Hi Dmitry,
thanks for giving a second look a this issue.
Le mardi 22 mars 2022 à 16:23 +0300, Dmitry Osipenko a écrit :
> Use data offsets provided by applications for multi-planar capture
> buffers. This allows V4L to import and use dma-bufs exported by other
> subsystems in cases where application wants to customize data offsets
> of capture buffers in order to meet hardware alignment requirements of
> both dma-buf exporter and importer.
>
> This feature is wanted for providing a better support of media hardware
> found on Chromebooks. In particular display and camera ISP hardware of
> Rockchip and MediaTek SoCs require special handling by userspace because
> display h/w has specific alignment requirements that don't match default
> alignments expected by V4L and there is a need to customize the data
> offsets in case of multi-planar formats.
>
> Some drivers already have preliminary support for data offsets
> customization of capture buffers, like NVIDIA Tegra video decoder driver
> for example, and V4L allows applications to provide data offsets for
> multi-planar output buffers, let's support such customization for the
> capture buffers as well.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> ---
> Documentation/userspace-api/media/v4l/buffer.rst | 9 ++++++++-
> drivers/media/common/videobuf2/videobuf2-v4l2.c | 7 +++++++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst
> index 4638ec64db00..75b1929e2acb 100644
> --- a/Documentation/userspace-api/media/v4l/buffer.rst
> +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> @@ -369,13 +369,20 @@ struct v4l2_plane
> - ``data_offset``
> - Offset in bytes to video data in the plane. Drivers must set this
> field when ``type`` refers to a capture stream, applications when
> - it refers to an output stream.
> + it refers to an output or capture stream.
There is a clear contradiction in this paragraph. Both the driver and the
application MUST set the data_offset.
Would it be possible to demo your idea by implementing this in a virtual driver
? vivid already have data_offset for capture in some cases, you could verify if
your idea works without any conflict in this scenario.
>
> .. note::
>
> That data_offset is included in ``bytesused``. So the
> size of the image in the plane is ``bytesused``-``data_offset``
> at offset ``data_offset`` from the start of the plane.
> +
> + For capture planes data_offset may be specified by applications
> + and by drivers. Driver may override application's offset or error
> + out buffer if offset can't be satisfied by hardware. This allows
> + applications to customize data offsets of imported dma-bufs.
> + Handling of application's offsets is driver-dependent, application
> + must use the resulting buffer offset.
> * - __u32
> - ``reserved[11]``
> - Reserved for future use. Should be zeroed by drivers and
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 6edf4508c636..929107a431cc 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -263,6 +263,13 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
> psrc->bytesused : pdst->length;
> pdst->data_offset = psrc->data_offset;
> }
> + } else {
> + for (plane = 0; plane < vb->num_planes; ++plane) {
> + struct vb2_plane *pdst = &planes[plane];
> + struct v4l2_plane *psrc = &b->m.planes[plane];
> +
> + pdst->data_offset = psrc->data_offset;
> + }
> }
> } else {
> /*
