Hi Laurent, On 10/9/22 23:35, Laurent Pinchart wrote: > From: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > > The V4L2 API historically allowed buffers to be queued with bytesused > set to 0 on output devices, in which case the driver would use the > buffer length. This behaviour is deprecated, and videobuf2 prints a > warning message in the kernel log. Drop it from the documentation. > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> Regards, Hans > --- > > This patch aims at starting (or continuing) the discussion related to > handling of bytesused == 0 on video output devices. videobuf2 currently > printes a warning that indicates the behaviour is deprecated, but the > API documentation allows it explicitly. This discrepency bothers me and > I think we should fix it. > > We probably won't be able to drop support for the deprecated behaviour > in the near future, if ever. If we want to push applications to get > fixed, we may want to replace the dev_warn() with a WARN_ONCE(), which > could be done in a v2 of this patch, or in another patch. > > Another option would be to consider that the behaviour is fine and keep > official support for it in the documentation, in which case vb2 should > stop warning about it. This wouldn't be my preference. > > --- > Documentation/userspace-api/media/v4l/buffer.rst | 11 +++-------- > 1 file changed, 3 insertions(+), 8 deletions(-) > > diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst > index 4638ec64db00..04dec3e570ed 100644 > --- a/Documentation/userspace-api/media/v4l/buffer.rst > +++ b/Documentation/userspace-api/media/v4l/buffer.rst > @@ -187,10 +187,8 @@ struct v4l2_buffer > on the negotiated data format and may change with each buffer for > compressed variable size data like JPEG images. Drivers must set > this field when ``type`` refers to a capture stream, applications > - when it refers to an output stream. If the application sets this > - to 0 for an output stream, then ``bytesused`` will be set to the > - size of the buffer (see the ``length`` field of this struct) by > - the driver. For multiplanar formats this field is ignored and the > + when it refers to an output stream. For multiplanar formats this field > + is ignored and the > ``planes`` pointer is used instead. > * - __u32 > - ``flags`` > @@ -327,10 +325,7 @@ struct v4l2_plane > - ``bytesused`` > - The number of bytes occupied by data in the plane (its payload). > Drivers must set this field when ``type`` refers to a capture > - stream, applications when it refers to an output stream. If the > - application sets this to 0 for an output stream, then > - ``bytesused`` will be set to the size of the plane (see the > - ``length`` field of this struct) by the driver. > + stream, applications when it refers to an output stream. > > .. note:: >
