[PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

[PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

[James Cowgill]

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.

Fixes: b32e48503df0 ("media: controls: Validate H264 stateless controls")
Signed-off-by: James Cowgill <james.cowgill@blaize.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;
-- 
2.49.0

Re: [PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

[Nicolas Dufresne]

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@blaize.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;

Re: [PATCH] media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

[James Cowgill]

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