Re: [PATCH] media: bcm2835-unicam: Fix querycap multiple caps

[Jean-Michel Hautbois]

Hi Eugen,

Thank you for the patch.

Two issues with this one, I'm afraid.

Le 11/06/2026 à 08:09, Eugen Hristev a écrit :
> The unicam exposes two video nodes, one for image, another for metadata.
> Querycap should return the right caps for the respective node, not both.
>
> video0:
>
> Capabilities     : 0xa4200001
>          Video Capture
>          I/O MC
>          Streaming
>          Extended Pix Format
>          Device Capabilities
> Device Caps      : 0x24200001
>          Video Capture
>          I/O MC
>          Streaming
>          Extended Pix Format
>
> video1:
>
> Capabilities     : 0xa4a00000
>          Metadata Capture
>          I/O MC
>          Streaming
>          Extended Pix Format
>          Device Capabilities
> Device Caps      : 0x24a00000
>          Metadata Capture
>          I/O MC
>          Streaming
>          Extended Pix Format
>
> Fixes: 392cd78d495f ("media: bcm2835-unicam: Add support for CCP2/CSI2 camera interface")
> Signed-off-by: Eugen Hristev <ehristev@xxxxxxxxxx>
> ---
>   drivers/media/platform/broadcom/bcm2835-unicam.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
> index 8d28ba0b59a3..4bf36ce80047 100644
> --- a/drivers/media/platform/broadcom/bcm2835-unicam.c
> +++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
> @@ -1833,7 +1833,10 @@ static int unicam_querycap(struct file *file, void *priv,
>   	strscpy(cap->driver, UNICAM_MODULE_NAME, sizeof(cap->driver));
>   	strscpy(cap->card, UNICAM_MODULE_NAME, sizeof(cap->card));
>   
> -	cap->capabilities |= V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_META_CAPTURE;
> +	if (is_image_node(node))

First, it does not compile, as node is not declared here.
'struct unicam_node *node = video_drvdata(file);' would be needed.

> +		cap->capabilities |= V4L2_CAP_VIDEO_CAPTURE;
> +	else
> +		cap->capabilities |= V4L2_CAP_META_CAPTURE;
>   
>   	return 0;
>   }

Second, and more important,  I don't think the current behaviour is a bug.
Documentation/userspace-api/media/v4l/vidioc-querycap.rst states about 
the 'capabilities' field:

"The capabilities field should contain a union of all capabilities 
available around the several V4L2 devices exported to userspace.
For all those devices the capabilities field returns the same set of 
capabilities."

Per-node differentiation is the job of 'device_caps', which unicam
already sets correctly when registering each video device (your
v4l2-ctl output shows the Device Caps are already right).

So this looks like working as intended to me, and the patch should be
dropped.

Thanks,
JM

> ---
> base-commit: a87737435cfa134f9cdcc696ba3080759d04cf72
> change-id: 20260611-bcmpiqcap-f893a9ea2da9
>
> Best regards,
> --
> Eugen Hristev <ehristev@xxxxxxxxxx>