Date:   Fri, 12 Jan 2018 14:46:07 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Gustavo Padovan <gustavo@...ovan.org>, linux-media@...r.kernel.org
Cc:     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>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v7 4/6] [media] vb2: add in-fence support to QBUF

On 01/10/18 17:07, Gustavo Padovan 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 queue to the driver
> out of the order they were queued from userspace. That means that even if
> it fence signal it must wait 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.
> 
> 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>
> ---
>  drivers/media/common/videobuf/videobuf2-core.c | 166 ++++++++++++++++++++++---
>  drivers/media/common/videobuf/videobuf2-v4l2.c |  29 ++++-
>  drivers/media/v4l2-core/Kconfig                |  33 +++++
>  include/media/videobuf2-core.h                 |  14 ++-
>  4 files changed, 221 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf/videobuf2-core.c b/drivers/media/common/videobuf/videobuf2-core.c
> index f7109f827f6e..777e3a2bc746 100644
> --- a/drivers/media/common/videobuf/videobuf2-core.c
> +++ b/drivers/media/common/videobuf/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];
> @@ -936,7 +937,7 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>  
>  	switch (state) {
>  	case VB2_BUF_STATE_QUEUED:
> -		return;
> +		break;
>  	case VB2_BUF_STATE_REQUEUEING:
>  		if (q->start_streaming_called)
>  			__enqueue_in_driver(vb);
> @@ -946,6 +947,19 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>  		wake_up(&q->done_wq);
>  		break;
>  	}
> +
> +	/*
> +	 * The check below verifies if there is a buffer in queue with an

s/in/in the/

> +	 * error state. They are added to queue in the error state when
> +	 * their in-fence fails to signal.
> +	 * To not mess with buffer ordering we wait until the previous buffer
> +	 * is done to mark the buffer in the error state as done and notify
> +	 * userspace. So everytime a buffer is done we check the next one for

s/everytime/every time/

> +	 * VB2_BUF_STATE_ERROR.
> +	 */
> +	vb = list_next_entry(vb, queued_entry);
> +	if (vb && vb->state == VB2_BUF_STATE_ERROR)
> +		vb2_buffer_done(vb, vb->state);

Hmm. I'm not sure this is correct. Please test this and make sure you have
enabled CONFIG_VIDEO_ADV_DEBUG. This enables additional instrumentation that
will warn if the internal vb2 state becomes unbalanced.

An additional problem I have with this recursive call is what happens when
a whole bunch of in fences signal an error, so you have e.g. 10 consecutive
buffers with state ERROR. You'd recurse 10 times in that case.

I think you are better off handling this corner case explicitly, e.g. something
like this:

	for (;;) {
		vb = list_next_entry(vb, queued_entry);
		if (!vb || vb->state != VB2_BUF_STATE_ERROR)
			break;

	        dprintk(4, "done processing on buffer %d, state: %d\n",
        	        vb->index, vb->state);

		if (state == VB2_BUF_STATE_QUEUED) {
			vb->state = state;
		} else {
		        spin_lock_irqsave(&q->done_lock, flags);
                	/* Add the buffer to the done buffers list */
        	        list_add_tail(&vb->done_entry, &q->done_list);
		        spin_unlock_irqrestore(&q->done_lock, flags);

	                /* Inform any processes that may be waiting for buffers */
        	        wake_up(&q->done_wq);
		}

        	trace_vb2_buf_done(q, vb);
	}

I *think* this ensures all counters remain balanced, but this really needs
to be tested. I haven't compiled this code, so I hope I got it right.

>  }
>  EXPORT_SYMBOL_GPL(vb2_buffer_done);
>  
> @@ -1230,6 +1244,9 @@ 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;
> +
>  	vb->state = VB2_BUF_STATE_ACTIVE;
>  	atomic_inc(&q->owned_by_drv_count);
>  
> @@ -1281,6 +1298,24 @@ 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;
> @@ -1369,9 +1404,43 @@ 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 signal with an error we mark the buffer as such

s/signal/signals/

> +	 * 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
> +	 * 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 *fence)
>  {
>  	struct vb2_buffer *vb;
> +	unsigned long flags;
>  	int ret;
>  
>  	vb = q->bufs[index];
> @@ -1380,16 +1449,18 @@ 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;
>  	}
>  
>  	/*
> @@ -1400,6 +1471,7 @@ 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 = fence;
>  
>  	if (pb)
>  		call_void_bufop(q, copy_timestamp, vb, pb);
> @@ -1407,15 +1479,42 @@ 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);
> +		if (ret == -EINVAL) {
> +			spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> +			goto err;
> +		} else if (!ret) {
> +			goto fill;
> +		}
>  
> -	/* Fill buffer information for the userspace */
> -	if (pb)
> -		call_void_bufop(q, fill_user_buffer, vb, pb);
> +		dma_fence_put(vb->in_fence);
> +		vb->in_fence = NULL;
> +	}
> +
> +fill:
> +	/*
> +	 * 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;

Add empty line.

> +		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
> @@ -1424,14 +1523,33 @@ 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 (ret)
> -			return ret;
> +			goto err;

You're missing a spin_unlock_irqrestore() call in this error path.

>  	}
>  
> +	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;
> +
> +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);
>  
> @@ -1642,6 +1760,8 @@ 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
> @@ -1672,6 +1792,16 @@ 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...
>  	 */
> @@ -1733,7 +1863,7 @@ 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;
> @@ -2255,7 +2385,7 @@ 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;
> @@ -2434,7 +2564,7 @@ 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;
> @@ -2537,7 +2667,7 @@ 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/videobuf/videobuf2-v4l2.c b/drivers/media/common/videobuf/videobuf2-v4l2.c
> index d838524a459e..0a41e3bb7733 100644
> --- a/drivers/media/common/videobuf/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf/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 +179,12 @@ 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) &&

Wouldn't 'b->fence_fd > 0' be more sensible?

And possibly just set fence_fd to 0 if it is < 0.

> +	    !(b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
> +		dprintk(1, "%s: fence_fd set without IN_FENCE flag\n", opname);
> +		return -EINVAL;
> +	}
> +
>  	return __verify_planes_array(q->bufs[b->index], b);
>  }
>  
> @@ -203,9 +210,14 @@ 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;
> +	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 +574,7 @@ EXPORT_SYMBOL_GPL(vb2_create_bufs);
>  
>  int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
>  {
> +	struct dma_fence *fence = NULL;
>  	int ret;
>  
>  	if (vb2_fileio_is_active(q)) {
> @@ -570,7 +583,19 @@ 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) {
> +		fence = sync_file_get_fence(b->fence_fd);
> +		if (!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, fence);
>  }
>  EXPORT_SYMBOL_GPL(vb2_qbuf);
>  
> diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
> index bf52fbd07aed..a39968eb1d32 100644
> --- a/drivers/media/v4l2-core/Kconfig
> +++ b/drivers/media/v4l2-core/Kconfig
> @@ -79,3 +79,36 @@ 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 583cdc06de79..0a2b1ac12dd0 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 receive from vb2 client to wait on before

receive -> received

> +	 *			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
> @@ -750,6 +760,7 @@ 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
> + * @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``.
> @@ -764,7 +775,8 @@ 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 *fence);
>  
>  /**
>   * vb2_core_dqbuf() - Dequeue a buffer to the userspace
> 

Regards,

	Hans

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