linux-kernel - Re: [PATCH v5 01/15] media: uapi: HEVC: Add v4l2_ctrl_hevc_ext_sps_[ls]t

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Message-ID: <37da2fe3-41bd-470e-bb6c-93fe35ee1528@collabora.com>
Date: Tue, 16 Dec 2025 15:48:45 -0500
From: Detlev Casanova <detlev.casanova@...labora.com>
To: Hans Verkuil <hverkuil+cisco@...nel.org>, linux-kernel@...r.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
 Heiko Stuebner <heiko@...ech.de>, Ricardo Ribalda <ribalda@...omium.org>,
 Hans Verkuil <hverkuil@...nel.org>, Hans de Goede <hansg@...nel.org>,
 Yunke Cao <yunkec@...gle.com>, Jonathan Corbet <corbet@....net>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 James Cowgill <james.cowgill@...ize.com>, linux-media@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 kernel@...labora.com, Nicolas Dufresne <nicolas.dufresne@...labora.com>
Subject: Re: [PATCH v5 01/15] media: uapi: HEVC: Add
 v4l2_ctrl_hevc_ext_sps_[ls]t_rps controls

Hi Hans,

On 10/24/25 03:55, Hans Verkuil wrote:
> On 23/10/2025 23:42, Detlev Casanova wrote:
>> Some hardware (e.g.: Rockchip's rk3588 hevc decoder) need the
>> long and short term reference information for HEVC decoding.
>>
>> Add controls to provide it as the raw data form the stream.
>>
>> Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>
>> ---
>>   .../media/v4l/ext-ctrls-codec-stateless.rst   | 114 ++++++++++++++++++
>>   .../media/v4l/videodev2.h.rst.exceptions      |   2 +
>>   .../media/v4l/vidioc-queryctrl.rst            |  12 ++
>>   3 files changed, 128 insertions(+)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
>> index 497ae74379f6..7b18e12fafbb 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
>> @@ -2959,6 +2959,120 @@ This structure contains all loop filter related parameters. See sections
>>         - 0x00000004
>>         -
>>   
>> +``V4L2_CID_STATELESS_HEVC_EXT_SPS_LT_RPS (struct)``
>> +    Specifies the list of Long-Term reference sets parameters from the SPS.
>> +    These parameters are defined according to :ref:`hevc`.
>> +    They are described in section 7.4.3.2.1 "General sequence parameter set
>> +    RBSP semantics" of the specification.
>> +    This control is a dynamically sized 1-dimensional array,
>> +    V4L2_CTRL_FLAG_DYNAMIC_ARRAY flag must be set when using it.
> I'd drop this last sentence. It suggests that the application has to set it,
> but is it set by the kernel.
>
> Same for the next control below.
>
> I noticed that this is probably a copy-and-paste from the V4L2_CID_STATELESS_HEVC_SLICE_PARAMS
> documentation: can you post a separate patch removing that same line from the description of
> that control? I think it is a confusing line, and we missed it during the original review
> of V4L2_CID_STATELESS_HEVC_SLICE_PARAMS.
>
> I have another question about these two controls: currently dynamic controls have always at
> least one element. I have been working on supporting zero-sized dynamic controls. Would
> that make sense here? Or will these two controls - if present - always have one element or
> more?
>
> If zero-length dynamic array controls are useful here, then I can clean up my patches and
> post them so you can use it.

I guess that could happen depending on what userspace does, but the size 
of the array is determined by num_long_term_ref_pics_sps and 
num_short_term_ref_pic_sets from v4l2_ctrl_hevc_sps respectively.

If that value is 0, there is no point in setting the (respective) 
control, except for simplifying userspace code I suppose.

So 0-length support is avoidable.

Detlev.

