usb: gadget/uvc: Port UVC webcam gadget to use videobuf2 framework

This patch reworks the videobuffer management logic present in the UVC
webcam gadget and ports it to use the "more apt" videobuf2 framework for
video buffer management.

To support routing video data captured from a real V4L2 video capture
device with a "zero copy" operation on videobuffers (as they pass from
the V4L2 domain to UVC domain via a user-space application), we need to
support USER_PTR IO method at the UVC gadget side.

So the V4L2 capture device driver can still continue to use MMAP IO
method and now the user-space application can just pass a pointer to the
video buffers being dequeued from the V4L2 device side while queueing
them at the UVC gadget end. This ensures that we have a "zero-copy"
design as the videobuffers pass from the V4L2 capture device to the UVC
gadget.

Note that there will still be a need to apply UVC specific payload
headers on top of each UVC payload data, which will still require a copy
operation to be performed in the 'encode' routines of the UVC gadget.

This patch also addresses one issue found out while porting the UVC
gadget to videobuf2 framework:
	- In case the usb requests queued by the gadget get completed
	  with a status of -ESHUTDOWN (disconnected from host),
	  the queue of videobuf2 should be cancelled to ensure that the
	  application space daemon is not left in a state waiting for
	  a vb2 to be successfully absorbed at the USB side.

Signed-off-by: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 159 insertions, 373 deletions

diff --git a/drivers/usb/gadget/uvc_queue.c b/drivers/usb/gadget/uvc_queue.c
index 104ae9c81251..31397954c889 100644
--- a/drivers/usb/gadget/uvc_queue.c
+++ b/drivers/usb/gadget/uvc_queue.c
@@ -10,6 +10,7 @@
  *      (at your option) any later version.
  */
 
+#include <linux/atomic.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/list.h>
@@ -18,7 +19,8 @@
 #include <linux/videodev2.h>
 #include <linux/vmalloc.h>
 #include <linux/wait.h>
-#include <linux/atomic.h>
+
+#include <media/videobuf2-vmalloc.h>
 
 #include "uvc.h"
 
@@ -28,330 +30,175 @@
  * Video queues is initialized by uvc_queue_init(). The function performs
  * basic initialization of the uvc_video_queue struct and never fails.
  *
- * Video buffer allocation and freeing are performed by uvc_alloc_buffers and
- * uvc_free_buffers respectively. The former acquires the video queue lock,
- * while the later must be called with the lock held (so that allocation can
- * free previously allocated buffers). Trying to free buffers that are mapped
- * to user space will return -EBUSY.
- *
- * Video buffers are managed using two queues. However, unlike most USB video
- * drivers that use an in queue and an out queue, we use a main queue to hold
- * all queued buffers (both 'empty' and 'done' buffers), and an irq queue to
- * hold empty buffers. This design (copied from video-buf) minimizes locking
- * in interrupt, as only one queue is shared between interrupt and user
- * contexts.
- *
- * Use cases
- * ---------
- *
- * Unless stated otherwise, all operations that modify the irq buffers queue
- * are protected by the irq spinlock.
- *
- * 1. The user queues the buffers, starts streaming and dequeues a buffer.
- *
- *    The buffers are added to the main and irq queues. Both operations are
- *    protected by the queue lock, and the later is protected by the irq
- *    spinlock as well.
- *
- *    The completion handler fetches a buffer from the irq queue and fills it
- *    with video data. If no buffer is available (irq queue empty), the handler
- *    returns immediately.
- *
- *    When the buffer is full, the completion handler removes it from the irq
- *    queue, marks it as ready (UVC_BUF_STATE_DONE) and wakes its wait queue.
- *    At that point, any process waiting on the buffer will be woken up. If a
- *    process tries to dequeue a buffer after it has been marked ready, the
- *    dequeing will succeed immediately.
- *
- * 2. Buffers are queued, user is waiting on a buffer and the device gets
- *    disconnected.
- *
- *    When the device is disconnected, the kernel calls the completion handler
- *    with an appropriate status code. The handler marks all buffers in the
- *    irq queue as being erroneous (UVC_BUF_STATE_ERROR) and wakes them up so
- *    that any process waiting on a buffer gets woken up.
- *
- *    Waking up up the first buffer on the irq list is not enough, as the
- *    process waiting on the buffer might restart the dequeue operation
- *    immediately.
- *
+ * Video buffers are managed by videobuf2. The driver uses a mutex to protect
+ * the videobuf2 queue operations by serializing calls to videobuf2 and a
+ * spinlock to protect the IRQ queue that holds the buffers to be processed by
+ * the driver.
  */
 
