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

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Message-ID: <a8lp0h15oaibdu1pqrkhsu8nh32v423tur@4ax.com>
Date:   Wed, 16 Feb 2022 10:54:29 +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,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Subject: Re: [RFC v2 7/8] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET control

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.

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,