[PATCH] char: xillybus: Add driver for XillyUSB (Xillybus variant for USB)

[eli . billauer]

From: Eli Billauer <eli.billauer@xxxxxxxxx>

The XillyUSB driver is the USB variant for the Xillybus FPGA IP core.
Even though it presents a nearly identical API on the FPGA and host,
it's almost a complete rewrite of the driver: The framework for exchanging
data on a USB bus is fundamentally different from doing the same with a
PCIe interface, which leaves very little in common between the existing
driver and the new one for XillyUSB.

Signed-off-by: Eli Billauer <eli.billauer@xxxxxxxxx>
---
 drivers/char/xillybus/Kconfig    |   11 +
 drivers/char/xillybus/Makefile   |    1 +
 drivers/char/xillybus/xillyusb.c | 2363 ++++++++++++++++++++++++++++++
 3 files changed, 2375 insertions(+)
 create mode 100644 drivers/char/xillybus/xillyusb.c

diff --git a/drivers/char/xillybus/Kconfig b/drivers/char/xillybus/Kconfig
index 130dbdce858f..18fa99ec1029 100644
--- a/drivers/char/xillybus/Kconfig
+++ b/drivers/char/xillybus/Kconfig
@@ -32,3 +32,14 @@ config XILLYBUS_OF
 	  system, say M.
 
 endif # if XILLYBUS
+
+config XILLYUSB
+	tristate "XillyUSB: Xillybus generic FPGA interface for USB"
+	depends on USB
+	select CRC32
+	help
+	  XillyUSB is the Xillybus variant which uses USB for communicating
+	  with the FPGA.
+
+	  Set to M if you want Xillybus to use USB for communicating with
+	  the FPGA.
diff --git a/drivers/char/xillybus/Makefile b/drivers/char/xillybus/Makefile
index 099e9a3585fc..57471fb61a12 100644
--- a/drivers/char/xillybus/Makefile
+++ b/drivers/char/xillybus/Makefile
@@ -6,3 +6,4 @@
 obj-$(CONFIG_XILLYBUS)		+= xillybus_core.o
 obj-$(CONFIG_XILLYBUS_PCIE)	+= xillybus_pcie.o
 obj-$(CONFIG_XILLYBUS_OF)	+= xillybus_of.o
+obj-$(CONFIG_XILLYUSB)		+= xillyusb.o
diff --git a/drivers/char/xillybus/xillyusb.c b/drivers/char/xillybus/xillyusb.c
new file mode 100644
index 000000000000..58f007e742e3
--- /dev/null
+++ b/drivers/char/xillybus/xillyusb.c
@@ -0,0 +1,2363 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2020 Xillybus Ltd, http://xillybus.com
+ *
+ * Driver for the XillyUSB FPGA/host framework.
+ *
+ * This driver interfaces with a special IP core in an FPGA, setting up
+ * a pipe between a hardware FIFO in the programmable logic and a device
+ * file in the host. The number of such pipes and their attributes are
+ * set up on the logic. This driver detects these automatically and
+ * creates the device files accordingly.
+ */
+
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <asm/byteorder.h>
+#include <linux/io.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/cdev.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+#include <linux/atomic.h>
+#include <linux/workqueue.h>
+#include <linux/crc32.h>
+#include <linux/poll.h>
+#include <linux/delay.h>
+#include <linux/usb.h>
+
+MODULE_DESCRIPTION("Driver for XillyUSB FPGA IP Core");
+MODULE_AUTHOR("Eli Billauer, Xillybus Ltd.");
+MODULE_VERSION("1.0");
+MODULE_ALIAS("xillyusb");
+MODULE_LICENSE("GPL v2");
+
+#define XILLY_RX_TIMEOUT (10 * HZ / 1000)
+#define XILLY_RESPONSE_TIMEOUT (500 * HZ / 1000)
+
+#define MAX_XILLYUSB_DEVS 64
+#define BUF_SIZE_ORDER 4
+#define BUFNUM 8
+#define LOG2_IDT_FIFO_SIZE 16
+#define LOG2_INITIAL_FIFO_BUF_SIZE 16
+
+#define MSG_EP_NUM 1
+#define IN_EP_NUM 1
+
+static const char xillyname[] = "xillyusb";
+/* err_name is used in log messages, where dev_err() might fail */
+static const char *err_name = xillyname;
+
+static struct class *xillyusb_class;
+
+static char xdev_map[MAX_XILLYUSB_DEVS];
+/* xdev_mutex is spinlock style: Taken last and for quick operations. */
+static DEFINE_MUTEX(xdev_mutex);
+static LIST_HEAD(xdev_list);
+
+static unsigned int fifo_buf_order;
+
+#define USB_VENDOR_ID_XILINX		0x03fd
+#define USB_VENDOR_ID_ALTERA		0x09fb
+
+#define USB_PRODUCT_ID_XILLYUSB		0xebbe
+
+static const struct usb_device_id xillyusb_table[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_XILINX, USB_PRODUCT_ID_XILLYUSB) },
+	{ USB_DEVICE(USB_VENDOR_ID_ALTERA, USB_PRODUCT_ID_XILLYUSB) },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, xillyusb_table);
+
+struct xillyusb_dev;
+
+struct xillyfifo {
+	unsigned int bufsize; /* In bytes, always a power of 2 */
+	unsigned int bufnum;
+	unsigned int size; /* Lazy: Equals bufsize * bufnum */
+	unsigned int buf_order;
+	atomic_t fill; /* Number of bytes in the FIFO */
+	wait_queue_head_t waitq;
+	unsigned int readpos;
+	unsigned int readbuf;
+	unsigned int writepos;
+	unsigned int writebuf;
+	void **mem;
+};
+
+struct xillyusb_channel;
+
+struct xillyusb_endpoint {
+	struct xillyusb_dev *xdev;
+
+	struct list_head buffers;
+	struct list_head filled_buffers;
+	spinlock_t buffers_lock; /* protect these two lists */
+
+	unsigned int order;
+	unsigned int buffer_size;
+
+	unsigned int fill_mask;
+
+	int outstanding_urbs;
+
+	struct usb_anchor anchor;
+
+	struct xillyfifo fifo;
+
+	struct work_struct workitem;
+	bool shutting_down;
+
+	u8 ep_num;
+};
+
+struct xillyusb_channel {
+	struct xillyusb_dev *xdev;
+
+	struct xillyfifo *in_fifo;
+	struct xillyusb_endpoint *out_ep;
+	struct mutex lock; /* protect @out_ep and @in_fifo */
+
+	struct mutex in_mutex; /* serialize fops on FPGA to host stream */
+	struct mutex out_mutex; /* serialize fops on host to FPGA stream */
+	wait_queue_head_t flushq;
+
+	int chan_idx;
+
+	u32 in_consumed_bytes;
+	u32 in_current_checkpoint;
+	u32 out_bytes;
+
+	unsigned int in_log2_element_size;
+	unsigned int out_log2_element_size;
+	unsigned int in_log2_fifo_size;
+	unsigned int out_log2_fifo_size;
+
+	unsigned int read_data_ok; /* EOF not arrived (yet) */
+	unsigned int poll_used;
+	unsigned int flushing;
+	unsigned int flushed;
+	unsigned int canceled;
+
+	/* Bit fields protected by xdev_mutex except for initialization */
+	unsigned readable:1;
+	unsigned writable:1;
+	unsigned open_for_read:1;
+	unsigned open_for_write:1;
+	unsigned in_synchronous:1;
+	unsigned out_synchronous:1;
+	unsigned in_seekable:1;
+	unsigned out_seekable:1;
+};
+
+struct xillybuffer {
+	struct list_head entry;
+	struct xillyusb_endpoint *ep;
+	void *buf;
+	unsigned int len;
+};
+
+struct xillyusb_dev {
+	struct xillyusb_channel *channels;
+
+	struct usb_device	*udev;
+	struct usb_interface	*interface;
+	struct kref		kref;
+	struct mutex		io_mutex; /* synchronize I/O with disconnect */
+	struct list_head	list_entry;
+	struct workqueue_struct	*workq;
+
+	int error;
+	spinlock_t error_lock; /* protect @error */
+	struct work_struct wakeup_workitem;
+
+	int index;
+	struct cdev *cdev;
+	int major;
+	int lowest_minor;
+	int num_channels;
+
+	struct xillyusb_endpoint *msg_ep;
+	struct xillyusb_endpoint *in_ep;
+
+	struct mutex msg_mutex; /* serialize opcode transmission */
+	int in_bytes_left;
+	int leftover_chan_num;
+	unsigned int in_counter;
+	struct mutex process_in_mutex; /* synchronize wakeup_all() */
+};
+
+/* FPGA to host opcodes */
+enum {
+	OPCODE_DATA = 0,
+	OPCODE_QUIESCE_ACK = 1,
+	OPCODE_EOF = 2,
+	OPCODE_REACHED_CHECKPOINT = 3,
+	OPCODE_CANCELED_CHECKPOINT = 4,
+};
+
+/* Host to FPGA opcodes */
+enum {
+	OPCODE_QUIESCE = 0,
+	OPCODE_REQ_IDT = 1,
+	OPCODE_SET_CHECKPOINT = 2,
+	OPCODE_CLOSE = 3,
+	OPCODE_SET_PUSH = 4,
+	OPCODE_UPDATE_PUSH = 5,
+	OPCODE_CANCEL_CHECKPOINT = 6,
+	OPCODE_SET_ADDR = 7,
+};
+
+/*
+ * fifo_write() and fifo_read() are NOT reentrant (i.e. concurrent multiple
+ * calls to each on the same FIFO is not allowed) however it's OK to have
+ * threads calling each of the two functions once on the same FIFO, and
+ * at the same time.
