// 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/spinlock.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/crc32.h>
#include <linux/poll.h>
#include <linux/delay.h>
#include <linux/usb.h>

#include "xillybus_class.h"

MODULE_DESCRIPTION("Driver for XillyUSB FPGA IP Core");
MODULE_AUTHOR("Eli Billauer, Xillybus Ltd.");
MODULE_ALIAS("xillyusb");
MODULE_LICENSE("GPL v2");

#define XILLY_RX_TIMEOUT                (10 * HZ / 1000)
#define XILLY_RESPONSE_TIMEOUT          (500 * HZ / 1000)

#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";

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;

        int fill; /* Number of bytes in the FIFO */
        spinlock_t lock;
        wait_queue_head_t waitq;

        unsigned int readpos;
        unsigned int readbuf;
        unsigned int writepos;
        unsigned int writebuf;
        char **mem;
};

struct xillyusb_channel;

struct xillyusb_endpoint {
        struct xillyusb_dev *xdev;

        struct mutex ep_mutex; /* serialize operations on endpoint */

        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;
        bool drained;
        bool wake_on_drain;

        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, @in_fifo, bit fields below */

        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 @lock 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 device           *dev; /* For dev_err() and such */
        struct kref             kref;
        struct workqueue_struct *workq;

        int error;
        spinlock_t error_lock; /* protect @error */
        struct work_struct wakeup_workitem;

        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;
        unsigned long flags;
        int rc;

        nmax = fifo->size - READ_ONCE(fifo->fill);

        while (1) {
                unsigned int nrail = fifo->bufsize - writepos;
                unsigned int n = min(todo, nmax);

                if (n == 0) {
                        spin_lock_irqsave(&fifo->lock, flags);
                        fifo->fill += done;
                        spin_unlock_irqrestore(&fifo->lock, flags);

                        fifo->writepos = writepos;
                        fifo->writebuf = writebuf;

                        return done;
                }

                if (n > nrail)
                        n = nrail;

                rc = (*copier)(fifo->mem[writebuf] + writepos, data + done, n);

                if (rc)
                        return rc;

                done += n;
                todo -= n;

                writepos += n;
                nmax -= n;

                if (writepos == fifo->bufsize) {
                        writepos = 0;
                        writebuf++;

                        if (writebuf == fifo->bufnum)
                                writebuf = 0;
                }
        }
}

static 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;
        unsigned long flags;
        int rc;

        /*
         * The spinlock here is necessary, because otherwise fifo->fill
         * could have been increased by fifo_write() after writing data
         * to the buffer, but this data would potentially not have been
         * visible on this thread at the time the updated fifo->fill was.
         * That could lead to reading invalid data.
         */

        spin_lock_irqsave(&fifo->lock, flags);
        fill = fifo->fill;
        spin_unlock_irqrestore(&fifo->lock, flags);

        while (1) {
                unsigned int nrail = fifo->bufsize - readpos;
                unsigned int n = min(todo, fill);

                if (n == 0) {
                        spin_lock_irqsave(&fifo->lock, flags);
                        fifo->fill -= done;
                        spin_unlock_irqrestore(&fifo->lock, flags);

                        fifo->readpos = readpos;
                        fifo->readbuf = readbuf;

                        return done;
                }

                if (n > nrail)
                        n = nrail;

                rc = (*copier)(data + done, fifo->mem[readbuf] + readpos, n);

                if (rc)
                        return rc;

                done += n;
                todo -= n;

                readpos += n;
                fill -= n;

                if (readpos == fifo->bufsize) {
                        readpos = 0;
                        readbuf++;

                        if (readbuf == fifo->bufnum)
                                readbuf = 0;
                }
        }
}

/*
 * These three wrapper functions are used as the @copier argument to
 * fifo_write() and fifo_read(), so that they can work directly with
 * user memory as well.
 */

static int xilly_copy_from_user(void *dst, const void *src, int n)
{
        if (copy_from_user(dst, (const void __user *)src, n))
                return -EFAULT;

        return 0;
}

static int xilly_copy_to_user(void *dst, const void *src, int n)
{
        if (copy_to_user((void __user *)dst, src, n))
                return -EFAULT;

        return 0;
}

static int xilly_memcpy(void *dst, const void *src, int n)
{
        memcpy(dst, src, n);

        return 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;
        }

        fifo->fill = 0;
        fifo->readpos = 0;
        fifo->readbuf = 0;
        fifo->writepos = 0;
        fifo->writebuf = 0;
        spin_lock_init(&fifo->lock);
        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--;
                goto retry;
        } else {
                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);
}

