[libcamera-devel] [PATCH 1/4] libcamera: v4l2_videodevice: Ensure non-zero bytesused for output buffers

[Laurent Pinchart]

The V4L2 API specification indicates that, for an output video device,
the driver will interpret a zero bytesused value as the buffer length
(for v4l2_buffer) or the plane length (for v4l2_plane). The videobuf2
framework implements this behaviour, but also considers this case as
deprecated and prints a warning:

[   54.375534] use of bytesused == 0 is deprecated and will be removed in the future,
[   54.388026] use the actual size instead.

Avoid the warning by setting bytesused to the buffer or plane length
before queuing a buffer to an output video device.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/libcamera/v4l2_videodevice.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 955e150867ef..1dbb839ed456 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -1645,10 +1645,10 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
 			}
 
 			if (multiPlanar) {
-				v4l2Planes[0].bytesused = bytesused;
+				v4l2Planes[0].bytesused = bytesused ? : length;
 				v4l2Planes[0].length = length;
 			} else {
-				buf.bytesused = bytesused;
+				buf.bytesused = bytesused ? : length;
 				buf.length = length;
 			}
 		} else if (multiPlanar) {
@@ -1658,7 +1658,8 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
 			 * V4L2 buffer is guaranteed to be equal at this point.
 			 */
 			for (auto [i, plane] : utils::enumerate(planes)) {
-				v4l2Planes[i].bytesused = metadata.planes()[i].bytesused;
+				v4l2Planes[i].bytesused = metadata.planes()[i].bytesused
+							? : plane.length;
 				v4l2Planes[i].length = plane.length;
 			}
 		} else {
@@ -1666,7 +1667,8 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
 			 * Single-planar API with a single plane in the buffer
 			 * is trivial to handle.
 			 */
-			buf.bytesused = metadata.planes()[0].bytesused;
+			buf.bytesused = metadata.planes()[0].bytesused
+				      ? : planes[0].length;
 			buf.length = planes[0].length;
 		}
 
-- 
Regards,

Laurent Pinchart