-static void
-uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type)
-{
-        mutex_init(&queue->mutex);
-        spin_lock_init(&queue->irqlock);
-        INIT_LIST_HEAD(&queue->mainqueue);
-        INIT_LIST_HEAD(&queue->irqqueue);
-        queue->type = type;
-}
-
-/*
- * Free the video buffers.
- *
- * This function must be called with the queue lock held.
+/* -----------------------------------------------------------------------------
+ * videobuf2 queue operations
  */
-static int uvc_free_buffers(struct uvc_video_queue *queue)
+
+static int uvc_queue_setup(struct vb2_queue *vq, const struct v4l2_format *fmt,
+                           unsigned int *nbuffers, unsigned int *nplanes,
+                           unsigned int sizes[], void *alloc_ctxs[])
 {
-        unsigned int i;
+        struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
+        struct uvc_video *video = container_of(queue, struct uvc_video, queue);
 
-        for (i = 0; i < queue->count; ++i) {
-                if (queue->buffer[i].vma_use_count != 0)
-                        return -EBUSY;
-        }
+        if (*nbuffers > UVC_MAX_VIDEO_BUFFERS)
+                *nbuffers = UVC_MAX_VIDEO_BUFFERS;
 
-        if (queue->count) {
-                vfree(queue->mem);
-                queue->count = 0;
-        }
+        *nplanes = 1;
+
+        sizes[0] = video->imagesize;
 
         return 0;
 }
 
-/*
- * Allocate the video buffers.
- *
- * Pages are reserved to make sure they will not be swapped, as they will be
- * filled in the URB completion handler.
- *
- * Buffers will be individually mapped, so they must all be page aligned.
- */
-static int
-uvc_alloc_buffers(struct uvc_video_queue *queue, unsigned int nbuffers,
-                  unsigned int buflength)
+static int uvc_buffer_prepare(struct vb2_buffer *vb)
 {
-        unsigned int bufsize = PAGE_ALIGN(buflength);
-        unsigned int i;
-        void *mem = NULL;
-        int ret;
+        struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
+        struct uvc_buffer *buf = container_of(vb, struct uvc_buffer, buf);
 
-        if (nbuffers > UVC_MAX_VIDEO_BUFFERS)
-                nbuffers = UVC_MAX_VIDEO_BUFFERS;
+        if (vb->v4l2_buf.type == V4L2_BUF_TYPE_VIDEO_OUTPUT &&
+            vb2_get_plane_payload(vb, 0) > vb2_plane_size(vb, 0)) {
+                uvc_trace(UVC_TRACE_CAPTURE, "[E] Bytes used out of bounds.\n");
+                return -EINVAL;
+        }
 
-        mutex_lock(&queue->mutex);
+        if (unlikely(queue->flags & UVC_QUEUE_DISCONNECTED))
+                return -ENODEV;
 
-        if ((ret = uvc_free_buffers(queue)) < 0)
-                goto done;
+        buf->state = UVC_BUF_STATE_QUEUED;
+        buf->mem = vb2_plane_vaddr(vb, 0);
+        buf->length = vb2_plane_size(vb, 0);
+        if (vb->v4l2_buf.type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
+                buf->bytesused = 0;
+        else
+                buf->bytesused = vb2_get_plane_payload(vb, 0);
 
-        /* Bail out if no buffers should be allocated. */
-        if (nbuffers == 0)
-                goto done;
+        return 0;
+}
 
-        /* Decrement the number of buffers until allocation succeeds. */
-        for (; nbuffers > 0; --nbuffers) {
-                mem = vmalloc_32(nbuffers * bufsize);
-                if (mem != NULL)
-                        break;
-        }
+static void uvc_buffer_queue(struct vb2_buffer *vb)
+{
+        struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
+        struct uvc_buffer *buf = container_of(vb, struct uvc_buffer, buf);
+        unsigned long flags;
 
-        if (mem == NULL) {
-                ret = -ENOMEM;
-                goto done;
-        }
+        spin_lock_irqsave(&queue->irqlock, flags);
 
