Message-ID: <20180509103639.GC39838@e107564-lin.cambridge.arm.com>
Date:   Wed, 9 May 2018 11:36:40 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     linux-media@...r.kernel.org, kernel@...labora.com,
        Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v9 11/15] vb2: add in-fence support to QBUF

Hi Ezequiel,

On Fri, May 04, 2018 at 05:06:08PM -0300, Ezequiel Garcia wrote:
>From: Gustavo Padovan <gustavo.padovan@...labora.com>
>
>Receive in-fence from userspace and add support for waiting on them
>before queueing the buffer to the driver. Buffers can't be queued to the
>driver before its fences signal. And a buffer can't be queued to the driver
>out of the order they were queued from userspace. That means that even if
>its fence signals it must wait for all other buffers, ahead of it in the queue,
>to signal first.
>
>If the fence for some buffer fails we do not queue it to the driver,
>instead we mark it as error and wait until the previous buffer is done
>to notify userspace of the error. We wait here to deliver the buffers back
>to userspace in order.
>
>v12: fixed dvb_vb2.c usage of vb2_core_qbuf.
>
>v11: - minor doc/comments fixes (Hans Verkuil)
>     - reviewed the in-fence path at __fill_v4l2_buffer()
>
>v10: - rename fence to in_fence in many places
>     - handle fences signalling with error better (Hans Verkuil)
>
>v9: - improve comments and docs (Hans Verkuil)
>    - fix unlocking of vb->fence_cb_lock on vb2_core_qbuf (Hans Verkuil)
>    - move in-fences code that was in the out-fences patch here (Alex)
>
>v8: - improve comments about fences with errors
>
>v7: - get rid of the fence array stuff for ordering and just use
>      get_num_buffers_ready() (Hans)
>    - fix issue of queuing the buffer twice (Hans)
>    - avoid the dma_fence_wait() in core_qbuf() (Alex)
>    - merge preparation commit in
>
>v6: - With fences always keep the order userspace queues the buffers.
>    - Protect in_fence manipulation with a lock (Brian Starkey)
>    - check if fences have the same context before adding a fence array
>    - Fix last_fence ref unbalance in __set_in_fence() (Brian Starkey)
>    - Clean up fence if __set_in_fence() fails (Brian Starkey)
>    - treat -EINVAL from dma_fence_add_callback() (Brian Starkey)
>
>v5: - use fence_array to keep buffers ordered in vb2 core when
>      needed (Brian Starkey)
>    - keep backward compat on the reserved2 field (Brian Starkey)
>    - protect fence callback removal with lock (Brian Starkey)
>
>v4: - Add a comment about dma_fence_add_callback() not returning a
>      error (Hans)
>    - Call dma_fence_put(vb->in_fence) if fence signaled (Hans)
>    - select SYNC_FILE under config VIDEOBUF2_CORE (Hans)
>    - Move dma_fence_is_signaled() check to __enqueue_in_driver() (Hans)
>    - Remove list_for_each_entry() in __vb2_core_qbuf() (Hans)
>    - Remove if (vb->state != VB2_BUF_STATE_QUEUED) from
>      vb2_start_streaming() (Hans)
>    - set IN_FENCE flags on __fill_v4l2_buffer (Hans)
>    - Queue buffers to the driver as soon as they are ready (Hans)
>    - call fill_user_buffer() after queuing the buffer (Hans)
>    - add err: label to clean up fence
>    - add dma_fence_wait() before calling vb2_start_streaming()
>
>v3: - document fence parameter
>    - remove ternary if at vb2_qbuf() return (Mauro)
>    - do not change if conditions behaviour (Mauro)
>
>v2: - fix vb2_queue_or_prepare_buf() ret check
>    - remove check for VB2_MEMORY_DMABUF only (Javier)
>    - check num of ready buffers to start streaming
>    - when queueing, start from the first ready buffer
>    - handle queue cancel
>
>Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
>Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
>---
> drivers/media/common/videobuf2/videobuf2-core.c | 197 ++++++++++++++++++++----
> drivers/media/common/videobuf2/videobuf2-v4l2.c |  34 +++-
> drivers/media/dvb-core/dvb_vb2.c                |   2 +-
> drivers/media/v4l2-core/Kconfig                 |  33 ++++
> include/media/videobuf2-core.h                  |  14 +-
> 5 files changed, 249 insertions(+), 31 deletions(-)
>
>diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>index 6b8e083893ad..996b99497a98 100644
>--- a/drivers/media/common/videobuf2/videobuf2-core.c
>+++ b/drivers/media/common/videobuf2/videobuf2-core.c
>@@ -352,6 +352,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
> 		vb->index = q->num_buffers + buffer;
> 		vb->type = q->type;
> 		vb->memory = memory;
>+		spin_lock_init(&vb->fence_cb_lock);
> 		for (plane = 0; plane < num_planes; ++plane) {
> 			vb->planes[plane].length = plane_sizes[plane];
> 			vb->planes[plane].min_length = plane_sizes[plane];
>@@ -905,20 +906,12 @@ void *vb2_plane_cookie(struct vb2_buffer *vb, unsigned int plane_no)
> }
> EXPORT_SYMBOL_GPL(vb2_plane_cookie);
>
>-void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>+static void vb2_process_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> {
> 	struct vb2_queue *q = vb->vb2_queue;
> 	unsigned long flags;
> 	unsigned int plane;
>
>-	if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
>-		return;
>-
>-	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
>-		    state != VB2_BUF_STATE_ERROR &&
>-		    state != VB2_BUF_STATE_QUEUED &&
>-		    state != VB2_BUF_STATE_REQUEUEING))
>-		state = VB2_BUF_STATE_ERROR;
>
> #ifdef CONFIG_VIDEO_ADV_DEBUG
> 	/*
>@@ -935,6 +928,9 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> 		call_void_memop(vb, finish, vb->planes[plane].mem_priv);
>
> 	spin_lock_irqsave(&q->done_lock, flags);
>+	if (vb->state == VB2_BUF_STATE_ACTIVE)
>+		atomic_dec(&q->owned_by_drv_count);
>+
> 	if (state == VB2_BUF_STATE_QUEUED ||
> 	    state == VB2_BUF_STATE_REQUEUEING) {
> 		vb->state = VB2_BUF_STATE_QUEUED;
>@@ -943,7 +939,7 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> 		list_add_tail(&vb->done_entry, &q->done_list);
> 		vb->state = state;
> 	}
>-	atomic_dec(&q->owned_by_drv_count);
>+
> 	spin_unlock_irqrestore(&q->done_lock, flags);
>
> 	trace_vb2_buf_done(q, vb);
>@@ -960,6 +956,36 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> 		wake_up(&q->done_wq);
> 		break;
> 	}
>+
>+}
>+
>+void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>+{
>+	if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
>+		return;
>+
>+	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
>+		    state != VB2_BUF_STATE_ERROR &&
>+		    state != VB2_BUF_STATE_QUEUED &&
>+		    state != VB2_BUF_STATE_REQUEUEING))
>+		state = VB2_BUF_STATE_ERROR;
>+
>+	vb2_process_buffer_done(vb, state);
>+
>+	/*
>+	 * Check if there is any buffer with error in the next position of the queue,
>+	 * buffers whose in-fence signaled with error are not queued to the driver
>+	 * and kept on the queue until the buffer before them is done, so to not
>+	 * deliver buffers back to userspace in the wrong order. Here we process
>+	 * any existing buffers with errors and wake up userspace.
>+	 */
>+	for (;;) {
>+		vb = list_next_entry(vb, queued_entry);
>+		if (!vb || vb->state != VB2_BUF_STATE_ERROR)
>+			break;
>+
>+		vb2_process_buffer_done(vb, VB2_BUF_STATE_ERROR);
>+        }
> }
> EXPORT_SYMBOL_GPL(vb2_buffer_done);
>
>@@ -1244,6 +1270,9 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
> {
> 	struct vb2_queue *q = vb->vb2_queue;
>
>+	if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
>+		return;

