Contributors: 21
Author Tokens Token Proportion Commits Commit Proportion
Michael Hund 2978 86.87% 4 10.26%
Oliver Neukum 176 5.13% 3 7.69%
Johan Hovold 95 2.77% 6 15.38%
Greg Kroah-Hartman 47 1.37% 7 17.95%
Karsten Koop 42 1.23% 1 2.56%
Daniel Walker 27 0.79% 1 2.56%
Sebastian Andrzej Siewior 13 0.38% 1 2.56%
Alan Stern 12 0.35% 1 2.56%
Linus Torvalds 7 0.20% 2 5.13%
Arnd Bergmann 5 0.15% 1 2.56%
Harvey Harrison 5 0.15% 1 2.56%
Milian Reichardt 4 0.12% 1 2.56%
Kees Cook 3 0.09% 1 2.56%
Arjan van de Ven 3 0.09% 1 2.56%
Al Viro 2 0.06% 1 2.56%
Luiz Fernando N. Capitulino 2 0.06% 2 5.13%
Wolfram Sang 2 0.06% 1 2.56%
Kuninori Morimoto 2 0.06% 1 2.56%
Kirill Smelkov 1 0.03% 1 2.56%
Márton Németh 1 0.03% 1 2.56%
Uwe Kleine-König 1 0.03% 1 2.56%
Total 3428 39 


// SPDX-License-Identifier: GPL-2.0+
/**
 * 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>
 *
 * 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 <linux/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_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, 0000);
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, 0000);
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, 0000);
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, 0000);
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;
	unsigned long flags;
	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_irqsave(&dev->rbsl, flags);
			goto resubmit; /* maybe we can recover */
		}
	}

	spin_lock_irqsave(&dev->rbsl, flags);
	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_irqrestore(&dev->rbsl, flags);
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;

	stream_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 __poll_t ld_usb_poll(struct file *file, poll_table *wait)
{
	struct ld_usb *dev;
	__poll_t mask = 0;

	dev = file->private_data;

	if (dev->disconnected)
		return EPOLLERR | EPOLLHUP;

	poll_wait(file, &dev->read_wait, wait);
	poll_wait(file, &dev->write_wait, wait);

	if (dev->ring_head != dev->ring_tail)
		mask |= EPOLLIN | EPOLLRDNORM;
	if (!dev->interrupt_out_busy)
		mask |= EPOLLOUT | EPOLLWRNORM;

	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, %zu 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, %zu bytes dropped\n",
			count - bytes_to_write);
	dev_dbg(&dev->intf->dev, "%s: count = %zu, bytes_to_write = %zu\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;
	char *buffer;
	int retval = -ENOMEM;
	int res;

	/* 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;

	res = usb_find_last_int_in_endpoint(iface_desc,
			&dev->interrupt_in_endpoint);
	if (res) {
		dev_err(&intf->dev, "Interrupt in endpoint not found\n");
		retval = res;
		goto error;
	}

	res = usb_find_last_int_out_endpoint(iface_desc,
			&dev->interrupt_out_endpoint);
	if (res)
		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_array(write_buffer_size,
			      dev->interrupt_out_endpoint_size, GFP_KERNEL);
	if (!dev->interrupt_out_buffer)
		goto error;
	dev->interrupt_out_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->interrupt_out_urb)
		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);