/*
 * When endpoint_quiesce() returns, the endpoint has no URBs submitted,
 * won't accept any new URB submissions, and its related work item doesn't
 * and won't run anymore.
 */

static void endpoint_quiesce(struct xillyusb_endpoint *ep)
{
        mutex_lock(&ep->ep_mutex);
        ep->shutting_down = true;
        mutex_unlock(&ep->ep_mutex);

        usb_kill_anchored_urbs(&ep->anchor);
        cancel_work_sync(&ep->workitem);
}

/*
 * 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;

        fifo_mem_release(&ep->fifo);

        /* Join @filled_buffers with @buffers to free these entries too */
        list_splice(&ep->filled_buffers, &ep->buffers);

        list_for_each_safe(this, next, &ep->buffers) {
                struct xillybuffer *xb =
                        list_entry(this, struct xillybuffer, entry);

                free_pages((unsigned long)xb->buf, ep->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);
        mutex_init(&ep->ep_mutex);

        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->drained = true;
        ep->wake_on_drain = false;
        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);
}

/*
 * @process_in_mutex is taken to ensure that bulk_in_work() won't call
 * process_bulk_in() after wakeup_all()'s execution: The latter zeroes all
 * @read_data_ok entries, which will make process_bulk_in() report false
 * errors if executed. The mechanism relies on that xdev->error is assigned
 * a non-zero value by report_io_error() prior to queueing wakeup_all(),
 * which prevents bulk_in_work() from calling process_bulk_in().
 *
 * 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.
 */

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 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;

        mutex_lock(&ep->ep_mutex);

        if (ep->shutting_down || 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(&ep->ep_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 do_wake = false;

        mutex_lock(&ep->ep_mutex);

        if (ep->shutting_down || xdev->error)
                goto done;

        fill = READ_ONCE(fifo->fill) & ep->fill_mask;

        while (1) {
                int count;
                unsigned int max_read;

                spin_lock_irqsave(&ep->buffers_lock, flags);

                /*
                 * Race conditions might have the FIFO filled while the
                 * endpoint is marked as drained here. That doesn't matter,
                 * because the sole purpose of @drained is to ensure that
                 * certain data has been sent on the USB channel before
                 * shutting it down. Hence knowing that the FIFO appears
                 * to be empty with no outstanding URBs at some moment
                 * is good enough.
                 */

                if (!fill) {
                        ep->drained = !ep->outstanding_urbs;
                        if (ep->drained && ep->wake_on_drain)
                                do_wake = true;

                        spin_unlock_irqrestore(&ep->buffers_lock, flags);
                        goto done;
                }

                ep->drained = false;

                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;
                do_wake = 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(&ep->ep_mutex);

        if (do_wake)
                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;
        struct device *dev = xdev->dev;
        int chan_idx = chan_num >> 1;

        if (chan_idx >= xdev->num_channels) {
                dev_err(dev, "Received illegal channel ID %d from FPGA\n",
                        chan_num);
                return -EIO;
        }

        chan = &xdev->channels[chan_idx];

        switch (opcode) {
        case OPCODE_EOF:
                if (!chan->read_data_ok) {
                        dev_err(dev, "Received unexpected EOF for channel %d\n",
                                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:
                dev_err(dev, "Received illegal opcode %d from FPGA\n",
                        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;
        struct device *dev = xdev->dev;
        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) {
                dev_err(dev, "Received BULK IN transfer with %d bytes, not a multiple of 4\n",
                        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) {
                                dev_err(dev, "Expected opcode counter %d, got %d\n",
                                        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 ||
                    !xdev->channels[chan_idx].read_data_ok) {
                        dev_err(dev, "Received illegal channel ID %d from FPGA\n",
                                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)) {
                        dev_err(dev, "Misbehaving FPGA overflowed an upstream FIFO!\n");
                        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 (rc || list_empty(&ep->filled_buffers)) {
                        spin_unlock_irqrestore(&ep->buffers_lock, flags);
                        mutex_unlock(&xdev->process_in_mutex);

                        if (rc)
                                report_io_error(xdev, rc);
                        else 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);

                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 in the event of a bizarre hardware bug: Pull the USB plug.
         */

        while (wait_event_interruptible(fifo->waitq,
                                        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);
                                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)
{
        struct xillyusb_dev *xdev;
        struct xillyusb_channel *chan;
        struct xillyfifo *in_fifo = NULL;
        struct xillyusb_endpoint *out_ep = NULL;
        int rc;
        int index;

        rc = xillybus_find_inode(inode, (void **)&xdev, &index);
        if (rc)
                return rc;

        chan = &xdev->channels[index];
        filp->private_data = chan;

        mutex_lock(&chan->lock);

        rc = -ENODEV;

        if (xdev->error)
                goto unmutex_fail;