Seems like this is not needed now. Either __enqueue_in_driver() is
called when there's no in_fence; or it's called from the fence_cb in
which case we're guaranteed to already be signaled.

Might be worth a loud error if these conditions are ever true - but
the silent return is a leftover from old patches I think.

>+
> 	vb->state = VB2_BUF_STATE_ACTIVE;
> 	atomic_inc(&q->owned_by_drv_count);
>
>@@ -1295,6 +1324,24 @@ static int __buf_prepare(struct vb2_buffer *vb, const void *pb)
> 	return 0;
> }
>
>+static int __get_num_ready_buffers(struct vb2_queue *q)
>+{
>+	struct vb2_buffer *vb;
>+	int ready_count = 0;
>+	unsigned long flags;
>+
>+	/* count num of buffers ready in front of the queued_list */
>+	list_for_each_entry(vb, &q->queued_list, queued_entry) {
>+		spin_lock_irqsave(&vb->fence_cb_lock, flags);
>+		if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
>+			break;
>+		ready_count++;
>+		spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+	}
>+
>+	return ready_count;
>+}
>+
> int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
> {
> 	struct vb2_buffer *vb;
>@@ -1383,9 +1430,43 @@ static int vb2_start_streaming(struct vb2_queue *q)
> 	return ret;
> }
>
>-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
>+static void vb2_qbuf_fence_cb(struct dma_fence *f, struct dma_fence_cb *cb)
>+{
>+	struct vb2_buffer *vb = container_of(cb, struct vb2_buffer, fence_cb);
>+	struct vb2_queue *q = vb->vb2_queue;
>+	unsigned long flags;
>+
>+	spin_lock_irqsave(&vb->fence_cb_lock, flags);
>+	/*
>+	 * If the fence signals with an error we mark the buffer as such
>+	 * and avoid using it by setting it to VB2_BUF_STATE_ERROR and
>+	 * not queueing it to the driver. However we can't notify the error
>+	 * to userspace right now because, at the time this callback run, QBUF
>+	 * has returned already.
>+	 * So we delay that to DQBUF time. See comments in vb2_buffer_done()
>+	 * as well.
>+	 */
>+	if (vb->in_fence->error)
>+		vb->state = VB2_BUF_STATE_ERROR;
>+
>+	dma_fence_put(vb->in_fence);
>+	vb->in_fence = NULL;
>+
>+	if (vb->state == VB2_BUF_STATE_ERROR) {
>+		spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+		return;
>+	}
>+
>+	if (q->start_streaming_called)
>+		__enqueue_in_driver(vb);
>+	spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+}
>+
>+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
>+		  struct dma_fence *in_fence)
> {
> 	struct vb2_buffer *vb;
>+	unsigned long flags;
> 	int ret;
>
> 	vb = q->bufs[index];
>@@ -1394,16 +1475,18 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> 	case VB2_BUF_STATE_DEQUEUED:
> 		ret = __buf_prepare(vb, pb);
> 		if (ret)
>-			return ret;
>+			goto err;
> 		break;
> 	case VB2_BUF_STATE_PREPARED:
> 		break;
> 	case VB2_BUF_STATE_PREPARING:
> 		dprintk(1, "buffer still being prepared\n");
>-		return -EINVAL;
>+		ret = -EINVAL;
>+		goto err;
> 	default:
> 		dprintk(1, "invalid buffer state %d\n", vb->state);
>-		return -EINVAL;
>+		ret = -EINVAL;
>+		goto err;
> 	}
>
> 	/*
>@@ -1414,6 +1497,7 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> 	q->queued_count++;
> 	q->waiting_for_buffers = false;
> 	vb->state = VB2_BUF_STATE_QUEUED;
>+	vb->in_fence = in_fence;
>
> 	if (pb)
> 		call_void_bufop(q, copy_timestamp, vb, pb);
>@@ -1421,15 +1505,40 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> 	trace_vb2_qbuf(q, vb);
>
> 	/*
>-	 * If already streaming, give the buffer to driver for processing.
>-	 * If not, the buffer will be given to driver on next streamon.
>+	 * For explicit synchronization: If the fence didn't signal
>+	 * yet we setup a callback to queue the buffer once the fence
>+	 * signals and then return successfully. But if the fence
>+	 * already signaled we lose the reference we held and queue the
>+	 * buffer to the driver.
> 	 */
>-	if (q->start_streaming_called)
>-		__enqueue_in_driver(vb);
>+	spin_lock_irqsave(&vb->fence_cb_lock, flags);
>+	if (vb->in_fence) {
>+		ret = dma_fence_add_callback(vb->in_fence, &vb->fence_cb,
>+					     vb2_qbuf_fence_cb);
>+		/* is the fence signaled? */
>+		if (ret == -ENOENT) {
>+			dma_fence_put(vb->in_fence);
>+			vb->in_fence = NULL;
>+		} else if (ret) {
>+			goto unlock;
>+		}
>+	}
>
>-	/* Fill buffer information for the userspace */
>-	if (pb)
>-		call_void_bufop(q, fill_user_buffer, vb, pb);
>+	/*
>+	 * If already streaming and there is no fence to wait on
>+	 * give the buffer to driver for processing.
>+	 */
>+	if (q->start_streaming_called) {
>+		struct vb2_buffer *b;
>+
>+		list_for_each_entry(b, &q->queued_list, queued_entry) {
>+			if (b->state != VB2_BUF_STATE_QUEUED)
>+				continue;
>+			if (b->in_fence)
>+				break;
>+			__enqueue_in_driver(b);
>+		}
>+	}
>
> 	/*
> 	 * If streamon has been called, and we haven't yet called
>@@ -1438,14 +1547,36 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> 	 * then we can finally call start_streaming().
> 	 */
> 	if (q->streaming && !q->start_streaming_called &&
>-	    q->queued_count >= q->min_buffers_needed) {
>+	    __get_num_ready_buffers(q) >= q->min_buffers_needed) {
> 		ret = vb2_start_streaming(q);

