On 2/4/20 3:56 AM, Sergey Senozhatsky wrote:
> Set video buffer cache management flags corresponding to V4L2 cache
> flags.
>
> Both ->prepare() and ->finish() cache management hints should be
> passed during this stage (buffer preparation), because there is no
> other way for user-space to skip ->finish() cache flush.
>
> There are two possible alternative approaches:
> - The first one is to move cache sync from ->finish() to dqbuf().
> But this breaks some drivers, that need to fix-up buffers before
> dequeueing them.
>
> - The second one is to move ->finish() call from ->done() to dqbuf.
>
> Change-Id: I3bef1d1fb93a5fba290ce760eaeecdc8e7d6885a
> Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> ---
> .../media/common/videobuf2/videobuf2-v4l2.c | 36 +++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index eb5d5db96552..2da06a2ad6c4 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -337,6 +337,41 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
> return 0;
> }
>
> +static void set_buffer_cache_hints(struct vb2_queue *q,
> + struct vb2_buffer *vb,
> + struct v4l2_buffer *b)
> +{
> + /*
> + * DMA exporter should take care of cache syncs, so we can avoid
> + * explicit ->prepare()/->finish() syncs. For other ->memory types
> + * we always need ->prepare() or/and ->finish() cache sync.
> + */
> + if (q->memory == VB2_MEMORY_DMABUF) {
> + vb->need_cache_sync_on_finish = 0;
> + vb->need_cache_sync_on_prepare = 0;
> + return;
> + }
> +
> + if (!q->allow_cache_hints)
> + return;
> +
> + vb->need_cache_sync_on_prepare = 1;
This needs a comment explaining why prepare is set to 1 by default. I remember
we discussed this earlier, and the conclusion of that discussion needs to be
documented here in a comment.
Regards,
Hans
> + /*
> + * ->finish() cache sync can be avoided when queue direction is
> + * TO_DEVICE.
> + */
> + if (q->dma_dir != DMA_TO_DEVICE)
> + vb->need_cache_sync_on_finish = 1;
> + else
> + vb->need_cache_sync_on_finish = 0;
> +
> + if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
> + vb->need_cache_sync_on_finish = 0;
> +
> + if (b->flags & V4L2_BUF_FLAG_NO_CACHE_CLEAN)
> + vb->need_cache_sync_on_prepare = 0;
> +}
> +
> static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
> struct v4l2_buffer *b, bool is_prepare,
> struct media_request **p_req)
> @@ -381,6 +416,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
> }
>
> if (!vb->prepared) {
> + set_buffer_cache_hints(q, vb, b);
> /* Copy relevant information provided by the userspace */
> memset(vbuf->planes, 0,
> sizeof(vbuf->planes[0]) * vb->num_planes);
>
