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

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Date:   Wed, 16 Feb 2022 17:35:56 +0000
From:   John Cox <jc@...esim.co.uk>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
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

On Wed, 16 Feb 2022 18:19:10 +0100, you wrote:

>
>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) ?

I meant num_entry_point_offsets field in each slice parameter control +
one control for the entry points themselves.  Given that you have a
varible number of entry points associated with each slice and you have a
variable number of slices this seems the easiest answer to me both to
construct in userspace and to use in the driver.

Regards

JC

>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,