If (q->streaming && !q->start_streaming_called), and all buffers have
in_fences which aren't signalled yet, then who calls
vb2_start_streaming()?

It seems like the fence path will always jump over here, and I don't
see a call to vb2_start_streaming() in the fence_cb path. (Sorry if I
missed something).

> 		if (ret)
>-			return ret;
>+			goto unlock;
> 	}
>
>+	spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+
>+	/* Fill buffer information for the userspace */
>+	if (pb)
>+		call_void_bufop(q, fill_user_buffer, vb, pb);
>+
> 	dprintk(2, "qbuf of buffer %d succeeded\n", vb->index);
> 	return 0;
>+
>+unlock:
>+	spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+
>+err:
>+	/* Fill buffer information for the userspace */
>+	if (pb)
>+		call_void_bufop(q, fill_user_buffer, vb, pb);
>+
>+	if (vb->in_fence) {
>+		dma_fence_put(vb->in_fence);
>+		vb->in_fence = NULL;
>+	}
>+
>+	return ret;
>+
> }
> EXPORT_SYMBOL_GPL(vb2_core_qbuf);
>
>@@ -1656,6 +1787,8 @@ EXPORT_SYMBOL_GPL(vb2_core_dqbuf);
> static void __vb2_queue_cancel(struct vb2_queue *q)
> {
> 	unsigned int i;
>+	struct vb2_buffer *vb;
>+	unsigned long flags;
>
> 	/*
> 	 * Tell driver to stop all transactions and release all queued
>@@ -1686,6 +1819,16 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
> 	q->queued_count = 0;
> 	q->error = 0;
>
>+	list_for_each_entry(vb, &q->queued_list, queued_entry) {
>+		spin_lock_irqsave(&vb->fence_cb_lock, flags);
>+		if (vb->in_fence) {
>+			dma_fence_remove_callback(vb->in_fence, &vb->fence_cb);
>+			dma_fence_put(vb->in_fence);
>+			vb->in_fence = NULL;
>+		}
>+		spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
>+	}
>+
> 	/*
> 	 * Remove all buffers from videobuf's list...
> 	 */
>@@ -1756,7 +1899,7 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type)
> 	 * Tell driver to start streaming provided sufficient buffers
> 	 * are available.
> 	 */
>-	if (q->queued_count >= q->min_buffers_needed) {
>+	if (__get_num_ready_buffers(q) >= q->min_buffers_needed) {
> 		ret = v4l_vb2q_enable_media_source(q);
> 		if (ret)
> 			return ret;
>@@ -2278,7 +2421,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
> 		 * Queue all buffers.
> 		 */
> 		for (i = 0; i < q->num_buffers; i++) {
>-			ret = vb2_core_qbuf(q, i, NULL);
>+			ret = vb2_core_qbuf(q, i, NULL, NULL);
> 			if (ret)
> 				goto err_reqbufs;
> 			fileio->bufs[i].queued = 1;
>@@ -2457,7 +2600,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
>
> 		if (copy_timestamp)
> 			b->timestamp = ktime_get_ns();
>-		ret = vb2_core_qbuf(q, index, NULL);
>+		ret = vb2_core_qbuf(q, index, NULL, NULL);
> 		dprintk(5, "vb2_dbuf result: %d\n", ret);
> 		if (ret)
> 			return ret;
>@@ -2560,7 +2703,7 @@ static int vb2_thread(void *data)
> 		if (copy_timestamp)
> 			vb->timestamp = ktime_get_ns();
> 		if (!threadio->stop)
>-			ret = vb2_core_qbuf(q, vb->index, NULL);
>+			ret = vb2_core_qbuf(q, vb->index, NULL, NULL);
> 		call_void_qop(q, wait_prepare, q);
> 		if (ret || threadio->stop)
> 			break;
>diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>index b1c0fa2b0b88..74d7062e5285 100644
>--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
>+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>@@ -23,6 +23,7 @@
> #include <linux/sched.h>
> #include <linux/freezer.h>
> #include <linux/kthread.h>
>+#include <linux/sync_file.h>
>
> #include <media/v4l2-dev.h>
> #include <media/v4l2-fh.h>
>@@ -178,6 +179,17 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b,
> 		return -EINVAL;
> 	}
>
>+	if ((b->fence_fd != 0 && b->fence_fd != -1) &&
>+	    !(b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
>+		dprintk(1, "%s: fence_fd set without IN_FENCE flag\n", opname);
>+		return -EINVAL;
>+	}
>+
>+	if (b->fence_fd < 0 && (b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
>+		dprintk(1, "%s: IN_FENCE flag set but no fence_fd\n", opname);
>+		return -EINVAL;
>+	}
>+
> 	return __verify_planes_array(q->bufs[b->index], b);
> }
>
>@@ -203,9 +215,14 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
> 	b->timestamp = ns_to_timeval(vb->timestamp);
> 	b->timecode = vbuf->timecode;
> 	b->sequence = vbuf->sequence;
>-	b->fence_fd = 0;
> 	b->reserved = 0;
>
>+	b->fence_fd = 0;