+ */
+
+static int fifo_write(struct xillyfifo *fifo,
+		      const void *data, unsigned int len,
+		      int (*copier)(void *, const void *, int))
+{
+	unsigned int done = 0;
+	unsigned int todo = len;
+	unsigned int nmax;
+	unsigned int writepos = fifo->writepos;
+	unsigned int writebuf = fifo->writebuf;
+
+	nmax = fifo->size - atomic_read(&fifo->fill);
+
+	while (1) {
+		unsigned int nrail = fifo->bufsize - writepos;
+		unsigned int n = min(todo, nmax);
+
+		if (n == 0) {
+			/*
+			 * Ensure copied data is visible before
+			 * it's accounted for.
+			 */
+			smp_wmb();
+			atomic_add(done, &fifo->fill);
+
+			fifo->writepos = writepos;
+			fifo->writebuf = writebuf;
+
+			return done;
+		}
+
+		if (n > nrail)
+			n = nrail;
+
+		if ((*copier)(fifo->mem[writebuf] + writepos, data + done, n))
+			return -EFAULT;
+
+		done += n;
+		todo -= n;
+
+		writepos += n;
+		nmax -= n;
+
+		if (writepos == fifo->bufsize) {
+			writepos = 0;
+			writebuf++;
+
+			if (writebuf == fifo->bufnum)
+				writebuf = 0;
+		}
+	}
+}
+
+static unsigned int fifo_read(struct xillyfifo *fifo,
+			      void *data, unsigned int len,
+			      int (*copier)(void *, const void *, int))
+{
+	unsigned int done = 0;
+	unsigned int todo = len;
+	unsigned int fill;
+	unsigned int readpos = fifo->readpos;
+	unsigned int readbuf = fifo->readbuf;
+
+	fill = atomic_read(&fifo->fill);
+
+	/* Ensure that the data accounted for is synchronized in buffer */
+	smp_rmb();
+
+	while (1) {
+		unsigned int nrail = fifo->bufsize - readpos;
+		unsigned int n = min(todo, fill);
+
+		if (n == 0) {
+			atomic_sub(done, &fifo->fill);
+
+			fifo->readpos = readpos;
+			fifo->readbuf = readbuf;
+
+			return done;
+		}
+
+		if (n > nrail)
+			n = nrail;
+
+		if ((*copier)(data + done, fifo->mem[readbuf] + readpos, n))
+			return -EFAULT;
+
+		done += n;
+		todo -= n;
+
+		readpos += n;
+		fill -= n;
+
+		if (readpos == fifo->bufsize) {
+			readpos = 0;
+			readbuf++;
+
+			if (readbuf == fifo->bufnum)
+				readbuf = 0;
+		}
+	}
+}
+
+static int fifo_init(struct xillyfifo *fifo,
+		     unsigned int log2_size)
+{
+	unsigned int log2_bufnum;
+	unsigned int buf_order;
+	int i;
+
+	unsigned int log2_fifo_buf_size;
+
+retry:
+	log2_fifo_buf_size = fifo_buf_order + PAGE_SHIFT;
+
+	if (log2_size > log2_fifo_buf_size) {
+		log2_bufnum = log2_size - log2_fifo_buf_size;
+		buf_order = fifo_buf_order;
+		fifo->bufsize = 1 << log2_fifo_buf_size;
+	} else {
+		log2_bufnum = 0;
+		buf_order = (log2_size > PAGE_SHIFT) ?
+			log2_size - PAGE_SHIFT : 0;
+		fifo->bufsize = 1 << log2_size;
+	}
+
+	fifo->bufnum = 1 << log2_bufnum;
+	fifo->size = fifo->bufnum * fifo->bufsize;
+	fifo->buf_order = buf_order;
+
+	fifo->mem = kmalloc_array(fifo->bufnum, sizeof(void *), GFP_KERNEL);
+
+	if (!fifo->mem)
+		return -ENOMEM;
+
+	for (i = 0; i < fifo->bufnum; i++) {
+		fifo->mem[i] = (void *)
+			__get_free_pages(GFP_KERNEL, buf_order);
+
+		if (!fifo->mem[i])
+			goto memfail;
+	}
+
+	atomic_set(&fifo->fill, 0);
+	fifo->readpos = 0;
+	fifo->readbuf = 0;
+	fifo->writepos = 0;
+	fifo->writebuf = 0;
+	init_waitqueue_head(&fifo->waitq);
+	return 0;
+
+memfail:
+	for (i--; i >= 0; i--)
+		free_pages((unsigned long)fifo->mem[i], buf_order);
+
+	kfree(fifo->mem);
+	fifo->mem = NULL;
+
+	if (fifo_buf_order) {
+		fifo_buf_order--;
+		pr_warn("%s: Trying again to allocate FIFO %d bytes, now with segments of %d bytes each\n",
+			err_name, 1 << log2_size,
+			1 << (fifo_buf_order + PAGE_SHIFT));
+		goto retry;
+	} else {
+		pr_err("%s: Failed to allocate FIFO with %d bytes, despite attepts to chop it into small pieces.\n",
+		       err_name, 1 << log2_size);
+		return -ENOMEM;
+	}
+}
+
+static void fifo_mem_release(struct xillyfifo *fifo)
+{
+	int i;
+
+	if (!fifo->mem)
+		return;
+
+	for (i = 0; i < fifo->bufnum; i++)
+		free_pages((unsigned long)fifo->mem[i], fifo->buf_order);
+
+	kfree(fifo->mem);
+}
+
+/*
+ * Note that endpoint_dealloc() also frees fifo memory (if allocated), even
+ * though endpoint_alloc doesn't allocate that memory.
+ */
+
+static void endpoint_dealloc(struct xillyusb_endpoint *ep)
+{
+	struct list_head *this, *next;
+	struct list_head *buffers = &ep->buffers;
+	unsigned int order = ep->order;
+
+	ep->shutting_down = true;
+
+	/*
+	 * The first cancel_work_sync() doesn't just cancel a possibly running
+	 * work item, but also ensures that if it's re-queued by a URB
+	 * completer in a race condition, the next execution of the work item
+	 * will see the ep->shutting_down as true, and do nothing. Hence we're
+	 * sure all queued URBs are anchored and no new ones will be added
+	 * after cancel_work_sync() returns.
+	 * However a second cancel_work_sync() is still required if such race
+	 * condition would re-queue the work item, since @ep is just about to
+	 * be freed.
+	 */
+
+	cancel_work_sync(&ep->workitem);
+	usb_kill_anchored_urbs(&ep->anchor);
+	cancel_work_sync(&ep->workitem);
+
+	fifo_mem_release(&ep->fifo);
+
+	list_for_each_safe(this, next, buffers) {
+		struct xillybuffer *xb =
+			list_entry(this, struct xillybuffer, entry);
+
+		free_pages((unsigned long)xb->buf, order);
+		kfree(xb);
+	}
+
+	kfree(ep);
+}
+
+static struct xillyusb_endpoint
+*endpoint_alloc(struct xillyusb_dev *xdev,
+		u8 ep_num,
+		void (*work)(struct work_struct *),
+		unsigned int order,
+		int bufnum)
+{
+	int i;
+
+	struct xillyusb_endpoint *ep;
+
+	ep = kzalloc(sizeof(*ep), GFP_KERNEL);
+
+	if (!ep)
+		return NULL;
+
+	INIT_LIST_HEAD(&ep->buffers);
+	INIT_LIST_HEAD(&ep->filled_buffers);
+
+	spin_lock_init(&ep->buffers_lock);
+
+	init_usb_anchor(&ep->anchor);
+	INIT_WORK(&ep->workitem, work);
+
+	ep->order = order;
+	ep->buffer_size =  1 << (PAGE_SHIFT + order);
+	ep->outstanding_urbs = 0;
+	ep->xdev = xdev;
+	ep->ep_num = ep_num;
+	ep->shutting_down = false;
+
+	for (i = 0; i < bufnum; i++) {
+		struct xillybuffer *xb;
+		unsigned long addr;
+
+		xb = kzalloc(sizeof(*xb), GFP_KERNEL);
+
+		if (!xb) {
+			endpoint_dealloc(ep);
+			return NULL;
+		}
+
+		addr = __get_free_pages(GFP_KERNEL, order);
+
+		if (!addr) {
+			kfree(xb);
+			endpoint_dealloc(ep);
+			return NULL;
+		}
+
+		xb->buf = (void *)addr;
+		xb->ep = ep;
+		list_add_tail(&xb->entry, &ep->buffers);
+	}
+	return ep;
+}
+
+static void cleanup_dev(struct kref *kref)
+{
+	struct xillyusb_dev *xdev =
+		container_of(kref, struct xillyusb_dev, kref);
+
+	if (xdev->in_ep)
+		endpoint_dealloc(xdev->in_ep);
+
+	if (xdev->msg_ep)
+		endpoint_dealloc(xdev->msg_ep);
+
+	if (xdev->workq)
+		destroy_workqueue(xdev->workq);
+
+	kfree(xdev->channels); /* Argument may be NULL, and that's fine */
+	kfree(xdev);
+}
+
+/*
+ * wakeup_all() is implemented as a work item, because of the need to be
+ * sure that bulk_in_work() sees xdev->error with a non-zero value if it
+ * runs after all read_data_ok have been cleared. xdev->error is assigned
+ * with this non-zero number prior to queueing the work, but it seems like
+ * only a mutex ensures this correct order of execution.
+ *
+ * In particular, the fact that wakeup_all() and bulk_in_work() are queued on
+ * the same workqueue makes their concurrent execution very unlikely,
+ * however the kernel's API doesn't seem to ensure this strictly.
+ * report_io_error() is possibly called in atomic context and can therefore
+ * not take a mutex.