-        for (i = 0; i < nbuffers; ++i) {
-                memset(&queue->buffer[i], 0, sizeof queue->buffer[i]);
-                queue->buffer[i].buf.index = i;
-                queue->buffer[i].buf.m.offset = i * bufsize;
-                queue->buffer[i].buf.length = buflength;
-                queue->buffer[i].buf.type = queue->type;
-                queue->buffer[i].buf.sequence = 0;
-                queue->buffer[i].buf.field = V4L2_FIELD_NONE;
-                queue->buffer[i].buf.memory = V4L2_MEMORY_MMAP;
-                queue->buffer[i].buf.flags = 0;
-                init_waitqueue_head(&queue->buffer[i].wait);
+        if (likely(!(queue->flags & UVC_QUEUE_DISCONNECTED))) {
+                list_add_tail(&buf->queue, &queue->irqqueue);
+        } else {
+                /* If the device is disconnected return the buffer to userspace
+                 * directly. The next QBUF call will fail with -ENODEV.
+                 */
+                buf->state = UVC_BUF_STATE_ERROR;
+                vb2_buffer_done(&buf->buf, VB2_BUF_STATE_ERROR);
         }
 
-        queue->mem = mem;
-        queue->count = nbuffers;
-        queue->buf_size = bufsize;
-        ret = nbuffers;
-
-done:
-        mutex_unlock(&queue->mutex);
-        return ret;
+        spin_unlock_irqrestore(&queue->irqlock, flags);
 }
 
-static void __uvc_query_buffer(struct uvc_buffer *buf,
-                struct v4l2_buffer *v4l2_buf)
-{
-        memcpy(v4l2_buf, &buf->buf, sizeof *v4l2_buf);
-
-        if (buf->vma_use_count)
-                v4l2_buf->flags |= V4L2_BUF_FLAG_MAPPED;
-
-        switch (buf->state) {
-        case UVC_BUF_STATE_ERROR:
-        case UVC_BUF_STATE_DONE:
-                v4l2_buf->flags |= V4L2_BUF_FLAG_DONE;
-                break;
-        case UVC_BUF_STATE_QUEUED:
-        case UVC_BUF_STATE_ACTIVE:
-                v4l2_buf->flags |= V4L2_BUF_FLAG_QUEUED;
-                break;
-        case UVC_BUF_STATE_IDLE:
-        default:
-                break;
-        }
-}
+static struct vb2_ops uvc_queue_qops = {
+        .queue_setup = uvc_queue_setup,
+        .buf_prepare = uvc_buffer_prepare,
+        .buf_queue = uvc_buffer_queue,
+};
 
-static int
-uvc_query_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf)
+static int uvc_queue_init(struct uvc_video_queue *queue,
+                          enum v4l2_buf_type type)
 {
-        int ret = 0;
+        int ret;
 
-        mutex_lock(&queue->mutex);
-        if (v4l2_buf->index >= queue->count) {
-                ret = -EINVAL;
-                goto done;
-        }
+        queue->queue.type = type;
+        queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
+        queue->queue.drv_priv = queue;
+        queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
+        queue->queue.ops = &uvc_queue_qops;
+        queue->queue.mem_ops = &vb2_vmalloc_memops;
+        ret = vb2_queue_init(&queue->queue);
+        if (ret)
+                return ret;
+
+        mutex_init(&queue->mutex);
+        spin_lock_init(&queue->irqlock);
+        INIT_LIST_HEAD(&queue->irqqueue);
+        queue->flags = 0;
 
-        __uvc_query_buffer(&queue->buffer[v4l2_buf->index], v4l2_buf);
+        return 0;
+}
 
-done:
+/*
+ * Free the video buffers.
+ */
+static void uvc_free_buffers(struct uvc_video_queue *queue)
+{
+        mutex_lock(&queue->mutex);
+        vb2_queue_release(&queue->queue);
         mutex_unlock(&queue->mutex);
-        return ret;
 }
 
 /*
- * Queue a video buffer. Attempting to queue a buffer that has already been
- * queued will return -EINVAL.
+ * Allocate the video buffers.
  */
-static int
-uvc_queue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf)
+static int uvc_alloc_buffers(struct uvc_video_queue *queue,
+                             struct v4l2_requestbuffers *rb)
 {
-        struct uvc_buffer *buf;
-        unsigned long flags;
-        int ret = 0;
+        int ret;
 
