linux-kernel - Re: [PATCH] media: docs: dev-decoder: Trigger dynamic source change for colorspace

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Message-ID: <dcae7fbb810ebfa6e539c3b45c20e1d659600d80.camel@ndufresne.ca>
Date: Wed, 08 Jan 2025 14:34:19 -0500
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Ming Qian <ming.qian@....nxp.com>, mchehab@...nel.org, 
	hverkuil-cisco@...all.nl
Cc: shawnguo@...nel.org, robh+dt@...nel.org, s.hauer@...gutronix.de, 
	kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
 xiahong.bao@....com, 	eagle.zhou@....com, tao.jiang_2@....com,
 imx@...ts.linux.dev, 	linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, 	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] media: docs: dev-decoder: Trigger dynamic source change
 for colorspace

Hi,

Le mardi 07 janvier 2025 à 14:36 +0900, Ming Qian a écrit :
> If colorspace changes, the client needs to renegotiate the pipeline,
> otherwise the decoded frame may not be displayed correctly.
> 
> If it can trigger an source change event, then client can switch to the
> correct stream setting. And each frame can be displayed properly.
> 
> So add colorspace as a trigger parameter for dynamic resolution change.
> 
> Signed-off-by: Ming Qian <ming.qian@....nxp.com>
> ---
>  Documentation/userspace-api/media/v4l/dev-decoder.rst | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/dev-decoder.rst b/Documentation/userspace-api/media/v4l/dev-decoder.rst
> index ef8e8cf31f90..49566569ad26 100644
> --- a/Documentation/userspace-api/media/v4l/dev-decoder.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-decoder.rst
> @@ -932,7 +932,9 @@ reflected by corresponding queries):
>  
>  * the minimum number of buffers needed for decoding,
>  
> -* bit-depth of the bitstream has been changed.
> +* bit-depth of the bitstream has been changed,
> +
> +* colorspace of the bitstream has been changed.

Did you really mean colorspace in the way this term is used in V4L2 ? What we
want this event to be used for is when the capture storage size or amount
changes, perhaps you mean when the capture pixelformat changes ? This will
indeed happen if you change the bit-depth, subsampling (not mentioned here
either) or change the way colors are repsented (RGB, YCbCr, etc.).

>  
>  Whenever that happens, the decoder must proceed as follows:
>