+ */
+
+static void wakeup_all(struct work_struct *work)
+{
+	int i;
+	struct xillyusb_dev *xdev = container_of(work, struct xillyusb_dev,
+						 wakeup_workitem);
+
+	mutex_lock(&xdev->process_in_mutex);
+
+	for (i = 0; i < xdev->num_channels; i++) {
+		struct xillyusb_channel *chan = &xdev->channels[i];
+
+		mutex_lock(&chan->lock);
+
+		if (chan->in_fifo) {
+			/*
+			 * Fake an EOF: Even if such arrives, it won't be
+			 * processed.
+			 */
+			chan->read_data_ok = 0;
+			wake_up_interruptible(&chan->in_fifo->waitq);
+		}
+
+		if (chan->out_ep)
+			wake_up_interruptible(&chan->out_ep->fifo.waitq);
+
+		mutex_unlock(&chan->lock);
+
+		wake_up_interruptible(&chan->flushq);
+	}
+
+	mutex_unlock(&xdev->process_in_mutex);
+
+	wake_up_interruptible(&xdev->msg_ep->fifo.waitq);
+
+	kref_put(&xdev->kref, cleanup_dev);
+}
+
+static void report_io_error(struct xillyusb_dev *xdev,
+			    int errcode)
+{
+	unsigned long flags;
+	bool do_once = false;
+
+	spin_lock_irqsave(&xdev->error_lock, flags);
+	if (!xdev->error) {
+		xdev->error = errcode;
+		do_once = true;
+	}
+	spin_unlock_irqrestore(&xdev->error_lock, flags);
+
+	if (do_once) {
+		kref_get(&xdev->kref); /* xdev is used by work item */
+		queue_work(xdev->workq, &xdev->wakeup_workitem);
+	}
+}
+
+/*
+ * safely_assign_in_fifo() changes the value of chan->in_fifo and ensures
+ * the previous pointer is never used after its return.
+ */
+
+static void safely_assign_in_fifo(struct xillyusb_channel *chan,
+				  struct xillyfifo *fifo)
+{
+	mutex_lock(&chan->lock);
+	chan->in_fifo = fifo;
+	mutex_unlock(&chan->lock);
+
+	flush_work(&chan->xdev->in_ep->workitem);
+}
+
+static int xilly_memcpy(void *dst, const void *src, int n)
+{
+	memcpy(dst, src, n);
+	return 0;
+}
+
+static void bulk_in_completer(struct urb *urb)
+{
+	struct xillybuffer *xb = urb->context;
+	struct xillyusb_endpoint *ep = xb->ep;
+	unsigned long flags;
+
+	if (urb->status) {
+		if (!(urb->status == -ENOENT ||
+		      urb->status == -ECONNRESET ||
+		      urb->status == -ESHUTDOWN))
+			report_io_error(ep->xdev, -EIO);
+
+		spin_lock_irqsave(&ep->buffers_lock, flags);
+		list_add_tail(&xb->entry, &ep->buffers);
+		ep->outstanding_urbs--;
+		spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+		return;
+	}
+
+	xb->len = urb->actual_length;
+
+	spin_lock_irqsave(&ep->buffers_lock, flags);
+	list_add_tail(&xb->entry, &ep->filled_buffers);
+	spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+	if (!ep->shutting_down)
+		queue_work(ep->xdev->workq, &ep->workitem);
+}
+
+static void bulk_out_completer(struct urb *urb)
+{
+	struct xillybuffer *xb = urb->context;
+	struct xillyusb_endpoint *ep = xb->ep;
+	unsigned long flags;
+
+	if (urb->status &&
+	    (!(urb->status == -ENOENT ||
+	       urb->status == -ECONNRESET ||
+	       urb->status == -ESHUTDOWN)))
+		report_io_error(ep->xdev, -EIO);
+
+	spin_lock_irqsave(&ep->buffers_lock, flags);
+	list_add_tail(&xb->entry, &ep->buffers);
+	ep->outstanding_urbs--;
+	spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+	if (!ep->shutting_down)
+		queue_work(ep->xdev->workq, &ep->workitem);
+}
+
+static void try_queue_bulk_in(struct xillyusb_endpoint *ep)
+{
+	struct xillyusb_dev *xdev = ep->xdev;
+	struct xillybuffer *xb;
+	struct urb *urb;
+
+	int rc;
+	unsigned long flags;
+	unsigned int bufsize = ep->buffer_size;
+
+	if (ep->shutting_down)
+		return;
+
+	mutex_lock(&xdev->io_mutex);
+
+	if (!xdev->interface || xdev->error)
+		goto done;
+
+	while (1) {
+		spin_lock_irqsave(&ep->buffers_lock, flags);
+
+		if (list_empty(&ep->buffers)) {
+			spin_unlock_irqrestore(&ep->buffers_lock, flags);
+			goto done;
+		}
+
+		xb = list_first_entry(&ep->buffers, struct xillybuffer, entry);
+		list_del(&xb->entry);
+		ep->outstanding_urbs++;
+
+		spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+		urb = usb_alloc_urb(0, GFP_KERNEL);
+		if (!urb) {
+			report_io_error(xdev, -ENOMEM);
+			goto relist;
+		}
+
+		usb_fill_bulk_urb(urb, xdev->udev,
+				  usb_rcvbulkpipe(xdev->udev, ep->ep_num),
+				  xb->buf, bufsize, bulk_in_completer, xb);
+
+		usb_anchor_urb(urb, &ep->anchor);
+
+		rc = usb_submit_urb(urb, GFP_KERNEL);
+
+		if (rc) {
+			report_io_error(xdev, (rc == -ENOMEM) ? -ENOMEM :
+					-EIO);
+			goto unanchor;
+		}
+
+		usb_free_urb(urb); /* This just decrements reference count */
+	}
+
+unanchor:
+	usb_unanchor_urb(urb);
+	usb_free_urb(urb);
+
+relist:
+	spin_lock_irqsave(&ep->buffers_lock, flags);
+	list_add_tail(&xb->entry, &ep->buffers);
+	ep->outstanding_urbs--;
+	spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+done:
+	mutex_unlock(&xdev->io_mutex);
+}
+
+static void try_queue_bulk_out(struct xillyusb_endpoint *ep)
+{
+	struct xillyfifo *fifo = &ep->fifo;
+	struct xillyusb_dev *xdev = ep->xdev;
+	struct xillybuffer *xb;
+	struct urb *urb;
+
+	int rc;
+	unsigned int fill;
+	unsigned long flags;
+	bool submitted = false;
+
+	if (ep->shutting_down)
+		return;
+
+	mutex_lock(&xdev->io_mutex);
+
+	if (!xdev->interface || xdev->error)
+		goto done;
+
+	fill = atomic_read(&fifo->fill) & ep->fill_mask;
+
+	while (1) {
+		int count;
+		unsigned int max_read;
+
+		if (fill == 0)
+			goto done;
+
+		spin_lock_irqsave(&ep->buffers_lock, flags);
+
+		if ((fill < ep->buffer_size && ep->outstanding_urbs) ||
+		    list_empty(&ep->buffers)) {
+			spin_unlock_irqrestore(&ep->buffers_lock, flags);
+			goto done;
+		}
+
+		xb = list_first_entry(&ep->buffers, struct xillybuffer, entry);
+		list_del(&xb->entry);
+		ep->outstanding_urbs++;
+
+		spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+		max_read = min(fill, ep->buffer_size);
+
+		count = fifo_read(&ep->fifo, xb->buf, max_read, xilly_memcpy);
+
+		/*
+		 * xilly_memcpy always returns 0 => fifo_read can't fail =>
+		 * count > 0
+		 */
+
+		urb = usb_alloc_urb(0, GFP_KERNEL);
+		if (!urb) {
+			report_io_error(xdev, -ENOMEM);
+			goto relist;
+		}
+
+		usb_fill_bulk_urb(urb, xdev->udev,
+				  usb_sndbulkpipe(xdev->udev, ep->ep_num),
+				  xb->buf, count, bulk_out_completer, xb);
+
+		usb_anchor_urb(urb, &ep->anchor);
+
+		rc = usb_submit_urb(urb, GFP_KERNEL);
+
+		if (rc) {
+			report_io_error(xdev, (rc == -ENOMEM) ? -ENOMEM :
+					-EIO);
+			goto unanchor;
+		}
+
+		usb_free_urb(urb); /* This just decrements reference count */
+
+		fill -= count;
+		submitted = true;
+	}
+
+unanchor:
+	usb_unanchor_urb(urb);
+	usb_free_urb(urb);
+
+relist:
+	spin_lock_irqsave(&ep->buffers_lock, flags);
+	list_add_tail(&xb->entry, &ep->buffers);
+	ep->outstanding_urbs--;
+	spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+done:
+	mutex_unlock(&xdev->io_mutex);
+
+	if (submitted)
+		wake_up_interruptible(&fifo->waitq);
+}
+
+static void bulk_out_work(struct work_struct *work)
+{
+	struct xillyusb_endpoint *ep = container_of(work,
+						    struct xillyusb_endpoint,
+						    workitem);
+	try_queue_bulk_out(ep);
+}
+
+static int process_in_opcode(struct xillyusb_dev *xdev,
+			     int opcode,
+			     int chan_num)
+{
+	struct xillyusb_channel *chan;
+	int chan_idx = chan_num >> 1;
+
+	if (chan_idx >= xdev->num_channels) {
+		pr_err("%s: Received illegal channel ID %d from FPGA\n",
+		       err_name, chan_num);
+		return -EIO;
+	}
+
+	chan = &xdev->channels[chan_idx];
+
+	switch (opcode) {
+	case OPCODE_EOF:
+		if (!READ_ONCE(chan->read_data_ok)) {
+			pr_err("%s: Received unexpected EOF for channel %d\n",
+			       err_name, chan_num);
+			return -EIO;
+		}
+
+		/*
+		 * A write memory barrier ensures that the FIFO's fill level
+		 * is visible before read_data_ok turns zero, so the data in
+		 * the FIFO isn't missed by the consumer.