-        uvc_trace(UVC_TRACE_CAPTURE, "Queuing buffer %u.\n", v4l2_buf->index);
+        mutex_lock(&queue->mutex);
+        ret = vb2_reqbufs(&queue->queue, rb);
+        mutex_unlock(&queue->mutex);
 
-        if (v4l2_buf->type != queue->type ||
-            v4l2_buf->memory != V4L2_MEMORY_MMAP) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer type (%u) "
-                        "and/or memory (%u).\n", v4l2_buf->type,
-                        v4l2_buf->memory);
-                return -EINVAL;
-        }
+        return ret ? ret : rb->count;
+}
 
-        mutex_lock(&queue->mutex);
-        if (v4l2_buf->index >= queue->count) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Out of range index.\n");
-                ret = -EINVAL;
-                goto done;
-        }
+static int uvc_query_buffer(struct uvc_video_queue *queue,
+                            struct v4l2_buffer *buf)
+{
+        int ret;
 
-        buf = &queue->buffer[v4l2_buf->index];
-        if (buf->state != UVC_BUF_STATE_IDLE) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state "
-                        "(%u).\n", buf->state);
-                ret = -EINVAL;
-                goto done;
-        }
+        mutex_lock(&queue->mutex);
+        ret = vb2_querybuf(&queue->queue, buf);
+        mutex_unlock(&queue->mutex);
 
-        if (v4l2_buf->type == V4L2_BUF_TYPE_VIDEO_OUTPUT &&
-            v4l2_buf->bytesused > buf->buf.length) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Bytes used out of bounds.\n");
-                ret = -EINVAL;
-                goto done;
-        }
+        return ret;
+}
 
-        if (v4l2_buf->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
-                buf->buf.bytesused = 0;
-        else
-                buf->buf.bytesused = v4l2_buf->bytesused;
+static int uvc_queue_buffer(struct uvc_video_queue *queue,
+                            struct v4l2_buffer *buf)
+{
+        unsigned long flags;
+        int ret;
 
+        mutex_lock(&queue->mutex);
+        ret = vb2_qbuf(&queue->queue, buf);
         spin_lock_irqsave(&queue->irqlock, flags);
-        if (queue->flags & UVC_QUEUE_DISCONNECTED) {
-                spin_unlock_irqrestore(&queue->irqlock, flags);
-                ret = -ENODEV;
-                goto done;
-        }
-        buf->state = UVC_BUF_STATE_QUEUED;
-
         ret = (queue->flags & UVC_QUEUE_PAUSED) != 0;
         queue->flags &= ~UVC_QUEUE_PAUSED;
-
-        list_add_tail(&buf->stream, &queue->mainqueue);
-        list_add_tail(&buf->queue, &queue->irqqueue);
         spin_unlock_irqrestore(&queue->irqlock, flags);
-
-done:
         mutex_unlock(&queue->mutex);
-        return ret;
-}
-
-static int uvc_queue_waiton(struct uvc_buffer *buf, int nonblocking)
-{
-        if (nonblocking) {
-                return (buf->state != UVC_BUF_STATE_QUEUED &&
-                        buf->state != UVC_BUF_STATE_ACTIVE)
-                        ? 0 : -EAGAIN;
-        }
 
-        return wait_event_interruptible(buf->wait,
-                buf->state != UVC_BUF_STATE_QUEUED &&
-                buf->state != UVC_BUF_STATE_ACTIVE);
+        return ret;
 }
 
 /*
  * Dequeue a video buffer. If nonblocking is false, block until a buffer is
  * available.
  */
-static int
-uvc_dequeue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf,
-                   int nonblocking)
+static int uvc_dequeue_buffer(struct uvc_video_queue *queue,
+                              struct v4l2_buffer *buf, int nonblocking)
 {
-        struct uvc_buffer *buf;
-        int ret = 0;
-
-        if (v4l2_buf->type != queue->type ||
-            v4l2_buf->memory != V4L2_MEMORY_MMAP) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer type (%u) "
-                        "and/or memory (%u).\n", v4l2_buf->type,
-                        v4l2_buf->memory);
-                return -EINVAL;
-        }
+        int ret;
 
