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SubjectRe: [PATCH RESEND v7 1/2] media: uapi: Add H264 low-level decoder API compound controls.
Hi,

On Thu, Apr 4, 2019 at 9:26 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> From: Pawel Osciak <posciak@chromium.org>
>
> Stateless video codecs will require both the H264 metadata and slices in
> order to be able to decode frames.
>
> This introduces the definitions for a new pixel format for H264 slices that
> have been parsed, as well as the structures used to pass the metadata from
> the userspace to the kernel.
>
> Reviewed-by: Tomasz Figa <tfiga@chromium.org>
> Signed-off-by: Pawel Osciak <posciak@chromium.org>
> Signed-off-by: Guenter Roeck <groeck@chromium.org>
> Co-developed-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> ---
> Documentation/media/uapi/v4l/biblio.rst | 9 +-
> Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 569 ++++++++++++++-
> Documentation/media/uapi/v4l/pixfmt-compressed.rst | 19 +-
> Documentation/media/uapi/v4l/vidioc-queryctrl.rst | 30 +-
> Documentation/media/videodev2.h.rst.exceptions | 5 +-
> drivers/media/v4l2-core/v4l2-ctrls.c | 42 +-
> drivers/media/v4l2-core/v4l2-ioctl.c | 1 +-
> include/media/h264-ctrls.h | 192 +++++-
> include/media/v4l2-ctrls.h | 13 +-
> include/uapi/linux/videodev2.h | 1 +-
> 10 files changed, 880 insertions(+), 1 deletion(-)
> create mode 100644 include/media/h264-ctrls.h
>
> diff --git a/Documentation/media/uapi/v4l/biblio.rst b/Documentation/media/uapi/v4l/biblio.rst
> index ec33768c055e..8f4eb8823d82 100644
> --- a/Documentation/media/uapi/v4l/biblio.rst
> +++ b/Documentation/media/uapi/v4l/biblio.rst
> @@ -122,6 +122,15 @@ ITU BT.1119
>
> :author: International Telecommunication Union (http://www.itu.ch)
>
> +.. _h264:
> +
> +ITU-T Rec. H.264 Specification (04/2017 Edition)
> +================================================
> +
> +:title: ITU-T Recommendation H.264 "Advanced Video Coding for Generic Audiovisual Services"
> +
> +:author: International Telecommunication Union (http://www.itu.ch)
> +
> .. _jfif:
>
> JFIF
> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> index 67a122339c0e..1285bfec7d3d 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -1371,6 +1371,575 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> - Layer number
>
>
> +.. _v4l2-mpeg-h264:
> +
> +``V4L2_CID_MPEG_VIDEO_H264_SPS (struct)``
> + Specifies the sequence parameter set (as extracted from the
> + bitstream) for the associated H264 slice data. This includes the
> + necessary parameters for configuring a stateless hardware decoding
> + pipeline for H264. The bitstream parameters are defined according
> + to :ref:`h264`, section 7.4.2.1.1 "Sequence Parameter Set Data
> + Semantics". For further documentation, refer to the above
> + specification, unless there is an explicit comment stating
> + otherwise.
> +
> + .. note::
> +
> + This compound control is not yet part of the public kernel API and
> + it is expected to change.
> +
> +.. c:type:: v4l2_ctrl_h264_sps
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_ctrl_h264_sps
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - __u8
> + - ``profile_idc``
> + -
> + * - __u8
> + - ``constraint_set_flags``
> + - See :ref:`Sequence Parameter Set Constraints Set Flags <h264_sps_constraints_set_flags>`
> + * - __u8
> + - ``level_idc``
> + -
> + * - __u8
> + - ``seq_parameter_set_id``
> + -
> + * - __u8
> + - ``chroma_format_idc``
> + -
> + * - __u8
> + - ``bit_depth_luma_minus8``
> + -
> + * - __u8
> + - ``bit_depth_chroma_minus8``
> + -
> + * - __u8
> + - ``log2_max_frame_num_minus4``
> + -
> + * - __u8
> + - ``pic_order_cnt_type``
> + -
> + * - __u8
> + - ``log2_max_pic_order_cnt_lsb_minus4``
> + -
> + * - __u8
> + - ``max_num_ref_frames``
> + -
> + * - __u8
> + - ``num_ref_frames_in_pic_order_cnt_cycle``
> + -
> + * - __s32
> + - ``offset_for_ref_frame[255]``
> + -
> + * - __s32
> + - ``offset_for_non_ref_pic``
> + -
> + * - __s32
> + - ``offset_for_top_to_bottom_field``
> + -
> + * - __u16
> + - ``pic_width_in_mbs_minus1``
> + -
> + * - __u16
> + - ``pic_height_in_map_units_minus1``
> + -

We recently had some reflection with Alex that this is redundant with
the width and height in the OUTPUT format. It may also apply to some
other fields in these structs. I feel like they should be removed and
passed via corresponding generic V4L2 properties - format, selection,
etc.

The same problem is also present in the MPEG2 controls. In fact, there
was a patch already which used some fields from the controls to
calculate the destination buffer strides, rather than bytesperline in
the format.

Since we're in staging, it could be done with a follow-up patch, though.

Best regards,
Tomasz

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