+		 */
+		smp_wmb();
+		WRITE_ONCE(chan->read_data_ok, 0);
+		wake_up_interruptible(&chan->in_fifo->waitq);
+		break;
+
+	case OPCODE_REACHED_CHECKPOINT:
+		chan->flushing = 0;
+		wake_up_interruptible(&chan->flushq);
+		break;
+
+	case OPCODE_CANCELED_CHECKPOINT:
+		chan->canceled = 1;
+		wake_up_interruptible(&chan->flushq);
+		break;
+
+	default:
+		pr_err("%s: Received illegal opcode %d from FPGA\n",
+		       err_name, opcode);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int process_bulk_in(struct xillybuffer *xb)
+{
+	struct xillyusb_endpoint *ep = xb->ep;
+	struct xillyusb_dev *xdev = ep->xdev;
+	int dws = xb->len >> 2;
+	__le32 *p = xb->buf;
+	u32 ctrlword;
+	struct xillyusb_channel *chan;
+	struct xillyfifo *fifo;
+	int chan_num = 0, opcode;
+	int chan_idx;
+	int bytes, count, dwconsume;
+	int in_bytes_left = 0;
+	int rc;
+
+	if ((dws << 2) != xb->len) {
+		pr_err("%s: Received BULK IN transfer with %d bytes, not a multiple of 4\n",
+		       err_name, xb->len);
+		return -EIO;
+	}
+
+	if (xdev->in_bytes_left) {
+		bytes = min(xdev->in_bytes_left, dws << 2);
+		in_bytes_left = xdev->in_bytes_left - bytes;
+		chan_num = xdev->leftover_chan_num;
+		goto resume_leftovers;
+	}
+
+	while (dws) {
+		ctrlword = le32_to_cpu(*p++);
+		dws--;
+
+		chan_num = ctrlword & 0xfff;
+		count = (ctrlword >> 12) & 0x3ff;
+		opcode = (ctrlword >> 24) & 0xf;
+
+		if (opcode != OPCODE_DATA) {
+			unsigned int in_counter = xdev->in_counter++ & 0x3ff;
+
+			if (count != in_counter) {
+				pr_err("%s: Expected opcode counter %d, got %d\n",
+				       err_name, in_counter, count);
+				return -EIO;
+			}
+
+			rc = process_in_opcode(xdev, opcode, chan_num);
+
+			if (rc)
+				return rc;
+
+			continue;
+		}
+
+		bytes = min(count + 1, dws << 2);
+		in_bytes_left = count + 1 - bytes;
+
+resume_leftovers:
+		chan_idx = chan_num >> 1;
+
+		if (!(chan_num & 1) || chan_idx >= xdev->num_channels ||
+		    !READ_ONCE(xdev->channels[chan_idx].read_data_ok)) {
+			pr_err("%s: Received illegal channel ID %d from FPGA\n",
+			       err_name, chan_num);
+			return -EIO;
+		}
+		chan = &xdev->channels[chan_idx];
+
+		fifo = chan->in_fifo;
+
+		if (unlikely(!fifo))
+			return -EIO; /* We got really unexpected data */
+
+		if (bytes != fifo_write(fifo, p, bytes, xilly_memcpy)) {
+			pr_err("%s: Misbehaving FPGA overflew an upstream FIFO!\n",
+			       err_name);
+			return -EIO;
+		}
+
+		wake_up_interruptible(&fifo->waitq);
+
+		dwconsume = (bytes + 3) >> 2;
+		dws -= dwconsume;
+		p += dwconsume;
+	}
+
+	xdev->in_bytes_left = in_bytes_left;
+	xdev->leftover_chan_num = chan_num;
+	return 0;
+}
+
+static void bulk_in_work(struct work_struct *work)
+{
+	struct xillyusb_endpoint *ep =
+		container_of(work, struct xillyusb_endpoint, workitem);
+	struct xillyusb_dev *xdev = ep->xdev;
+	unsigned long flags;
+	struct xillybuffer *xb;
+	bool consumed = false;
+	int rc = 0;
+
+	mutex_lock(&xdev->process_in_mutex);
+
+	spin_lock_irqsave(&ep->buffers_lock, flags);
+
+	while (1) {
+		if (list_empty(&ep->filled_buffers)) {
+			spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+			mutex_unlock(&xdev->process_in_mutex);
+
+			if (consumed)
+				try_queue_bulk_in(ep);
+
+			return;
+		}
+
+		xb = list_first_entry(&ep->filled_buffers, struct xillybuffer,
+				      entry);
+		list_del(&xb->entry);
+
+		spin_unlock_irqrestore(&ep->buffers_lock, flags);
+
+		consumed = true;
+
+		if (!xdev->error)
+			rc = process_bulk_in(xb);
+
+		if (rc) {
+			mutex_unlock(&xdev->process_in_mutex);
+			report_io_error(xdev, rc);
+			return;
+		}
+
+		spin_lock_irqsave(&ep->buffers_lock, flags);
+		list_add_tail(&xb->entry, &ep->buffers);
+		ep->outstanding_urbs--;
+	}
+}
+
+static int xillyusb_send_opcode(struct xillyusb_dev *xdev,
+				int chan_num, char opcode, u32 data)
+{
+	struct xillyusb_endpoint *ep = xdev->msg_ep;
+	struct xillyfifo *fifo = &ep->fifo;
+	__le32 msg[2];
+
+	int rc = 0;
+
+	msg[0] = cpu_to_le32((chan_num & 0xfff) |
+			     ((opcode & 0xf) << 24));
+	msg[1] = cpu_to_le32(data);
+
+	mutex_lock(&xdev->msg_mutex);
+
+	/*
+	 * The wait queue is woken with the interruptible variant, so the
+	 * wait function matches, however returning because of an interrupt
+	 * will mess things up considerably, in particular when the caller is
+	 * the release method. And the xdev->error part prevents being stuck
+	 * forever: Just pull the USB plug.
+	 */
+
+	while (wait_event_interruptible(fifo->waitq,
+					((atomic_read(&fifo->fill)
+					  <= (fifo->size - 8)) ||
+					 xdev->error)))
+		; /* Empty loop */
+
+	if (xdev->error) {
+		rc = xdev->error;
+		goto unlock_done;
+	}
+
+	fifo_write(fifo, (void *)msg, 8, xilly_memcpy);
+
+	try_queue_bulk_out(ep);
+
+unlock_done:
+	mutex_unlock(&xdev->msg_mutex);
+
+	return rc;
+}
+
+/*
+ * Note that flush_downstream() merely waits for the data to arrive to
+ * the application logic at the FPGA -- unlike PCIe Xillybus' counterpart,
+ * it does nothing to make it happen (and neither is it necessary).
+ *
+ * This function is not reentrant for the same @chan, but this is covered
+ * by the fact that for any given @chan, it's called either by the open,
+ * write, llseek and flush fops methods, which can't run in parallel (and the
+ * write + flush and llseek method handlers are protected with out_mutex).
+ *
+ * chan->flushed is there to avoid multiple flushes at the same position,
+ * in particular as a result of programs that close the file descriptor
+ * e.g. after a dup2() for redirection.
+ */
+
+static int flush_downstream(struct xillyusb_channel *chan,
+			    long timeout,
+			    bool interruptible)
+{
+	struct xillyusb_dev *xdev = chan->xdev;
+	int chan_num = chan->chan_idx << 1;
+	long deadline, left_to_sleep;
+	int rc;
+
+	if (chan->flushed)
+		return 0;
+
+	deadline = jiffies + 1 + timeout;
+
+	if (chan->flushing) {
+		long cancel_deadline = jiffies + 1 + XILLY_RESPONSE_TIMEOUT;
+
+		chan->canceled = 0;
+		rc = xillyusb_send_opcode(xdev, chan_num,
+					  OPCODE_CANCEL_CHECKPOINT, 0);
+
+		if (rc)
+			return rc; /* Only real error, never -EINTR */
+
+		/* Ignoring interrupts. Cancellation must be handled */
+		while (!chan->canceled) {
+			left_to_sleep = cancel_deadline - ((long)jiffies);
+
+			if (left_to_sleep <= 0) {
+				report_io_error(xdev, -EIO);
+				pr_err("%s: Fatal error: Timed out on flush cancellation request.\n",
+				       err_name);
+				return -EIO;
+			}
+
+			rc = wait_event_interruptible_timeout(chan->flushq,
+							      chan->canceled ||
+							      xdev->error,
+							      left_to_sleep);
+
+			if (xdev->error)
+				return xdev->error;
+		}
+	}
+
+	chan->flushing = 1;
+
+	/*
+	 * The checkpoint is given in terms of data elements, not bytes. As
+	 * a result, if less than an element's worth of data is stored in the
+	 * FIFO, it's not flushed, including the flush before closing, which
+	 * means that such data is lost. This is consistent with PCIe Xillybus.