I didn't understand why we're returning 0 instead of -1. Actually the
doc in patch 10 seems to say it will be -1 or 0 depending on whether
we set one of the fence flags? I'm not sure:

    For all other ioctls V4L2 sets this field to -1 if
    ``V4L2_BUF_FLAG_IN_FENCE`` and/or ``V4L2_BUF_FLAG_OUT_FENCE`` are set,
    otherwise this field is set to 0 for backward compatibility.

Cheers,
-Brian

>+	if (vb->in_fence)
>+		b->flags |= V4L2_BUF_FLAG_IN_FENCE;
>+	else
>+		b->flags &= ~V4L2_BUF_FLAG_IN_FENCE;
>+
> 	if (q->is_multiplanar) {
> 		/*
> 		 * Fill in plane-related data if userspace provided an array
>@@ -562,6 +579,7 @@ EXPORT_SYMBOL_GPL(vb2_create_bufs);
>
> int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
> {
>+	struct dma_fence *in_fence = NULL;
> 	int ret;
>
> 	if (vb2_fileio_is_active(q)) {
>@@ -570,7 +588,19 @@ int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
> 	}
>
> 	ret = vb2_queue_or_prepare_buf(q, b, "qbuf");
>-	return ret ? ret : vb2_core_qbuf(q, b->index, b);
>+	if (ret)
>+		return ret;
>+
>+	if (b->flags & V4L2_BUF_FLAG_IN_FENCE) {
>+		in_fence = sync_file_get_fence(b->fence_fd);
>+		if (!in_fence) {
>+			dprintk(1, "failed to get in-fence from fd %d\n",
>+				b->fence_fd);
>+			return -EINVAL;
>+		}
>+	}
>+
>+	return vb2_core_qbuf(q, b->index, b, in_fence);
> }
> EXPORT_SYMBOL_GPL(vb2_qbuf);
>
>diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
>index b811adf88afa..7da53f10db1a 100644
>--- a/drivers/media/dvb-core/dvb_vb2.c
>+++ b/drivers/media/dvb-core/dvb_vb2.c
>@@ -385,7 +385,7 @@ int dvb_vb2_qbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
> {
> 	int ret;
>
>-	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b);
>+	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b, NULL);
> 	if (ret) {
> 		dprintk(1, "[%s] index=%d errno=%d\n", ctx->name,
> 			b->index, ret);
>diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
>index 8e37e7c5e0f7..79dfb5dfd1fc 100644
>--- a/drivers/media/v4l2-core/Kconfig
>+++ b/drivers/media/v4l2-core/Kconfig
>@@ -80,3 +80,36 @@ config VIDEOBUF_DMA_CONTIG
> config VIDEOBUF_DVB
> 	tristate
> 	select VIDEOBUF_GEN
>+
>+# Used by drivers that need Videobuf2 modules
>+config VIDEOBUF2_CORE
>+	select DMA_SHARED_BUFFER
>+	select SYNC_FILE
>+	tristate
>+
>+config VIDEOBUF2_MEMOPS
>+	tristate
>+	select FRAME_VECTOR
>+
>+config VIDEOBUF2_DMA_CONTIG
>+	tristate
>+	depends on HAS_DMA