         mutex_lock(&queue->mutex);
-        if (list_empty(&queue->mainqueue)) {
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Empty buffer queue.\n");
-                ret = -EINVAL;
-                goto done;
-        }
-
-        buf = list_first_entry(&queue->mainqueue, struct uvc_buffer, stream);
-        if ((ret = uvc_queue_waiton(buf, nonblocking)) < 0)
-                goto done;
-
-        uvc_trace(UVC_TRACE_CAPTURE, "Dequeuing buffer %u (%u, %u bytes).\n",
-                buf->buf.index, buf->state, buf->buf.bytesused);
-
-        switch (buf->state) {
-        case UVC_BUF_STATE_ERROR:
-                uvc_trace(UVC_TRACE_CAPTURE, "[W] Corrupted data "
-                        "(transmission error).\n");
-                ret = -EIO;
-        case UVC_BUF_STATE_DONE:
-                buf->state = UVC_BUF_STATE_IDLE;
-                break;
-
-        case UVC_BUF_STATE_IDLE:
-        case UVC_BUF_STATE_QUEUED:
-        case UVC_BUF_STATE_ACTIVE:
-        default:
-                uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state %u "
-                        "(driver bug?).\n", buf->state);
-                ret = -EINVAL;
-                goto done;
-        }
-
-        list_del(&buf->stream);
-        __uvc_query_buffer(buf, v4l2_buf);
-
-done:
+        ret = vb2_dqbuf(&queue->queue, buf, nonblocking);
         mutex_unlock(&queue->mutex);
+
         return ret;
 }
 
@@ -361,103 +208,27 @@ done:
  * This function implements video queue polling and is intended to be used by
  * the device poll handler.
  */
-static unsigned int
-uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
-               poll_table *wait)
+static unsigned int uvc_queue_poll(struct uvc_video_queue *queue,
+                                   struct file *file, poll_table *wait)
 {
-        struct uvc_buffer *buf;
-        unsigned int mask = 0;
+        unsigned int ret;
 
         mutex_lock(&queue->mutex);
-        if (list_empty(&queue->mainqueue))
-                goto done;
-
-        buf = list_first_entry(&queue->mainqueue, struct uvc_buffer, stream);
-
-        poll_wait(file, &buf->wait, wait);
-        if (buf->state == UVC_BUF_STATE_DONE ||
-            buf->state == UVC_BUF_STATE_ERROR)
-                mask |= POLLOUT | POLLWRNORM;
-
-done:
+        ret = vb2_poll(&queue->queue, file, wait);
         mutex_unlock(&queue->mutex);
-        return mask;
-}
 
-/*
- * VMA operations.
- */
-static void uvc_vm_open(struct vm_area_struct *vma)
-{
-        struct uvc_buffer *buffer = vma->vm_private_data;
-        buffer->vma_use_count++;
-}
-
-static void uvc_vm_close(struct vm_area_struct *vma)
-{
-        struct uvc_buffer *buffer = vma->vm_private_data;
-        buffer->vma_use_count--;
+        return ret;
 }
 
-static struct vm_operations_struct uvc_vm_ops = {
-        .open           = uvc_vm_open,
-        .close          = uvc_vm_close,
-};
-
-/*
- * Memory-map a buffer.
- *
- * This function implements video buffer memory mapping and is intended to be
- * used by the device mmap handler.
- */
-static int
-uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
+static int uvc_queue_mmap(struct uvc_video_queue *queue,
+                          struct vm_area_struct *vma)
 {
-        struct uvc_buffer *uninitialized_var(buffer);
-        struct page *page;
-        unsigned long addr, start, size;
-        unsigned int i;
-        int ret = 0;
-
-        start = vma->vm_start;
-        size = vma->vm_end - vma->vm_start;
+        int ret;
 
         mutex_lock(&queue->mutex);
-
-        for (i = 0; i < queue->count; ++i) {
-                buffer = &queue->buffer[i];
-                if ((buffer->buf.m.offset >> PAGE_SHIFT) == vma->vm_pgoff)
-                        break;
-        }
-
-        if (i == queue->count || size != queue->buf_size) {
-                ret = -EINVAL;
-                goto done;
-        }
-
-        /*
-         * VM_IO marks the area as being an mmaped region for I/O to a
-         * device. It also prevents the region from being core dumped.
-         */
-        vma->vm_flags |= VM_IO;
-
-        addr = (unsigned long)queue->mem + buffer->buf.m.offset;
-        while (size > 0) {
-                page = vmalloc_to_page((void *)addr);
-                if ((ret = vm_insert_page(vma, start, page)) < 0)
-                        goto done;
-
-                start += PAGE_SIZE;
-                addr += PAGE_SIZE;
-                size -= PAGE_SIZE;
-        }
-
-        vma->vm_ops = &uvc_vm_ops;
-        vma->vm_private_data = buffer;
-        uvc_vm_open(vma);
-
-done:
+        ret = vb2_mmap(&queue->queue, vma);
         mutex_unlock(&queue->mutex);
+
         return ret;
 }
 