+	 */
+
+	rc = xillyusb_send_opcode(xdev, chan_num,
+				  OPCODE_SET_CHECKPOINT,
+				  chan->out_bytes >>
+				  chan->out_log2_element_size);
+
+	if (rc)
+		return rc; /* Only real error, never -EINTR */
+
+	if (!timeout) {
+		while (chan->flushing) {
+			rc = wait_event_interruptible(chan->flushq,
+						      !chan->flushing ||
+						      xdev->error);
+			if (xdev->error)
+				return xdev->error;
+
+			if (interruptible && rc)
+				return -EINTR;
+		}
+
+		goto done;
+	}
+
+	while (chan->flushing) {
+		left_to_sleep = deadline - ((long)jiffies);
+
+		if (left_to_sleep <= 0)
+			return -ETIMEDOUT;
+
+		rc = wait_event_interruptible_timeout(chan->flushq,
+						      !chan->flushing ||
+						      xdev->error,
+						      left_to_sleep);
+
+		if (xdev->error)
+			return xdev->error;
+
+		if (interruptible && rc < 0)
+			return -EINTR;
+	}
+
+done:
+	chan->flushed = 1;
+	return 0;
+}
+
+/* request_read_anything(): Ask the FPGA for any little amount of data */
+static int request_read_anything(struct xillyusb_channel *chan,
+				 char opcode)
+{
+	struct xillyusb_dev *xdev = chan->xdev;
+	unsigned int sh = chan->in_log2_element_size;
+	int chan_num = (chan->chan_idx << 1) | 1;
+	u32 mercy = chan->in_consumed_bytes + (2 << sh) - 1;
+
+	return xillyusb_send_opcode(xdev, chan_num, opcode, mercy >> sh);
+}
+
+static int xillyusb_open(struct inode *inode, struct file *filp)
+{
+	int minor = iminor(inode);
+	int major = imajor(inode);
+	struct xillyusb_dev *xdev_iter, *xdev = NULL;
+	struct xillyusb_channel *chan;
+	struct xillyfifo *in_fifo = NULL;
+	struct xillyusb_endpoint *out_ep = NULL;
+
+	int rc = -ENODEV;
+
+	mutex_lock(&xdev_mutex);
+
+	list_for_each_entry(xdev_iter, &xdev_list, list_entry) {
+		if (xdev_iter->major == major &&
+		    minor >= xdev_iter->lowest_minor &&
+		    minor < (xdev_iter->lowest_minor +
+			     xdev_iter->num_channels)) {
+			xdev = xdev_iter;
+			break;
+		}
+	}
+
+	if (!xdev)
+		goto unmutex_fail;
+
+	chan = &xdev->channels[minor - xdev->lowest_minor];
+	filp->private_data = chan;
+
+	if (((filp->f_mode & FMODE_READ) && !chan->readable) ||
+	    ((filp->f_mode & FMODE_WRITE) && !chan->writable))
+		goto unmutex_fail;
+
+	if ((filp->f_flags & O_NONBLOCK) && (filp->f_mode & FMODE_READ) &&
+	    chan->in_synchronous) {
+		pr_err("%s: open() failed: O_NONBLOCK not allowed for read on this device\n",
+		       err_name);
+		goto unmutex_fail;
+	}
+
+	if ((filp->f_flags & O_NONBLOCK) && (filp->f_mode & FMODE_WRITE) &&
+	    chan->out_synchronous) {
+		pr_err("%s: open() failed: O_NONBLOCK not allowed for write on this device\n",
+		       err_name);
+		goto unmutex_fail;
+	}
+
+	rc = -EBUSY;
+
+	if (((filp->f_mode & FMODE_READ) && chan->open_for_read) ||
+	    ((filp->f_mode & FMODE_WRITE) && chan->open_for_write))
+		goto unmutex_fail;
+
+	kref_get(&xdev->kref);
+
+	if (filp->f_mode & FMODE_READ)
+		chan->open_for_read = 1;
+
+	if (filp->f_mode & FMODE_WRITE)
+		chan->open_for_write = 1;
+
+	mutex_unlock(&xdev_mutex);
+
+	if (filp->f_mode & FMODE_WRITE) {
+		out_ep = endpoint_alloc(xdev,
+					(chan->chan_idx + 2) | USB_DIR_OUT,
+					bulk_out_work, BUF_SIZE_ORDER, BUFNUM);
+
+		if (!out_ep) {
+			rc = -ENOMEM;
+			goto unopen;
+		}
+
+		rc = fifo_init(&out_ep->fifo, chan->out_log2_fifo_size);
+
+		if (rc)
+			goto late_unopen;
+
+		out_ep->fill_mask = -(1 << chan->out_log2_element_size);
+		chan->out_bytes = 0;
+		chan->flushed = 0;
+
+		/*
+		 * Sending a flush request to a previously closed stream
+		 * effectively opens it, and also waits until the command is
+		 * confirmed by the FPGA. The latter is necessary because the
+		 * data is sent through a separate BULK OUT endpoint, and the
+		 * xHCI controller is free to reorder transmissions.
+		 *
+		 * This can't go wrong unless there's a serious hardware error
+		 * (or the computer is stuck for 500 ms?)
+		 */
+		rc = flush_downstream(chan, XILLY_RESPONSE_TIMEOUT, false);
+
+		if (rc == -ETIMEDOUT) {
+			rc = -EIO;
+			report_io_error(xdev, rc);
+			pr_err("%s: Fatal error: Hardware timed out to open request.\n",
+			       err_name);
+		}
+
+		if (rc)
+			goto late_unopen;
+	}
+
+	if (filp->f_mode & FMODE_READ) {
+		in_fifo = kzalloc(sizeof(*in_fifo), GFP_KERNEL);
+
+		if (!in_fifo) {
+			rc = -ENOMEM;
+			goto late_unopen;
+		}
+
+		rc = fifo_init(in_fifo, chan->in_log2_fifo_size);
+
+		if (rc) {
+			kfree(in_fifo);
+			goto late_unopen;
+		}
+	}
+
+	mutex_lock(&chan->lock);
+	if (in_fifo) {
+		chan->in_fifo = in_fifo;
+		chan->read_data_ok = 1;
+	}
+	if (out_ep)
+		chan->out_ep = out_ep;
+	mutex_unlock(&chan->lock);
+
+	if (in_fifo) {
+		u32 in_checkpoint = 0;
+
+		if (!chan->in_synchronous)
+			in_checkpoint = in_fifo->size >>
+				chan->in_log2_element_size;
+
+		chan->in_consumed_bytes = 0;
+		chan->poll_used = 0;
+		chan->in_current_checkpoint = in_checkpoint;
+		rc = xillyusb_send_opcode(xdev, (chan->chan_idx << 1) | 1,
+					  OPCODE_SET_CHECKPOINT,
+					  in_checkpoint);
+
+		if (rc) /* Failure guarantees that opcode wasn't sent */
+			goto unfifo;
+
+		/*
+		 * In non-blocking mode, request the FPGA to send any data it
+		 * has right away. Otherwise, the first read() will always
+		 * return -EAGAIN, which is OK strictly speaking, but ugly.
+		 * Checking and unrolling if this fails isn't worth the
+		 * effort -- the error is propagated to the first read()
+		 * anyhow.
+		 */
+		if (filp->f_flags & O_NONBLOCK)
+			request_read_anything(chan, OPCODE_SET_PUSH);
+	}
+
+	return 0;
+
+unfifo:
+	if (in_fifo) {
+		chan->read_data_ok = 0;
+		safely_assign_in_fifo(chan, NULL);
+		fifo_mem_release(in_fifo);
+	}
+
+	if (out_ep) {
+		mutex_lock(&chan->lock);
+		chan->out_ep = NULL;
+		mutex_unlock(&chan->lock);
+	}
+
+late_unopen:
+	if (out_ep)
+		endpoint_dealloc(out_ep);
+
+unopen:
+	mutex_lock(&xdev_mutex);
+
+	if (filp->f_mode & FMODE_READ)
+		chan->open_for_read = 0;
+
+	if (filp->f_mode & FMODE_WRITE)
+		chan->open_for_write = 0;
+
+	mutex_unlock(&xdev_mutex);
+
+	kref_put(&xdev->kref, cleanup_dev);
+
+	return rc;
+
+unmutex_fail:
+	mutex_unlock(&xdev_mutex);
+	return rc;
+}
+
+static int xilly_copy_to_user(void *dst, const void *src, int n)
+{
+	return copy_to_user((void __user *)dst, src, n);
+}
+
+static ssize_t xillyusb_read(struct file *filp, char __user *userbuf,
+			     size_t count, loff_t *f_pos)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	struct xillyusb_dev *xdev = chan->xdev;
+	struct xillyfifo *fifo = chan->in_fifo;
+	int chan_num = (chan->chan_idx << 1) | 1;
+
+	long deadline, left_to_sleep;
+	int bytes_done = 0;
+	bool sent_set_push = false;
+	int rc;
+
+	deadline = jiffies + 1 + XILLY_RX_TIMEOUT;
+
+	rc = mutex_lock_interruptible(&chan->in_mutex);
+
+	if (rc)
+		return rc;
+
+	while (1) {
+		u32 fifo_checkpoint_bytes, complete_checkpoint_bytes;
+		u32 complete_checkpoint, fifo_checkpoint;
+		u32 checkpoint;
+		s32 diff, leap;
+		unsigned int sh = chan->in_log2_element_size;
+		bool checkpoint_for_complete;
+
+		rc = fifo_read(fifo, (__force void *)userbuf + bytes_done,
+			       count - bytes_done, xilly_copy_to_user);
+
+		if (rc < 0)
+			break;
+
+		bytes_done += rc;
+		chan->in_consumed_bytes += rc;
+
+		left_to_sleep = deadline - ((long)jiffies);
+
+		/*
+		 * Some 32-bit arithmetics that may wrap. Note that
+		 * complete_checkpoint is rounded up to the closest element
+		 * boundary, because the read() can't be completed otherwise.
+		 * fifo_checkpoint_bytes is rounded down, because it protects
+		 * in_fifo from overflowing.
