Re: [PATCH v9 11/15] vb2: add in-fence support to QBUF

[Hans Verkuil]

On 05/09/18 12:36, Brian Starkey wrote:
> Hi Ezequiel,
> 
> On Fri, May 04, 2018 at 05:06:08PM -0300, Ezequiel Garcia wrote:
>> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxx>
>> Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
>> ---
>> 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).

Good point, I think you are right about that.

This same sequence should be present in the fence_cb path. Question: can
fence_cb be called from interrupt context? If so, then that needs to start a
workqueue or something since vb2_start_streaming cannot run in interrupt
context. And in addition that workqueue needs to take and release q->lock.
We should discuss locking on irc, there are some subtleties there.

This would be a good test to add to v4l2-compliance, BTW.

> 
>> 		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.

I'm not sure about this either. This also ties in with the Request API
series which has a similar issue. I think setting this to -1 when unused
is better.

Regards,

	Hans

> 
> 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
>>