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

Hans Verkuil
2018-05-07T12:07:12Z

On 04/05/18 22:06, Ezequiel Garcia wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.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@collabora.com>
> Signed-off-by: Ezequiel Garcia <ezequiel@collabora.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 (;;) {

I think this should test if the list is empty before calling list_next_entry().

> + vb = list_next_entry(vb, queued_entry);
> + if (!vb || vb->state != VB2_BUF_STATE_ERROR)

The !vb check makes no sense. list_next_entry won't return NULL if there is no
next entry, you need to call list_empty() first.

> + 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;
> +
> 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)

I'd change this to:

if (q->start_streaming_called &&
vb->state != VB2_BUF_STATE_ERROR)

Then you can drop the previous 'if'.

> + __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.

What happens if the fence signaled an error? Is that error returned to userspace?
(i.e. VIDIOC_QBUF will fail in that case)

> */
> - 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 (ret)
> - return ret;
> + goto unlock;
> }
>
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> +
> + /* Fill buffer information for the userspace */

s/the//

> + 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 */

s/the//

> + 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;
> + 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

This chunk doesn't really belong here. Should be a separate patch with an explanation
why.

> 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;
> +

So for the _MPLANE formats this is one fence for all planes. Which makes sense, but how
does drm handle that? Also one fence for all planes?

I think there should be a comment about this somewhere.

> #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
>

Regards,

Hans