+		 */
+
+		fifo_checkpoint_bytes = chan->in_consumed_bytes + fifo->size;
+		complete_checkpoint_bytes =
+			chan->in_consumed_bytes + count - bytes_done;
+
+		fifo_checkpoint = fifo_checkpoint_bytes >> sh;
+		complete_checkpoint =
+			(complete_checkpoint_bytes + (1 << sh) - 1) >> sh;
+
+		diff = (fifo_checkpoint - complete_checkpoint) << sh;
+
+		if (chan->in_synchronous && diff >= 0) {
+			checkpoint = complete_checkpoint;
+			checkpoint_for_complete = true;
+		} else {
+			checkpoint = fifo_checkpoint;
+			checkpoint_for_complete = false;
+		}
+
+		leap = (checkpoint - chan->in_current_checkpoint) << sh;
+
+		/*
+		 * To prevent flooding of OPCODE_SET_CHECKPOINT commands as
+		 * data is consumed, it's issued only if it moves the
+		 * checkpoint by at least an 8th of the FIFO's size, or if
+		 * it's necessary to complete the number of bytes requested by
+		 * the read() call.
+		 *
+		 * chan->read_data_ok is checked to spare an unnecessary
+		 * submission after receiving EOF, however it's harmless if
+		 * such slips away.
+		 */
+
+		if (chan->read_data_ok &&
+		    (leap > (fifo->size >> 3) ||
+		     (checkpoint_for_complete && leap > 0))) {
+			chan->in_current_checkpoint = checkpoint;
+			rc = xillyusb_send_opcode(xdev, chan_num,
+						  OPCODE_SET_CHECKPOINT,
+						  checkpoint);
+
+			if (rc)
+				break;
+		}
+
+		if (bytes_done == count ||
+		    (left_to_sleep <= 0 && bytes_done))
+			break;
+
+		/*
+		 * Reaching here means that the FIFO was empty at the call to
+		 * fifo_read() above, but not necessarily right now. Error
+		 * and EOF are checked and reported only now, so that no data
+		 * that managed its way to the FIFO is lost.
+		 */
+
+		if (!READ_ONCE(chan->read_data_ok)) { /* FPGA has sent EOF */
+			/* Has data slipped into the FIFO since fifo_read()? */
+			smp_rmb();
+			if (atomic_read(&fifo->fill))
+				continue;
+
+			rc = 0;
+			break;
+		}
+
+		if (xdev->error) {
+			rc = xdev->error;
+			break;
+		}
+
+		if (filp->f_flags & O_NONBLOCK) {
+			rc = -EAGAIN;
+			break;
+		}
+
+		if (left_to_sleep > 0) {
+			if (!sent_set_push) {
+				rc = xillyusb_send_opcode(xdev, chan_num,
+							  OPCODE_SET_PUSH,
+							  complete_checkpoint);
+
+				if (rc)
+					break;
+
+				sent_set_push = true;
+			}
+
+			/*
+			 * Note that when xdev->error is set (e.g. when the
+			 * device is unplugged), read_data_ok turns zero and
+			 * fifo->waitq is awaken.
+			 * Therefore no special attention to xdev->error.
+			 */
+
+			rc = wait_event_interruptible_timeout
+				(fifo->waitq,
+				 atomic_read(&fifo->fill) ||
+				 !chan->read_data_ok,
+				 left_to_sleep);
+		} else { /* bytes_done == 0 */
+			/* Tell FPGA to send anything it has */
+			rc = request_read_anything(chan, OPCODE_UPDATE_PUSH);
+
+			if (rc)
+				break;
+
+			rc = wait_event_interruptible
+				(fifo->waitq,
+				 atomic_read(&fifo->fill) ||
+				 !chan->read_data_ok);
+		}
+
+		if (rc < 0) {
+			rc = -EINTR;
+			break;
+		}
+	}
+
+	if (((filp->f_flags & O_NONBLOCK) || chan->poll_used) &&
+	    !atomic_read(&fifo->fill))
+		request_read_anything(chan, OPCODE_SET_PUSH);
+
+	mutex_unlock(&chan->in_mutex);
+
+	if (bytes_done)
+		return bytes_done;
+
+	return rc;
+}
+
+static int xillyusb_flush(struct file *filp, fl_owner_t id)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	int rc;
+
+	if (!(filp->f_mode & FMODE_WRITE))
+		return 0;
+
+	rc = mutex_lock_interruptible(&chan->out_mutex);
+
+	if (rc)
+		return rc;
+
+	/*
+	 * One second's timeout on flushing. Interrupts are ignored, because if
+	 * the user pressed CTRL-C, that interrupt will still be in flight by
+	 * the time we reach here, and the opportunity to flush is lost.
+	 */
+	rc = flush_downstream(chan, HZ, false);
+
+	if (rc == -ETIMEDOUT)
+		pr_warn("%s: Timed out while flushing. Output data may be lost.\n",
+			err_name);
+
+	mutex_unlock(&chan->out_mutex);
+
+	return rc;
+}
+
+static int xilly_copy_from_user(void *dst, const void *src, int n)
+{
+	return copy_from_user(dst, (const void __user *)src, n);
+}
+
+static ssize_t xillyusb_write(struct file *filp, const char __user *userbuf,
+			      size_t count, loff_t *f_pos)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	struct xillyusb_dev *xdev = chan->xdev;
+	struct xillyfifo *fifo = &chan->out_ep->fifo;
+	int rc;
+
+	rc = mutex_lock_interruptible(&chan->out_mutex);
+
+	if (rc)
+		return rc;
+
+	while (1) {
+		if (xdev->error) {
+			rc = xdev->error;
+			break;
+		}
+
+		if (count == 0)
+			break;
+
+		rc = fifo_write(fifo, (__force void *)userbuf, count,
+				xilly_copy_from_user);
+
+		if (rc != 0)
+			break;
+
+		if (filp->f_flags & O_NONBLOCK) {
+			rc = -EAGAIN;
+			break;
+		}
+
+		if (wait_event_interruptible
+		    (fifo->waitq,
+		     (atomic_read(&fifo->fill) != fifo->size) ||
+		     xdev->error)) {
+			rc = -EINTR;
+			break;
+		}
+	}
+
+	if (rc < 0)
+		goto done;
+
+	chan->out_bytes += rc;
+
+	if (rc) {
+		try_queue_bulk_out(chan->out_ep);
+		chan->flushed = 0;
+	}
+
+	if (chan->out_synchronous) {
+		int flush_rc = flush_downstream(chan, 0, true);
+
+		if (flush_rc && !rc)
+			rc = flush_rc;
+	}
+
+done:
+	mutex_unlock(&chan->out_mutex);
+
+	return rc;
+}
+
+static int xillyusb_release(struct inode *inode, struct file *filp)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	struct xillyusb_dev *xdev = chan->xdev;
+	int rc_read = 0, rc_write = 0;
+
+	if (filp->f_mode & FMODE_READ) {
+		struct xillyfifo *in_fifo = chan->in_fifo;
+
+		rc_read = xillyusb_send_opcode(xdev, (chan->chan_idx << 1) | 1,
+					       OPCODE_CLOSE, 0);
+		/*
+		 * If rc_read is nonzero, xdev->error indicates a global
+		 * device error. The error is reported later, so that
+		 * resources are freed.
+		 *
+		 * Looping on wait_event_interruptible() kinda breaks the idea
+		 * of being interruptible, and this should have been
+		 * wait_event(). Only it's being waken with
+		 * wake_up_interruptible() for the sake of other uses. If
+		 * there's a global device error, chan->read_data_ok is
+		 * deasserted and the wait queue is awaken, so this is covered.
+		 */
+
+		while (wait_event_interruptible(in_fifo->waitq,
+						!chan->read_data_ok))
+			; /* Empty loop */
+
+		safely_assign_in_fifo(chan, NULL);
+		fifo_mem_release(in_fifo);
+
+		mutex_lock(&xdev_mutex);
+		chan->open_for_read = 0;
+		mutex_unlock(&xdev_mutex);
+	}
+
+	if (filp->f_mode & FMODE_WRITE) {
+		struct xillyusb_endpoint *ep = chan->out_ep;
+		/*
+		 * chan->flushing isn't zeroed. If the pre-release flush timed
+		 * out, a cancel request will be sent before the next
+		 * OPCODE_SET_CHECKPOINT (i.e. when the file is opened again).
+		 * This is despite that the FPGA forgets about the checkpoint
+		 * request as the file closes. Still, in an exceptional race
+		 * condition, the FPGA could send an OPCODE_REACHED_CHECKPOINT
+		 * just before closing that would reach the host after the
+		 * file has re-opened.
+		 */
+
+		mutex_lock(&chan->lock);
+		chan->out_ep = NULL;
+		mutex_unlock(&chan->lock);
+
+		endpoint_dealloc(ep);
+
+		/* See comments on rc_read above */
+		rc_write = xillyusb_send_opcode(xdev, chan->chan_idx << 1,
+						OPCODE_CLOSE, 0);
+
+		mutex_lock(&xdev_mutex);
+		chan->open_for_write = 0;
+		mutex_unlock(&xdev_mutex);
+	}
+
+	kref_put(&xdev->kref, cleanup_dev);
+
+	return rc_read ? rc_read : rc_write;
+}
+
+static loff_t xillyusb_llseek(struct file *filp, loff_t offset, int whence)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	struct xillyusb_dev *xdev = chan->xdev;
+	loff_t pos = filp->f_pos;
+	int rc = 0;
+	unsigned int log2_element_size = chan->readable ?
+		chan->in_log2_element_size : chan->out_log2_element_size;
+
+	/*
+	 * Take both mutexes not allowing interrupts, since it seems like
+	 * common applications don't expect an -EINTR here. Besides, multiple
+	 * access to a single file descriptor on seekable devices is a mess
+	 * anyhow.
