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

[Tomasz Figa <tfiga@chromium.org>]

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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