>+	select VIDEOBUF2_CORE
>+	select VIDEOBUF2_MEMOPS
>+	select DMA_SHARED_BUFFER
>+
>+config VIDEOBUF2_VMALLOC
>+	tristate
>+	select VIDEOBUF2_CORE
>+	select VIDEOBUF2_MEMOPS
>+	select DMA_SHARED_BUFFER
>+
>+config VIDEOBUF2_DMA_SG
>+	tristate
>+	depends on HAS_DMA
>+	select VIDEOBUF2_CORE
>+	select VIDEOBUF2_MEMOPS
>+
>+config VIDEOBUF2_DVB
>+	tristate
>+	select VIDEOBUF2_CORE
>diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>index 364e4cb41b10..28ce8f66882e 100644
>--- a/include/media/videobuf2-core.h
>+++ b/include/media/videobuf2-core.h
>@@ -17,6 +17,7 @@
> #include <linux/poll.h>
> #include <linux/dma-buf.h>
> #include <linux/bitops.h>
>+#include <linux/dma-fence.h>
>
> #define VB2_MAX_FRAME	(32)
> #define VB2_MAX_PLANES	(8)
>@@ -255,12 +256,21 @@ struct vb2_buffer {
> 	 * done_entry:		entry on the list that stores all buffers ready
> 	 *			to be dequeued to userspace
> 	 * vb2_plane:		per-plane information; do not change
>+	 * in_fence:		fence received from vb2 client to wait on before
>+	 *			using the buffer (queueing to the driver)
>+	 * fence_cb:		fence callback information
>+	 * fence_cb_lock:	protect callback signal/remove
> 	 */
> 	enum vb2_buffer_state	state;
>
> 	struct vb2_plane	planes[VB2_MAX_PLANES];
> 	struct list_head	queued_entry;
> 	struct list_head	done_entry;
>+
>+	struct dma_fence	*in_fence;
>+	struct dma_fence_cb	fence_cb;
>+	spinlock_t              fence_cb_lock;
>+
> #ifdef CONFIG_VIDEO_ADV_DEBUG
> 	/*
> 	 * Counters for how often these buffer-related ops are
>@@ -773,6 +783,7 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
>  * @index:	id number of the buffer
>  * @pb:		buffer structure passed from userspace to
>  *		v4l2_ioctl_ops->vidioc_qbuf handler in driver
>+ * @in_fence:	in-fence to wait on before queueing the buffer
>  *
>  * Videobuf2 core helper to implement VIDIOC_QBUF() operation. It is called
>  * internally by VB2 by an API-specific handler, like ``videobuf2-v4l2.h``.
>@@ -787,7 +798,8 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
>  *
>  * Return: returns zero on success; an error code otherwise.
>  */
>-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb);
>+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
>+		  struct dma_fence *in_fence);
>
> /**
>  * vb2_core_dqbuf() - Dequeue a buffer to the userspace
>-- 
>2.16.3
>

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