+	 */
+
+	mutex_lock(&chan->out_mutex);
+	mutex_lock(&chan->in_mutex);
+
+	switch (whence) {
+	case 0:
+		pos = offset;
+		break;
+	case 1:
+		pos += offset;
+		break;
+	case 2:
+		pos = offset; /* Going to the end => to the beginning */
+		break;
+	default:
+		rc = -EINVAL;
+		goto end;
+	}
+
+	/* In any case, we must finish on an element boundary */
+	if (pos & ((1 << log2_element_size) - 1)) {
+		rc = -EINVAL;
+		goto end;
+	}
+
+	rc = xillyusb_send_opcode(xdev, chan->chan_idx << 1,
+				  OPCODE_SET_ADDR,
+				  pos >> log2_element_size);
+
+	if (rc)
+		goto end;
+
+	/*
+	 * If the stream is writable (it most likely is), a flush request is
+	 * sent to ensure that traffic on the stream's BULK OUT endpoint isn't
+	 * sent before the position is updated on the FPGA -- otherwise that
+	 * data could arrive before the position update. Since only
+	 * synchronous streams can be seekable, flush_downstream() has already
+	 * been called after the last write(), so flushing is completed
+	 * virtually right away. Well, unless the last flush was interrupted,
+	 * in which case we wait for up to 1000 ms, and return -ETIMEDOUT (!)
+	 * if the flush was incomplete. No real-life application should ever
+	 * get to this point.
+	 */
+
+	if (chan->writable) {
+		chan->flushed = 0;
+		rc = flush_downstream(chan, HZ, false);
+	}
+
+end:
+	mutex_unlock(&chan->out_mutex);
+	mutex_unlock(&chan->in_mutex);
+
+	if (rc) /* Return error after releasing mutexes */
+		return rc;
+
+	filp->f_pos = pos;
+
+	return pos;
+}
+
+static __poll_t xillyusb_poll(struct file *filp, poll_table *wait)
+{
+	struct xillyusb_channel *chan = filp->private_data;
+	__poll_t mask = 0;
+
+	if (chan->in_fifo)
+		poll_wait(filp, &chan->in_fifo->waitq, wait);
+
+	if (chan->out_ep)
+		poll_wait(filp, &chan->out_ep->fifo.waitq, wait);
+
+	/*
+	 * If this is the first time poll() is called, and the file is
+	 * readable, set the relevant flag. Also tell the FPGA to send all it
+	 * has, to kickstart the mechanism that ensures there's always some
+	 * data in in_fifo unless the stream is dry end-to-end. Note that the
+	 * first poll() may not return a EPOLLIN, even if there's data on the
+	 * FPGA. Rather, the data will arrive soon, and trigger the relevant
+	 * wait queue.
+	 */
+
+	if (!chan->poll_used && chan->in_fifo) {
+		chan->poll_used = 1;
+		request_read_anything(chan, OPCODE_SET_PUSH);
+	}
+
+	/*
+	 * poll() won't play ball regarding read() channels which
+	 * are synchronous. Allowing that will create situations where data has
+	 * been delivered at the FPGA, and users expecting select() to wake up,
+	 * which it may not. So make it never work.
+	 */
+
+	if (chan->in_fifo && !chan->in_synchronous &&
+	    (atomic_read(&chan->in_fifo->fill) || !chan->read_data_ok))
+		mask |= EPOLLIN | EPOLLRDNORM;
+
+	if (chan->out_ep &&
+	    (atomic_read(&chan->out_ep->fifo.fill) !=
+	     chan->out_ep->fifo.size))
+		mask |= EPOLLOUT | EPOLLWRNORM;
+
+	if (chan->xdev->error)
+		mask |= EPOLLERR;
+
+	return mask;
+}
+
+static const struct file_operations xillyusb_fops = {
+	.owner      = THIS_MODULE,
+	.read       = xillyusb_read,
+	.write      = xillyusb_write,
+	.open       = xillyusb_open,
+	.flush      = xillyusb_flush,
+	.release    = xillyusb_release,
+	.llseek     = xillyusb_llseek,
+	.poll       = xillyusb_poll,
+};
+
+/*
+ * Called from xillyusb_probe() only, hence interface->dev is guaranteed to
+ * be valid.
+ */
+
+static int xillyusb_init_chrdev(struct usb_interface *interface,
+				unsigned char *names,
+				unsigned int len)
+{
+	int rc;
+	dev_t dev;
+	int i;
+	char devname[48];
+	struct device *device;
+	size_t namelen;
+
+	struct xillyusb_dev *xdev = usb_get_intfdata(interface);
+
+	rc = alloc_chrdev_region(&dev, 0, /* minor start */
+				 xdev->num_channels,
+				 xillyname);
+	if (rc) {
+		dev_warn(&interface->dev, "Failed to obtain major/minors");
+		return rc;
+	}
+
+	/* With cdev_alloc(), the allocated memory is freed automatically */
+	xdev->cdev = cdev_alloc();
+	if (!xdev->cdev)
+		goto unregister_chrdev;
+
+	xdev->cdev->ops = &xillyusb_fops;
+	xdev->cdev->owner = THIS_MODULE;
+
+	xdev->major = MAJOR(dev);
+	xdev->lowest_minor = MINOR(dev);
+
+	rc = cdev_add(xdev->cdev, MKDEV(xdev->major, xdev->lowest_minor),
+		      xdev->num_channels);
+	if (rc) {
+		dev_warn(&interface->dev, "Failed to add cdev. Aborting.\n");
+		/* kobject_put() is normally done by cdev_del() */
+		kobject_put(&xdev->cdev->kobj);
+		goto unregister_chrdev;
+	}
+
+	for (i = 0; i < xdev->num_channels; i++) {
+		namelen = strnlen(names, len);
+
+		if (namelen == len) {
+			dev_err(&interface->dev, "IDT's list of names is too short. This is exceptionally weird, because its CRC is OK\n");
+			rc = -ENODEV;
+			goto unroll_device_create;
+		}
+
+		snprintf(devname, sizeof(devname) - 1, "xillyusb_%02d_%s",
+			 xdev->index, names);
+
+		devname[sizeof(devname) - 1] = 0; /* Should never matter */
+
+		len -= namelen + 1;
+		names += namelen + 1;
+
+		device = device_create(xillyusb_class,
+				       NULL,
+				       MKDEV(xdev->major,
+					     i + xdev->lowest_minor),
+				       NULL,
+				       "%s", devname);
+
+		if (IS_ERR(device)) {
+			dev_err(&interface->dev,
+				"Failed to create %s device. Aborting.\n",
+				devname);
+			rc = -ENODEV;
+			goto unroll_device_create;
+		}
+	}
+
+	dev_info(&interface->dev, "Created %d device files.\n",
+		 xdev->num_channels);
+	return 0; /* succeed */
+
+unroll_device_create:
+	for (i--; i >= 0; i--)
+		device_destroy(xillyusb_class, MKDEV(xdev->major,
+						     i + xdev->lowest_minor));
+
+	cdev_del(xdev->cdev);
+unregister_chrdev:
+	unregister_chrdev_region(MKDEV(xdev->major, xdev->lowest_minor),
+				 xdev->num_channels);
+
+	return rc;
+}
+
+/*
+ * Called from xillyusb_disconnect() only, hence interface->dev is
+ * guaranteed to be valid.
