[RFC][PATCH 13/15] videobuf2: do not sync buffers for DMABUF queues

[Sergey Senozhatsky]

DMA-exporter is supposed to handle cache syncs, so we can
avoid ->prepare()/->finish() syncs from videobuf2 core for
DMABUF buffers.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/media/common/videobuf2/videobuf2-v4l2.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 1762849288ae..2b9d3318e6fb 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -341,8 +341,22 @@ static void set_buffer_cache_hints(struct vb2_queue *q,
 				   struct vb2_buffer *vb,
 				   struct v4l2_buffer *b)
 {
-	vb->need_cache_sync_on_prepare = 1;
+	/*
+	 * DMA exporter should take care of cache syncs, so we can avoid
+	 * explicit ->prepare()/->finish() syncs.
+	 */
+	if (q->memory == VB2_MEMORY_DMABUF) {
+		vb->need_cache_sync_on_finish = 0;
+		vb->need_cache_sync_on_prepare = 0;
+		return;
+	}
 
+	/*
+	 * For other ->memory types we always need ->prepare() cache
+	 * sync. ->finish() cache sync, however, can be avoided when queue
+	 * direction is TO_DEVICE.
+	 */
+	vb->need_cache_sync_on_prepare = 1;
 	if (q->dma_dir != DMA_TO_DEVICE)
 		vb->need_cache_sync_on_finish = 1;
 	else
-- 
2.24.1.735.g03f4e72817-goog