linux-kernel - Re: [PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR

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Message-ID: <254309f1c527d782e0c50c425602c94683f395b6.camel@ndufresne.ca>
Date: Wed, 04 Jun 2025 11:35:22 -0400
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: James Cowgill <james.cowgill@...ize.com>, Mauro Carvalho Chehab
	 <mchehab@...nel.org>, Hans Verkuil <hverkuil@...all.nl>, Ezequiel Garcia
	 <ezequiel@...guardiasur.com.ar>
Cc: "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>, 
 "linux-kernel@...r.kernel.org"
	 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

Hi James,

Le mercredi 04 juin 2025 à 14:38 +0000, James Cowgill a écrit :
> The `separate_colour_plane_flag` element is only present in the SPS if
> `chroma_format_idc == 3`, so the corresponding flag should be disabled
> whenever that is not the case and not just on profiles where
> `chroma_format_idc` is not present.


The fix seems correct indeed. This has no incidence on any current driver, since
there is nothing upstream that supports decoding 4:4:4. Would you mind if we
extend the commit with something such as:

	This prevents invalid flags being passed, though no upstream drivers
	currently supports YCbCr 4:4:4 decoding.

Feel free to to suggest a better edit. It will make stable people (and bot) aware
of the patch priority. I can make the edit while applying.

regards,
Nicolas

> 
> Fixes: b32e48503df0 ("media: controls: Validate H264 stateless controls")
> Signed-off-by: James Cowgill <james.cowgill@...ize.com>
> ---
>  drivers/media/v4l2-core/v4l2-ctrls-core.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> index 90d25329661e..b45809a82f9a 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> @@ -968,12 +968,12 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
>  
>  			p_h264_sps->flags &=
>  				~V4L2_H264_SPS_FLAG_QPPRIME_Y_ZERO_TRANSFORM_BYPASS;
> -
> -			if (p_h264_sps->chroma_format_idc < 3)
> -				p_h264_sps->flags &=
> -					~V4L2_H264_SPS_FLAG_SEPARATE_COLOUR_PLANE;
>  		}
>  
> +		if (p_h264_sps->chroma_format_idc < 3)
> +			p_h264_sps->flags &=
> +				~V4L2_H264_SPS_FLAG_SEPARATE_COLOUR_PLANE;
> +
>  		if (p_h264_sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY)
>  			p_h264_sps->flags &=
>  				~V4L2_H264_SPS_FLAG_MB_ADAPTIVE_FRAME_FIELD;