+ */
+
+static void xillyusb_cleanup_chrdev(struct usb_interface *interface)
+{
+	int minor;
+	struct xillyusb_dev *xdev = usb_get_intfdata(interface);
+
+	for (minor = xdev->lowest_minor;
+	     minor < (xdev->lowest_minor + xdev->num_channels);
+	     minor++)
+		device_destroy(xillyusb_class, MKDEV(xdev->major, minor));
+	cdev_del(xdev->cdev);
+	unregister_chrdev_region(MKDEV(xdev->major,
+				       xdev->lowest_minor),
+				 xdev->num_channels);
+
+	dev_info(&interface->dev, "Removed %d device files.\n",
+		 xdev->num_channels);
+}
+
+static int xillyusb_setup_base_eps(struct xillyusb_dev *xdev)
+{
+	xdev->msg_ep = endpoint_alloc(xdev, MSG_EP_NUM | USB_DIR_OUT,
+				      bulk_out_work, 1, 2);
+	if (!xdev->msg_ep)
+		return -ENOMEM;
+
+	if (fifo_init(&xdev->msg_ep->fifo, 13)) /* 8 kiB */
+		goto dealloc;
+
+	xdev->msg_ep->fill_mask = -8; /* 8 bytes granularity */
+
+	xdev->in_ep = endpoint_alloc(xdev, IN_EP_NUM | USB_DIR_IN,
+				     bulk_in_work, BUF_SIZE_ORDER, BUFNUM);
+	if (!xdev->in_ep)
+		goto dealloc;
+
+	try_queue_bulk_in(xdev->in_ep);
+
+	return 0;
+
+dealloc:
+	endpoint_dealloc(xdev->msg_ep); /* Also frees FIFO mem if allocated */
+	return -ENOMEM;
+}
+
+static int setup_channels(struct xillyusb_dev *xdev,
+			  __le16 *chandesc)
+{
+	struct xillyusb_channel *chan;
+	int i;
+
+	chan = kcalloc(xdev->num_channels, sizeof(*chan), GFP_KERNEL);
+	if (!chan)
+		return -ENOMEM;
+
+	xdev->channels = chan;
+
+	for (i = 0; i < xdev->num_channels; i++, chan++) {
+		unsigned int in_desc = le16_to_cpu(*chandesc++);
+		unsigned int out_desc = le16_to_cpu(*chandesc++);
+
+		chan->xdev = xdev;
+		mutex_init(&chan->in_mutex);
+		mutex_init(&chan->out_mutex);
+		mutex_init(&chan->lock);
+		init_waitqueue_head(&chan->flushq);
+
+		chan->chan_idx = i;
+
+		if (in_desc & 0x80) { /* Entry is valid */
+			chan->readable = 1;
+			chan->in_synchronous = !!(in_desc & 0x40);
+			chan->in_seekable = !!(in_desc & 0x20);
+			chan->in_log2_element_size = in_desc & 0x0f;
+			chan->in_log2_fifo_size = ((in_desc >> 8) & 0x1f) + 16;
+		}
+
+		if (out_desc & 0x80) { /* Entry is valid */
+			chan->writable = 1;
+			chan->out_synchronous = !!(out_desc & 0x40);
+			chan->out_seekable = !!(out_desc & 0x20);
+			chan->out_log2_element_size = out_desc & 0x0f;
+			chan->out_log2_fifo_size =
+				((out_desc >> 8) & 0x1f) + 16;
+		}
+	}
+
+	return 0;
+}
+
+static int xillyusb_discovery(struct usb_interface *interface)
+{
+	int rc;
+	struct xillyusb_dev *xdev = usb_get_intfdata(interface);
+	__le16 bogus_chandesc[2];
+	struct xillyfifo idt_fifo;
+	struct xillyusb_channel *chan;
+	unsigned int idt_len, names_offset;
+	unsigned char *idt;
+
+	rc = xillyusb_send_opcode(xdev, ~0, OPCODE_QUIESCE, 0);
+
+	if (rc) {
+		dev_err(&interface->dev, "Failed to send quiesce request. Aborting.\n");
+		return rc;
+	}
+
+	/* Phase I: Set up one fake upstream channel and obtain IDT */
+
+	/* Set up a fake IDT with one async IN stream */
+	xdev->num_channels = 1;
+	bogus_chandesc[0] = cpu_to_le16(0x80);
+	bogus_chandesc[1] = cpu_to_le16(0);
+
+	rc = setup_channels(xdev, bogus_chandesc);
+
+	if (rc)
+		return rc;
+
+	rc = fifo_init(&idt_fifo, LOG2_IDT_FIFO_SIZE);
+
+	if (rc)
+		return rc;
+
+	chan = xdev->channels;
+
+	chan->in_fifo = &idt_fifo;
+	chan->read_data_ok = 1;
+
+	rc = xillyusb_send_opcode(xdev, ~0, OPCODE_REQ_IDT, 0);
+
+	if (rc) {
+		dev_err(&interface->dev, "Failed to send IDT request. Aborting.\n");
+		goto unfifo;
+	}
+
+	rc = wait_event_interruptible_timeout(idt_fifo.waitq,
+					      !chan->read_data_ok,
+					      XILLY_RESPONSE_TIMEOUT);
+
+	if (xdev->error) {
+		rc = xdev->error;
+		goto unfifo;
+	}
+
+	if (rc < 0) {
+		rc = -EINTR; /* Interrupt on probe method? Interesting. */
+		goto unfifo;
+	}
+
+	if (chan->read_data_ok) {
+		rc = -ETIMEDOUT;
+		dev_err(&interface->dev, "No response from FPGA. Aborting.\n");
+		goto unfifo;
+	}
+
+	idt_len = atomic_read(&idt_fifo.fill);
+	idt = kmalloc(idt_len, GFP_KERNEL);
+
+	if (!idt)
+		goto unfifo;
+
+	fifo_read(&idt_fifo, idt, idt_len, xilly_memcpy);
+
+	if (crc32_le(~0, idt, idt_len) != 0) {
+		dev_err(&interface->dev, "IDT failed CRC check. Aborting.\n");
+		rc = -ENODEV;
+		goto unidt;
+	}
+
+	if (*idt > 0x90) {
+		dev_err(&interface->dev, "No support for IDT version 0x%02x. Maybe the xillyusb driver needs an upgarde. Aborting.\n",
+			(int)*idt);
+		rc = -ENODEV;
+		goto unidt;
+	}
+
+	/* Phase II: Set up the streams as defined in IDT */
+
+	xdev->num_channels = le16_to_cpu(*((__le16 *)(idt + 1)));
+	names_offset = 3 + xdev->num_channels * 4;
+	idt_len -= 4; /* Exclude CRC */
+
+	if (idt_len < names_offset) {
+		dev_err(&interface->dev, "IDT too short. This is exceptionally weird, because its CRC is OK\n");
+		rc = -ENODEV;
+		goto unidt;
+	}
+
+	rc = setup_channels(xdev, (void *)idt + 3);
+
+	if (rc)
+		goto unidt;
+
+	/*
+	 * Except for wildly misbehaving hardware, or if it was disconnected
+	 * just after responding with the IDT, there is no reason for any
+	 * work item to be running now. To be sure that xdev->channel
+	 * is updated on anything that might run in parallel, flush the
+	 * workqueue, which rarely does anything.
+	 */
+	flush_workqueue(xdev->workq);
+
+	fifo_mem_release(&idt_fifo);
+	kfree(chan);
+
+	rc = xillyusb_init_chrdev(interface, idt + names_offset,
+				  idt_len - names_offset);
+
+	kfree(idt);
+
+	return rc;
+
+unidt:
+	kfree(idt);
+
+unfifo:
+	safely_assign_in_fifo(chan, NULL);
+	fifo_mem_release(&idt_fifo);
+
+	return rc;
+}
+
+static int xillyusb_probe(struct usb_interface *interface,
+			  const struct usb_device_id *id)
+{
+	struct xillyusb_dev *xdev;
+	int rc;
+	int i;
+
+	xdev = kzalloc(sizeof(*xdev), GFP_KERNEL);
+	if (!xdev)
+		return -ENOMEM;
+
+	kref_init(&xdev->kref);
+	mutex_init(&xdev->io_mutex);
+	mutex_init(&xdev->process_in_mutex);
+	mutex_init(&xdev->msg_mutex);
+
+	xdev->udev = usb_get_dev(interface_to_usbdev(interface));
+	xdev->interface = interface;
+	xdev->error = 0;
+	spin_lock_init(&xdev->error_lock);
+	xdev->in_counter = 0;
+	xdev->in_bytes_left = 0;
+	xdev->workq = alloc_workqueue(xillyname, WQ_HIGHPRI, 0);
+
+	if (!xdev->workq) {
+		dev_err(&interface->dev, "Failed to allocate work queue\n");
+		rc = -ENOMEM;
+		goto fail;
+	}
+
+	INIT_WORK(&xdev->wakeup_workitem, wakeup_all);
+
+	usb_set_intfdata(interface, xdev);
+
+	mutex_lock(&xdev_mutex);
+
+	for (i = 0; i < MAX_XILLYUSB_DEVS; i++)
+		if (!xdev_map[i])
+			break;
+
+	if (i == MAX_XILLYUSB_DEVS) {
+		dev_err(&interface->dev,
+			"Reached limit of %d maximal devices. Aborting.\n",
+			MAX_XILLYUSB_DEVS);
+		mutex_unlock(&xdev_mutex);
+		rc = -ENODEV;
+		goto fail;
+	}
+
+	xdev_map[i] = 1;
+
+	mutex_unlock(&xdev_mutex);
+
+	xdev->index = i;
+
+	rc = xillyusb_setup_base_eps(xdev);
+
+	if (rc)
+		goto unindex_fail;
+
+	rc = xillyusb_discovery(interface);
+
+	if (rc)
+		goto unindex_fail;
+
+	mutex_lock(&xdev_mutex);
+	list_add_tail(&xdev->list_entry, &xdev_list);
+	mutex_unlock(&xdev_mutex);
+
+	return 0;
+
+unindex_fail:
+	xdev_map[i] = 0;
+
+fail:
+	usb_set_intfdata(interface, NULL);
+	kref_put(&xdev->kref, cleanup_dev);
+	return rc;
+}
+
+static void xillyusb_disconnect(struct usb_interface *interface)
+{
+	struct xillyusb_dev *xdev;
+
+	xillyusb_cleanup_chrdev(interface);
+
+	xdev = usb_get_intfdata(interface);
+
+	/*
+	 * Try to send OPCODE_QUIESCE, which will fail silently if the device
+	 * was disconnected, but makes sense on module unload.
+	 */
+
+	xillyusb_send_opcode(xdev, ~0, OPCODE_QUIESCE, 0);
+
+	usb_set_intfdata(interface, NULL);
+
+	report_io_error(xdev, -ENODEV);
+
+	mutex_lock(&xdev->io_mutex);
+	xdev->interface = NULL;
+	mutex_unlock(&xdev->io_mutex);
+
+	mutex_lock(&xdev_mutex);
+	xdev_map[xdev->index] = 0;
+	list_del(&xdev->list_entry);
+	mutex_unlock(&xdev_mutex);
+
+	kref_put(&xdev->kref, cleanup_dev);
+}
+
+static struct usb_driver xillyusb_driver = {
+	.name = xillyname,
+	.id_table = xillyusb_table,
+	.probe = xillyusb_probe,
+	.disconnect = xillyusb_disconnect,
+};
+
+static int __init xillyusb_init(void)
+{
+	int rc = 0;
+
+	int i;
+
+	if (LOG2_INITIAL_FIFO_BUF_SIZE > PAGE_SHIFT)
+		fifo_buf_order = LOG2_INITIAL_FIFO_BUF_SIZE - PAGE_SHIFT;
+	else
+		fifo_buf_order = 0;
+
+	for (i = 0; i < MAX_XILLYUSB_DEVS; i++)
+		xdev_map[i] = 0;
+
+	xillyusb_class = class_create(THIS_MODULE, xillyname);
+	if (IS_ERR(xillyusb_class)) {
+		rc = PTR_ERR(xillyusb_class);
+		pr_warn("Failed to register class xillyusb\n");
+
+		return rc;
+	}
+	rc = usb_register(&xillyusb_driver);
+
+	if (rc) {
+		class_destroy(xillyusb_class);
+		return rc;
+	}
+
+	return rc;
+}
+
+static void __exit xillyusb_exit(void)
+{
+	usb_deregister(&xillyusb_driver);
+	class_destroy(xillyusb_class);
+}
+
+module_init(xillyusb_init);
+module_exit(xillyusb_exit);
-- 
2.17.1