Re: [RFC v2 7/8] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET control

[Benjamin Gaignard]

Le 16/02/2022 à 11:54, John Cox a écrit :
> On Tue, 15 Feb 2022 12:01:02 +0100, you wrote:
>
> > The number of 'entry point offset' could be very variable.
> > Rather than use a large static array define a v4l2 dynamic array
> > of integer control.
> > The number of entry point offsets is reported by the elems field.
> If we are going to support multiple slice headers in a single control
> then we are going to need to know how to split these entries between
> them as I assume that the entry point offset entries for all slice
> headers would just be catenated here.  You could add extra elements here
> or generate a completely new control but I think it would be easier to
> reinstate the num_entry_point_offsets field in the slice_params
> structure (its a field that userpace has in its hand anyway so its no
> effort for it to fill in).  num_entry_point_offsets is a field that RPi
> wants (without needing the entry points themselves) so that would help
> me.

Would that means num_entry_point_offsets field in slice parameter control
+ one control for the entry points themselves ?
or the both on slice parameter control (like now) ?

Regards
Benjamin

> Regards
>
> John Cox
>
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> > ---
> > version 2:
> > - Define a new CID for entry point offsets parameters
> > .../userspace-api/media/v4l/ext-ctrls-codec.rst          | 9 +++++++++
> > include/uapi/linux/v4l2-controls.h                       | 1 +
> > 2 files changed, 10 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > index c3ae97657fa7..679595e94643 100644
> > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > @@ -3101,6 +3101,15 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
> >
> >      \normalsize
> >
> > +``V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS (integer)``
> > +    Specifies the i-th entry point offset in bytes and is represented by
> > +    offset_len_minus1 plus 1 bits.
> > +    This control is a dynamically sized array. The number of entry point
> > +    offsets is reported by the ``elems`` field.
> > +    This bitstream parameter is defined according to :ref:`hevc`.
> > +    They are described in section 7.4.7.1 "General slice segment header
> > +    semantics" of the specification.
> > +
> > ``V4L2_CID_STATELESS_HEVC_SCALING_MATRIX (struct)``
> >      Specifies the HEVC scaling matrix parameters used for the scaling process
> >      for transform coefficients.
> > diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> > index 27f5d272dc43..700e6cce958c 100644
> > --- a/include/uapi/linux/v4l2-controls.h
> > +++ b/include/uapi/linux/v4l2-controls.h
> > @@ -2314,6 +2314,7 @@ struct v4l2_ctrl_vp9_compressed_hdr {
> > #define V4L2_CID_STATELESS_HEVC_DECODE_PARAMS	(V4L2_CID_CODEC_STATELESS_BASE + 404)
> > #define V4L2_CID_STATELESS_HEVC_DECODE_MODE	(V4L2_CID_CODEC_STATELESS_BASE + 405)
> > #define V4L2_CID_STATELESS_HEVC_START_CODE	(V4L2_CID_CODEC_STATELESS_BASE + 406)
> > +#define V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET	(V4L2_CID_CODEC_STATELESS_BASE + 407)
> >
> > enum v4l2_stateless_hevc_decode_mode {
> > 	V4L2_STATELESS_HEVC_DECODE_MODE_SLICE_BASED,