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

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Message-ID: <c31d9556-7ace-432d-b50e-df566900f535@blaize.com>
Date: Thu, 5 Jun 2025 00:14:07 +0100
From: James Cowgill <james.cowgill@...ize.com>
To: Nicolas Dufresne <nicolas@...fresne.ca>,
        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 Nicolas,

On 04/06/2025 16:35, Nicolas Dufresne wrote:
> 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.

That wording seems fine to me.

And yes this patch was just based on me reading the code - it doesn't
fix any actual breakage (at least for now).

Thanks,
James