        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) {
                dev_err(xdev->dev,
                        "open() failed: O_NONBLOCK not allowed for read on this device\n");
                goto unmutex_fail;
        }

        if ((filp->f_flags & O_NONBLOCK) && (filp->f_mode & FMODE_WRITE) &&
            chan->out_synchronous) {
                dev_err(xdev->dev,
                        "open() failed: O_NONBLOCK not allowed for write on this device\n");
                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(&chan->lock);

        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);
                }

                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:
        chan->read_data_ok = 0;
        safely_assign_in_fifo(chan, NULL);
        fifo_mem_release(in_fifo);
        kfree(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(&chan->lock);

        if (filp->f_mode & FMODE_READ)
                chan->open_for_read = 0;

        if (filp->f_mode & FMODE_WRITE)
                chan->open_for_write = 0;

        mutex_unlock(&chan->lock);

        kref_put(&xdev->kref, cleanup_dev);

        return rc;

unmutex_fail:
        mutex_unlock(&chan->lock);
        return rc;
}

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 arithmetic 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 when
                 * fifo_read() returned, 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 (READ_ONCE(fifo->fill))
                                continue;

                        rc = 0;
                        break;
                }

                if (xdev->error) {
                        rc = xdev->error;
                        break;
                }

                if (filp->f_flags & O_NONBLOCK) {
                        rc = -EAGAIN;
                        break;
                }

                if (!sent_set_push) {
                        rc = xillyusb_send_opcode(xdev, chan_num,
                                                  OPCODE_SET_PUSH,
                                                  complete_checkpoint);

                        if (rc)
                                break;

                        sent_set_push = true;
                }

                if (left_to_sleep > 0) {
                        /*
                         * 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,
                                 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,
                                 fifo->fill || !chan->read_data_ok);
                }

                if (rc < 0) {
                        rc = -EINTR;
                        break;
                }
        }

        if (((filp->f_flags & O_NONBLOCK) || chan->poll_used) &&
            !READ_ONCE(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);

        mutex_unlock(&chan->out_mutex);

        if (rc == -ETIMEDOUT) {
                /* The things you do to use dev_warn() and not pr_warn() */
                struct xillyusb_dev *xdev = chan->xdev;

                mutex_lock(&chan->lock);
                if (!xdev->error)
                        dev_warn(xdev->dev,
                                 "Timed out while flushing. Output data may be lost.\n");
                mutex_unlock(&chan->lock);
        }

        return rc;
}

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,
                     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);
                kfree(in_fifo);

                mutex_lock(&chan->lock);
                chan->open_for_read = 0;
                mutex_unlock(&chan->lock);
        }

        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_quiesce(ep);
                endpoint_dealloc(ep);

                /* See comments on rc_read above */
                rc_write = xillyusb_send_opcode(xdev, chan->chan_idx << 1,
                                                OPCODE_CLOSE, 0);

                mutex_lock(&chan->lock);
                chan->open_for_write = 0;
                mutex_unlock(&chan->lock);
        }

        kref_put(&xdev->kref, cleanup_dev);

        return rc_read ? rc_read : rc_write;
}

/*
 * Xillybus' API allows device nodes to be seekable, giving the user
 * application access to a RAM array on the FPGA (or logic emulating it).
 */

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 SEEK_SET:
                pos = offset;
                break;
        case SEEK_CUR:
                pos += offset;
                break;
        case SEEK_END:
                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 (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 &&
            (READ_ONCE(chan->in_fifo->fill) || !chan->read_data_ok))
                mask |= EPOLLIN | EPOLLRDNORM;

        if (chan->out_ep &&
            (READ_ONCE(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,
};

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,
                          int num_channels)
{
        struct xillyusb_channel *chan;
        int i;

        chan = kcalloc(num_channels, sizeof(*chan), GFP_KERNEL);
        if (!chan)
                return -ENOMEM;

        xdev->channels = chan;

        for (i = 0; i < 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;
                }

                /*
                 * A downstream channel should never exist above index 13,
                 * as it would request a nonexistent BULK endpoint > 15.
                 * In the peculiar case that it does, it's ignored silently.
                 */

                if ((out_desc & 0x80) && i < 14) { /* 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;
        int num_channels;

        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 */
        bogus_chandesc[0] = cpu_to_le16(0x80);
        bogus_chandesc[1] = cpu_to_le16(0);

        rc = setup_channels(xdev, bogus_chandesc, 1);

