring_buffer = kcalloc(ring_buffer_size,
  			sizeof(size_t) + dev->interrupt_in_endpoint_size,
  			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)
  		goto error;
  	dev->interrupt_out_endpoint_size = dev->interrupt_out_endpoint ? usb_endpoint_maxp(dev->interrupt_out_endpoint) :
  									 udev->descriptor.bMaxPacketSize0;
  	dev->interrupt_out_buffer = kmalloc(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)
  		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, &ld_usb_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, "LD USB Device #%d now attached to major %d minor %d\n",
  		(intf->minor - USB_LD_MINOR_BASE), USB_MAJOR, intf->minor);
  
  exit:
  	return retval;
  
  error:
  	ld_usb_delete(dev);
  
  	return retval;
  }
  
  /**
   *	ld_usb_disconnect
   *
   *	Called by the usb core when the device is removed from the system.
   */
  static void ld_usb_disconnect(struct usb_interface *intf)
  {
  	struct ld_usb *dev;
  	int minor;
  
  	dev = usb_get_intfdata(intf);
  	usb_set_intfdata(intf, NULL);
  
  	minor = intf->minor;
  
  	/* give back our minor */
  	usb_deregister_dev(intf, &ld_usb_class);
  
  	usb_poison_urb(dev->interrupt_in_urb);
  	usb_poison_urb(dev->interrupt_out_urb);
  
  	mutex_lock(&dev->mutex);
  
  	/* if the device is not opened, then we clean up right now */
  	if (!dev->open_count) {
  		mutex_unlock(&dev->mutex);
  		ld_usb_delete(dev);
  	} else {
  		dev->disconnected = 1;
  		/* wake up pollers */
  		wake_up_interruptible_all(&dev->read_wait);
  		wake_up_interruptible_all(&dev->write_wait);
  		mutex_unlock(&dev->mutex);
  	}
  
  	dev_info(&intf->dev, "LD USB Device #%d now disconnected\n",
  		 (minor - USB_LD_MINOR_BASE));
  }
  
  /* usb specific object needed to register this driver with the usb subsystem */
  static struct usb_driver ld_usb_driver = {
  	.name =		"ldusb",
  	.probe =	ld_usb_probe,
  	.disconnect =	ld_usb_disconnect,
  	.id_table =	ld_usb_table,
  };
  
  module_usb_driver(ld_usb_driver);
  
  