@@ -484,7 +255,7 @@ static void uvc_queue_cancel(struct uvc_video_queue *queue, int disconnect)
                                        queue);
                 list_del(&buf->queue);
                 buf->state = UVC_BUF_STATE_ERROR;
-                wake_up(&buf->wait);
+                vb2_buffer_done(&buf->buf, VB2_BUF_STATE_ERROR);
         }
         /* This must be protected by the irqlock spinlock to avoid race
          * conditions between uvc_queue_buffer and the disconnection event that
@@ -516,26 +287,33 @@ static void uvc_queue_cancel(struct uvc_video_queue *queue, int disconnect)
  */
 static int uvc_queue_enable(struct uvc_video_queue *queue, int enable)
 {
-        unsigned int i;
+        unsigned long flags;
         int ret = 0;
 
         mutex_lock(&queue->mutex);
         if (enable) {
-                if (uvc_queue_streaming(queue)) {
-                        ret = -EBUSY;
+                ret = vb2_streamon(&queue->queue, queue->queue.type);
+                if (ret < 0)
                         goto done;
-                }
+
                 queue->sequence = 0;
-                queue->flags |= UVC_QUEUE_STREAMING;
                 queue->buf_used = 0;
         } else {
-                uvc_queue_cancel(queue, 0);
-                INIT_LIST_HEAD(&queue->mainqueue);
+                ret = vb2_streamoff(&queue->queue, queue->queue.type);
+                if (ret < 0)
+                        goto done;
 
-                for (i = 0; i < queue->count; ++i)
-                        queue->buffer[i].state = UVC_BUF_STATE_IDLE;
+                spin_lock_irqsave(&queue->irqlock, flags);
+                INIT_LIST_HEAD(&queue->irqqueue);
 
-                queue->flags &= ~UVC_QUEUE_STREAMING;
+                /*
+                 * FIXME: We need to clear the DISCONNECTED flag to ensure that
+                 * applications will be able to queue buffers for the next
+                 * streaming run. However, clearing it here doesn't guarantee
+                 * that the device will be reconnected in the meantime.
+                 */
+                queue->flags &= ~UVC_QUEUE_DISCONNECTED;
+                spin_unlock_irqrestore(&queue->irqlock, flags);
         }
 
 done:
@@ -544,15 +322,15 @@ done:
 }
 
 /* called with &queue_irqlock held.. */
-static struct uvc_buffer *
-uvc_queue_next_buffer(struct uvc_video_queue *queue, struct uvc_buffer *buf)
+static struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
+                                                struct uvc_buffer *buf)
 {
         struct uvc_buffer *nextbuf;
 
         if ((queue->flags & UVC_QUEUE_DROP_INCOMPLETE) &&
-            buf->buf.length != buf->buf.bytesused) {
+             buf->length != buf->bytesused) {
                 buf->state = UVC_BUF_STATE_QUEUED;
-                buf->buf.bytesused = 0;
+                vb2_set_plane_payload(&buf->buf, 0, 0);
                 return buf;
         }
 
@@ -563,10 +341,18 @@ uvc_queue_next_buffer(struct uvc_video_queue *queue, struct uvc_buffer *buf)
         else
                 nextbuf = NULL;
 
-        buf->buf.sequence = queue->sequence++;
-        do_gettimeofday(&buf->buf.timestamp);
+        /*
+         * FIXME: with videobuf2, the sequence number or timestamp fields
+         * are valid only for video capture devices and the UVC gadget usually
+         * is a video output device. Keeping these until the specs are clear on
+         * this aspect.
+         */
+        buf->buf.v4l2_buf.sequence = queue->sequence++;
+        do_gettimeofday(&buf->buf.v4l2_buf.timestamp);
+
+        vb2_set_plane_payload(&buf->buf, 0, buf->bytesused);
+        vb2_buffer_done(&buf->buf, VB2_BUF_STATE_DONE);
 
-        wake_up(&buf->wait);
         return nextbuf;
 }