Re: [PATCH v5 09/17] media: uapi: HEVC: Define V4L2_CID_STATELESS_HEVC_SLICE_PARAMS as a dynamic array

From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>,
	mchehab@kernel.org, hverkuil@xs4all.nl,
	ezequiel@vanguardiasur.com.ar, p.zabel@pengutronix.de,
	gregkh@linuxfoundation.org, mripard@kernel.org,
	paul.kocialkowski@bootlin.com,  wens@csie.org,
	jernej.skrabec@gmail.com, samuel@sholland.org
Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	 linux-rockchip@lists.infradead.org,
	linux-staging@lists.linux.dev,
	 linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev,  sebastian.fricke@collabora.com
Subject: Re: [PATCH v5 09/17] media: uapi: HEVC: Define V4L2_CID_STATELESS_HEVC_SLICE_PARAMS as a dynamic array
Date: Fri, 08 Apr 2022 14:53:20 -0400	[thread overview]
Message-ID: <3179e400d52704d11dd150bf4270dab4c1064cad.camel@collabora.com> (raw)
In-Reply-To: <20220407152940.738159-10-benjamin.gaignard@collabora.com>

Le jeudi 07 avril 2022 à 17:29 +0200, Benjamin Gaignard a écrit :
> Make explicit that V4L2_CID_STATELESS_HEVC_SLICE_PARAMS control is
> a dynamic array control type.
> Some drivers may be able to receive multiple slices in one control
> to improve decoding performance.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> ---
>  Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 2 ++
>  include/media/hevc-ctrls.h                                | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 7fcc6c2bac4c..1aaf3b84b584 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -2964,6 +2964,8 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>      These bitstream parameters are defined according to :ref:`hevc`.
>      They are described in section 7.4.7 "General slice segment header
>      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_slice_params
>  
> diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
> index 96a9b71d1def..28049e1a8a07 100644
> --- a/include/media/hevc-ctrls.h
> +++ b/include/media/hevc-ctrls.h
> @@ -314,6 +314,9 @@ struct v4l2_hevc_pred_weight_table {
>  /**
>   * v4l2_ctrl_hevc_slice_params - HEVC slice parameters
>   *
> + * This control is a dynamically sized 1-dimensional array,
> + * V4L2_CTRL_FLAG_DYNAMIC_ARRAY flag must be set when using it.
> + *

I'm not sure about this comment, but I'm sure you forgot:

--- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
@@ -1505,6 +1505,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum
v4l2_ctrl_type *type,
                break;
        case V4L2_CID_STATELESS_HEVC_SLICE_PARAMS:
                *type = V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS;
+               *flags |= V4L2_CTRL_FLAG_DYNAMIC_ARRAY;
                break;
        case V4L2_CID_STATELESS_HEVC_SCALING_MATRIX:
                *type = V4L2_CTRL_TYPE_HEVC_SCALING_MATRIX;

Also, in AV1 we have V4L2_AV1_MAX_TILE_COUNT, which can be used in cfg.dims,
something the driver will actually set. We could have

#define V4L2_HEVC_MAX_TILE_COUNT 600

And drives can set:

   .dims = { V4L2_HEVC_MAX_TILE_COUNT },

In the control config.

>   * @bit_size: size (in bits) of the current slice data
>   * @data_bit_offset: offset (in bits) to the video data in the current slice data
>   * @nal_unit_type: specifies the coding type of the slice (B, P or I)


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