linux-kernel - Re: [PATCH v6 16/17] media: uapi: Change data_bit

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Message-ID: <3175529.44csPzL39Z@kista>
Date:   Sun, 29 May 2022 08:45:57 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     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, samuel@...lland.org,
        nicolas.dufresne@...labora.com, andrzej.p@...labora.com,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     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,
        kernel@...labora.com,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Subject: Re: [PATCH v6 16/17] media: uapi: Change data_bit_offset definition

Dne petek, 27. maj 2022 ob 16:31:33 CEST je Benjamin Gaignard napisal(a):
> 'F.7.3.6.1 General slice segment header syntax' section of HEVC
> specification describes that a slice header always end aligned on
> byte boundary, therefore we only need to provide the data offset in bytes.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> ---
>  Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 4 ++--
>  drivers/staging/media/sunxi/cedrus/cedrus_h265.c          | 2 +-
>  include/media/hevc-ctrls.h                                | 4 ++--
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/
Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 48a8825a001b..37079581c661 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -3008,8 +3008,8 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>        - ``bit_size``
>        - Size (in bits) of the current slice data.
>      * - __u32
> -      - ``data_bit_offset``
> -      - Offset (in bits) to the video data in the current slice data.
> +      - ``data_byte_offset``
> +      - Offset (in bytes) to the video data in the current slice data.
>      * - __u32
>        - ``num_entry_point_offsets``
>        - Specifies the number of entry point offset syntax elements in the 
slice header.
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c b/drivers/
staging/media/sunxi/cedrus/cedrus_h265.c
> index 411601975124..835454239f73 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> @@ -405,7 +405,7 @@ static void cedrus_h265_setup(struct cedrus_ctx *ctx,
>  	/* Initialize bitstream access. */
>  	cedrus_write(dev, VE_DEC_H265_TRIGGER, 
VE_DEC_H265_TRIGGER_INIT_SWDEC);
>  
> -	cedrus_h265_skip_bits(dev, slice_params->data_bit_offset);
> +	cedrus_h265_skip_bits(dev, slice_params->data_byte_offset * 8);

While it's true that actual data starts on 8-bit aligned address, Cedrus for 
some reason needs offset which points at the end of the header, before 
alignment. There is very simple way to determine that, but unfortunately this 
means reading source buffer.

In short, above code won't work. I'll provide a fix.

Best regards,
Jernej

>  
>  	/* Bitstream parameters. */
>  
> diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
> index 9abca1a75bd4..936ff693967b 100644
> --- a/include/media/hevc-ctrls.h
> +++ b/include/media/hevc-ctrls.h
> @@ -312,7 +312,7 @@ struct v4l2_hevc_pred_weight_table {
>   * V4L2_CTRL_FLAG_DYNAMIC_ARRAY flag must be set when using it.
>   *
>   * @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
> + * @data_byte_offset: offset (in bytes) to the video data in the current 
slice data
>   * @num_entry_point_offsets: specifies the number of entry point offset syntax
>   *			     elements in the slice header.
>   * @nal_unit_type: specifies the coding type of the slice (B, P or I)
> @@ -356,7 +356,7 @@ struct v4l2_hevc_pred_weight_table {
>   */
>  struct v4l2_ctrl_hevc_slice_params {
>  	__u32	bit_size;
> -	__u32	data_bit_offset;
> +	__u32	data_byte_offset;
>  	__u32	num_entry_point_offsets;
>  	/* ISO/IEC 23008-2, ITU-T Rec. H.265: NAL unit header */
>  	__u8	nal_unit_type;
> -- 
> 2.32.0
> 
>