linux-kernel - Re: [PATCH v5 04/17] media: uapi: HEVC: Add missing fields in HEVC controls

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Message-ID: <20220425135449.oapsrqqyq34s2ii3@basti-XPS-13-9310>
Date:   Mon, 25 Apr 2022 15:54:49 +0200
From:   Sebastian Fricke <sebastian.fricke@...labora.com>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     mchehab@...nel.org, hverkuil@...all.nl,
        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, samuel@...lland.org,
        nicolas.dufresne@...labora.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v5 04/17] media: uapi: HEVC: Add missing fields in HEVC
 controls

On 07.04.2022 17:29, Benjamin Gaignard wrote:
>Complete the HEVC controls with missing fields from H.265 specifications.
>Even if these fields aren't used by the current mainlined drivers
>they will be need for (at least) rkvdec driver.

s/be need/be required/
or
s/be need/be needed/

s/rkvdec/the rkvdec/

>
>Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>---
> .../media/v4l/ext-ctrls-codec.rst             | 19 +++++++++++++++++++
> include/media/hevc-ctrls.h                    |  6 +++++-
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
>diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>index 4cd7c541fc30..dbb08603217b 100644
>--- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>@@ -2661,6 +2661,16 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>     :stub-columns: 0
>     :widths:       1 1 2
>
>+    * - __u8
>+      - ``video_parameter_set_id``
>+      - Specifies the value of the vps_video_parameter_set_id of the active VPS
>+        as descibed in section "7.4.3.2.1 General sequence parameter set RBSP semantics"
>+        of H.265 specifications.
>+    * - __u8
>+      - ``seq_parameter_set_id``
>+      - Provides an identifier for the SPS for reference by other syntax elements
>+        as descibed in section "7.4.3.2.1 General sequence parameter set RBSP semantics"
>+        of H.265 specifications.
>     * - __u16
>       - ``pic_width_in_luma_samples``
>       -
>@@ -2800,6 +2810,9 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>     :stub-columns: 0
>     :widths:       1 1 2
>
>+    * - __u8
>+      - ``pic_parameter_set_id``
>+      - Identifies the PPS for reference by other syntax elements.
>     * - __u8
>       - ``num_extra_slice_header_bits``
>       -
>@@ -3026,6 +3039,12 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>     * - __u8
>       - ``ref_idx_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX]``
>       - The list of L1 reference elements as indices in the DPB.
>+    * - __u16
>+      - ``short_term_ref_pic_set_size``
>+      - Specifies the size of short-term reference pictures set included in the SPS.

s/size of/size of the/

Section 7.4.8 depicts that the st_ref_pic_set syntax
structure can be part of the SPS or the slice header.

I think we should mention that we talk about the size of the st_ref_pic_set
syntax structure from section 7.4.8 of the specification. 

>+    * - __u16
>+      - ``long_term_ref_pic_set_size``
>+      - Specifies the size of long-term reference pictures set include in the SPS.

s/size of/size of the/

Can we make this a bit more helpful? The specification doesn't contain
a similar structure to `st_ref_pic_set` for long term pictures. So, as a
programmer this leaves me guessing:
- Which syntax structure's size are we talking about?
- Does this correlate to any of the existing sections of the
specification?
Because in the end, I feel like this documentation should be able to
help a programmer to provide the correct data for the uABI.

Greetings,
Sebastian

>     * - __u8
>       - ``padding``
>       - Applications and drivers must set this to zero.
>diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
>index 01ccda48d8c5..a329e086a89a 100644
>--- a/include/media/hevc-ctrls.h
>+++ b/include/media/hevc-ctrls.h
>@@ -58,6 +58,8 @@ enum v4l2_mpeg_video_hevc_start_code {
> /* The controls are not stable at the moment and will likely be reworked. */
> struct v4l2_ctrl_hevc_sps {
> 	/* ISO/IEC 23008-2, ITU-T Rec. H.265: Sequence parameter set */
>+	__u8	video_parameter_set_id;
>+	__u8	seq_parameter_set_id;
> 	__u16	pic_width_in_luma_samples;
> 	__u16	pic_height_in_luma_samples;
> 	__u8	bit_depth_luma_minus8;
>@@ -108,6 +110,7 @@ struct v4l2_ctrl_hevc_sps {
>
> struct v4l2_ctrl_hevc_pps {
> 	/* ISO/IEC 23008-2, ITU-T Rec. H.265: Picture parameter set */
>+	__u8	pic_parameter_set_id;
> 	__u8	num_extra_slice_header_bits;
> 	__u8	num_ref_idx_l0_default_active_minus1;
> 	__u8	num_ref_idx_l1_default_active_minus1;
>@@ -199,7 +202,8 @@ struct v4l2_ctrl_hevc_slice_params {
> 	__u32	slice_segment_addr;
> 	__u8	ref_idx_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
> 	__u8	ref_idx_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>-
>+	__u16	short_term_ref_pic_set_size;
>+	__u16	long_term_ref_pic_set_size;
> 	__u8	padding;
>
> 	/* ISO/IEC 23008-2, ITU-T Rec. H.265: Weighted prediction parameter */
>-- 
>2.32.0
>