        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;

        xdev->num_channels = 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 = READ_ONCE(idt_fifo.fill);
        idt = kmalloc(idt_len, GFP_KERNEL);

        if (!idt) {
                rc = -ENOMEM;
                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 upgrade. Aborting.\n",
                        (int)*idt);
                rc = -ENODEV;
                goto unidt;
        }

        /* Phase II: Set up the streams as defined in IDT */

        num_channels = le16_to_cpu(*((__le16 *)(idt + 1)));
        names_offset = 3 + 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, num_channels);

        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->channels
         * is updated on anything that might run in parallel, flush the
         * workqueue, which rarely does anything.
         */
        flush_workqueue(xdev->workq);

        xdev->num_channels = num_channels;

        fifo_mem_release(&idt_fifo);
        kfree(chan);

        rc = xillybus_init_chrdev(&interface->dev, &xillyusb_fops,
                                  THIS_MODULE, xdev,
                                  idt + names_offset,
                                  idt_len - names_offset,
                                  num_channels,
                                  xillyname, true);

        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;

        xdev = kzalloc(sizeof(*xdev), GFP_KERNEL);
        if (!xdev)
                return -ENOMEM;

        kref_init(&xdev->kref);
        mutex_init(&xdev->process_in_mutex);
        mutex_init(&xdev->msg_mutex);

        xdev->udev = usb_get_dev(interface_to_usbdev(interface));
        xdev->dev = &interface->dev;
        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);

        rc = xillyusb_setup_base_eps(xdev);
        if (rc)
                goto fail;

        rc = xillyusb_discovery(interface);
        if (rc)
                goto latefail;

        return 0;

latefail:
        endpoint_quiesce(xdev->in_ep);
        endpoint_quiesce(xdev->msg_ep);

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 = usb_get_intfdata(interface);
        struct xillyusb_endpoint *msg_ep = xdev->msg_ep;
        struct xillyfifo *fifo = &msg_ep->fifo;
        int rc;
        int i;

        xillybus_cleanup_chrdev(xdev, &interface->dev);

        /*
         * Try to send OPCODE_QUIESCE, which will fail silently if the device
         * was disconnected, but makes sense on module unload.
         */

        msg_ep->wake_on_drain = true;
        xillyusb_send_opcode(xdev, ~0, OPCODE_QUIESCE, 0);

        /*
         * If the device has been disconnected, sending the opcode causes
         * a global device error with xdev->error, if such error didn't
         * occur earlier. Hence timing out means that the USB link is fine,
         * but somehow the message wasn't sent. Should never happen.
         */

        rc = wait_event_interruptible_timeout(fifo->waitq,
                                              msg_ep->drained || xdev->error,
                                              XILLY_RESPONSE_TIMEOUT);

        if (!rc)
                dev_err(&interface->dev,
                        "Weird timeout condition on sending quiesce request.\n");

        report_io_error(xdev, -ENODEV); /* Discourage further activity */

        /*
         * This device driver is declared with soft_unbind set, or else
         * sending OPCODE_QUIESCE above would always fail. The price is
         * that the USB framework didn't kill outstanding URBs, so it has
         * to be done explicitly before returning from this call.
         */

        for (i = 0; i < xdev->num_channels; i++) {
                struct xillyusb_channel *chan = &xdev->channels[i];

                /*
                 * Lock taken to prevent chan->out_ep from changing. It also
                 * ensures xillyusb_open() and xillyusb_flush() don't access
                 * xdev->dev after being nullified below.
                 */
                mutex_lock(&chan->lock);
                if (chan->out_ep)
                        endpoint_quiesce(chan->out_ep);
                mutex_unlock(&chan->lock);
        }

        endpoint_quiesce(xdev->in_ep);
        endpoint_quiesce(xdev->msg_ep);

        usb_set_intfdata(interface, NULL);

        xdev->dev = NULL;

        kref_put(&xdev->kref, cleanup_dev);
}

static struct usb_driver xillyusb_driver = {
        .name = xillyname,
        .id_table = xillyusb_table,
        .probe = xillyusb_probe,
        .disconnect = xillyusb_disconnect,
        .soft_unbind = 1,
};

static int __init xillyusb_init(void)
{
        int rc = 0;

        if (LOG2_INITIAL_FIFO_BUF_SIZE > PAGE_SHIFT)
                fifo_buf_order = LOG2_INITIAL_FIFO_BUF_SIZE - PAGE_SHIFT;
        else
                fifo_buf_order = 0;

        rc = usb_register(&xillyusb_driver);

        return rc;
}

static void __exit xillyusb_exit(void)
{
        usb_deregister(&xillyusb_driver);
}

module_init(xillyusb_init);
module_exit(xillyusb_exit);