> Regards,
>
> 	Hans
>
>> +
>> +.. c:type:: v4l2_ctrl_hevc_ext_sps_lt_rps
>> +
>> +.. cssclass:: longtable
>> +
>> +.. flat-table:: struct v4l2_ctrl_hevc_ext_sps_lt_rps
>> +    :header-rows:  0
>> +    :stub-columns: 0
>> +    :widths:       1 1 2
>> +
>> +    * - __u16
>> +      - ``lt_ref_pic_poc_lsb_sps``
>> +      - Long term reference picture order count as described in section 7.4.3.2.1
>> +        "General sequence parameter set RBSP semantics" of the specification.
>> +    * - __u8
>> +      - ``flags``
>> +      - See :ref:`Extended Long-Term RPS Flags <hevc_ext_sps_lt_rps_flags>`
>> +
>> +.. _hevc_ext_sps_lt_rps_flags:
>> +
>> +``Extended SPS Long-Term RPS Flags``
>> +
>> +.. cssclass:: longtable
>> +
>> +.. flat-table::
>> +    :header-rows:  0
>> +    :stub-columns: 0
>> +    :widths:       1 1 2
>> +
>> +    * - ``V4L2_HEVC_EXT_SPS_LT_RPS_FLAG_USED_LT``
>> +      - 0x00000001
>> +      - Specifies if the long-term reference picture is used 7.4.3.2.1 "General sequence parameter
>> +        set RBSP semantics" of the specification.
>> +
>> +``V4L2_CID_STATELESS_HEVC_EXT_SPS_ST_RPS (struct)``
>> +    Specifies the list of Short-Term reference sets parameters from the SPS.
>> +    These parameters are defined according to :ref:`hevc`.
>> +    They are described in section 7.4.8 "Short-term reference picture set
>> +    semantics" of the specification.
>> +    This control is a dynamically sized 1-dimensional array,
>> +    V4L2_CTRL_FLAG_DYNAMIC_ARRAY flag must be set when using it.
>> +
>> +.. c:type:: v4l2_ctrl_hevc_ext_sps_st_rps
>> +
>> +.. cssclass:: longtable
>> +
>> +.. flat-table:: struct v4l2_ctrl_hevc_ext_sps_st_rps
>> +    :header-rows:  0
>> +    :stub-columns: 0
>> +    :widths:       1 1 2
>> +
>> +    * - __u8
>> +      - ``delta_idx_minus1``
>> +      - Specifies the delta compare to the index. See details in section 7.4.8 "Short-term
>> +        reference picture set semantics" of the specification.
>> +    * - __u8
>> +      - ``delta_rps_sign``
>> +      - Sign of the delta as specified in section 7.4.8 "Short-term reference picture set
>> +        semantics" of the specification.
>> +    * - __u16
>> +      - ``abs_delta_rps_minus1``
>> +      - Absolute delta RPS as specified in section 7.4.8 "Short-term reference picture set
>> +        semantics" of the specification.
>> +    * - __u8
>> +      - ``num_negative_pics``
>> +      - Number of short-term RPS entries that have picture order count values less than the
>> +        picture order count value of the current picture.
>> +    * - __u8
>> +      - ``num_positive_pics``
>> +      - Number of short-term RPS entries that have picture order count values greater than the
>> +        picture order count value of the current picture.
>> +    * - __u32
>> +      - ``used_by_curr_pic``
>> +      - Bit i specifies if short-term RPS i is used by the current picture.
>> +    * - __u32
>> +      - ``use_delta_flag``
>> +      - Bit i specifies if short-term RPS i is included in the short-term RPS entries.
>> +    * - __u16
>> +      - ``delta_poc_s0_minus1[16]``
>> +      - Specifies the negative picture order count delta for the i-th entry in the short-term RPS.
>> +        See details in section 7.4.8 "Short-term reference picture set semantics" of the
>> +        specification.
>> +    * - __u16
>> +      - ``delta_poc_s1_minus1[16]``
>> +      - Specifies the positive picture order count delta for the i-th entry in the short-term RPS.
>> +        See details in section 7.4.8 "Short-term reference picture set semantics" of the
>> +        specification.
>> +    * - __u8
>> +      - ``flags``
>> +      - See :ref:`Extended Short-Term RPS Flags <hevc_ext_sps_st_rps_flags>`
>> +
>> +.. _hevc_ext_sps_st_rps_flags:
>> +
>> +``Extended SPS Short-Term RPS Flags``
>> +
>> +.. cssclass:: longtable
>> +
>> +.. flat-table::
>> +    :header-rows:  0
>> +    :stub-columns: 0
>> +    :widths:       1 1 2
>> +
>> +    * - ``V4L2_HEVC_EXT_SPS_ST_RPS_FLAG_INTER_REF_PIC_SET_PRED``
>> +      - 0x00000001
>> +      - Specifies if the short-term RPS is predicted from another short term RPS. See details in
>> +        section 7.4.8 "Short-term reference picture set semantics" of the specification.
>> +
>>   .. _v4l2-codec-stateless-av1:
>>   
>>   ``V4L2_CID_STATELESS_AV1_SEQUENCE (struct)``
>> diff --git a/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
>> index c41693115db6..6182b4e2d2ee 100644
>> --- a/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
>> +++ b/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
>> @@ -150,6 +150,8 @@ replace symbol V4L2_CTRL_TYPE_H264_SCALING_MATRIX :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_H264_PRED_WEIGHTS :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_H264_SLICE_PARAMS :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_H264_DECODE_PARAMS :c:type:`V4L.v4l2_ctrl_type`
>> +replace symbol V4L2_CTRL_TYPE_HEVC_EXT_SPS_ST_RPS :c:type:`V4L.v4l2_ctrl_type`
>> +replace symbol V4L2_CTRL_TYPE_HEVC_EXT_SPS_LT_RPS :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_HEVC_SPS :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_HEVC_PPS :c:type:`V4L.v4l2_ctrl_type`
>>   replace symbol V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS :c:type:`V4L.v4l2_ctrl_type`
>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>> index c8baa9430c14..82c8b52e771c 100644
>> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>> @@ -531,6 +531,18 @@ See also the examples in :ref:`control`.
>>         - n/a
>>         - A struct :c:type:`v4l2_ctrl_hevc_decode_params`, containing HEVC
>>   	decoding parameters for stateless video decoders.
>> +    * - ``V4L2_CTRL_TYPE_HEVC_EXT_SPS_LT_RPS``
>> +      - n/a
>> +      - n/a
>> +      - n/a
>> +      - A struct :c:type:`v4l2_ctrl_hevc_ext_sps_lt_rps`, containing HEVC
>> +	extended Long-Term RPS for stateless video decoders.
>> +    * - ``V4L2_CTRL_TYPE_HEVC_EXT_SPS_ST_RPS``
>> +      - n/a
>> +      - n/a
>> +      - n/a
>> +      - A struct :c:type:`v4l2_ctrl_hevc_ext_sps_st_rps`, containing HEVC
>> +	extended Short-Term RPS for stateless video decoders.
>>       * - ``V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR``
>>         - n/a
>>         - n/a