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    SubjectRe: [PATCH v9 2/9] media: v4l: Add definitions for MPEG-2 slice format and metadata
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    On 09/07/2018 12:24 AM, Paul Kocialkowski wrote:
    > From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
    >
    > Stateless video decoding engines require both the MPEG-2 slices and
    > associated metadata from the video stream in order to decode frames.
    >
    > This introduces definitions for a new pixel format, describing buffers
    > with MPEG-2 slice data, as well as control structure sfor passing the
    > frame metadata to drivers.
    >
    > This is based on work from both Florent Revest and Hugues Fruchet.
    >
    > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
    > ---
    > .../media/uapi/v4l/extended-controls.rst | 176 ++++++++++++++++++
    > .../media/uapi/v4l/pixfmt-compressed.rst | 16 ++
    > .../media/uapi/v4l/vidioc-queryctrl.rst | 14 +-
    > .../media/videodev2.h.rst.exceptions | 2 +
    > drivers/media/v4l2-core/v4l2-ctrls.c | 63 +++++++
    > drivers/media/v4l2-core/v4l2-ioctl.c | 1 +
    > include/media/v4l2-ctrls.h | 18 +-
    > include/uapi/linux/v4l2-controls.h | 65 +++++++
    > include/uapi/linux/videodev2.h | 5 +
    > 9 files changed, 351 insertions(+), 9 deletions(-)
    >
    > diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
    > index 9f7312bf3365..f1951236266a 100644
    > --- a/Documentation/media/uapi/v4l/extended-controls.rst
    > +++ b/Documentation/media/uapi/v4l/extended-controls.rst
    > @@ -1497,6 +1497,182 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
    >
    >
    >
    > +.. _v4l2-mpeg-mpeg2:
    > +
    > +``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
    > + Specifies the slice parameters (as extracted from the bitstream) for the
    > + associated MPEG-2 slice data. This includes the necessary parameters for
    > + configuring a stateless hardware decoding pipeline for MPEG-2.
    > + The bitstream parameters are defined according to :ref:`mpeg2part2`.
    > +
    > +.. c:type:: v4l2_ctrl_mpeg2_slice_params
    > +
    > +.. cssclass:: longtable
    > +
    > +.. flat-table:: struct v4l2_ctrl_mpeg2_slice_params
    > + :header-rows: 0
    > + :stub-columns: 0
    > + :widths: 1 1 2
    > +
    > + * - __u32
    > + - ``bit_size``
    > + - Size (in bits) of the current slice data.
    > + * - __u32
    > + - ``data_bit_offset``
    > + - Offset (in bits) to the video data in the current slice data.
    > + * - struct :c:type:`v4l2_mpeg2_sequence`
    > + - ``sequence``
    > + - Structure with MPEG-2 sequence metadata, merging relevant fields from
    > + the sequence header and sequence extension parts of the bitstream.
    > + * - struct :c:type:`v4l2_mpeg2_picture`
    > + - ``picture``
    > + - Structure with MPEG-2 picture metadata, merging relevant fields from
    > + the picture header and picture coding extension parts of the bitstream.
    > + * - __u8
    > + - ``quantiser_scale_code``
    > + - Code used to determine the quantization scale to use for the IDCT.
    > + * - __u8
    > + - ``backward_ref_index``
    > + - Index for the V4L2 buffer to use as backward reference, used with
    > + B-coded and P-coded frames.
    > + * - __u8
    > + - ``forward_ref_index``
    > + - Index for the V4L2 buffer to use as forward reference, used with
    > + P-coded frames.

    Do these indices refer to the output or capture buffers? I think these should
    refer to the output buffers, since this control is used in a request for the
    output side.

    Regards,

    Hans

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