linux-kernel - Re: [RFC v2 7/8] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT

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Message-ID: <846370ec-5c9e-e4cb-eccf-0b0c6bdbc847@collabora.com>
Date:   Wed, 16 Feb 2022 18:19:10 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...labora.com>
To:     John Cox <jc@...esim.co.uk>
Cc:     mchehab@...nel.org, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        mripard@...nel.org, paul.kocialkowski@...tlin.com, wens@...e.org,
        jernej.skrabec@...il.com, hverkuil-cisco@...all.nl,
        jonas@...boo.se, nicolas@...fresne.ca, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        kernel@...labora.com, knaerzche@...il.com
Subject: Re: [RFC v2 7/8] media: uapi: Add
 V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET control


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@...labora.com>
>> ---
>> 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,