Re: [PATCH 1/1] media: subdev: Make get_fmt on INTERNAL pads without STREAMS an error

[Hans Verkuil <hverkuil+cisco@kernel.org>]

On 06/10/2026 11:29, Sakari Ailus wrote:
> Internal pads should only be accessible to file handles with
> V4L2_SUBDEV_CLIENT_CAP_STREAMS flag set. Return an error otherwise.
> 
> Fixes: 49cdf56876d3 ("media: mc: Add INTERNAL pad flag")
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-subdev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index a07d77e584c3..7cb5a40f0f8c 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -854,8 +854,13 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
>  	case VIDIOC_SUBDEV_G_FMT: {
>  		struct v4l2_subdev_format *format = arg;
>  
> -		if (!client_supports_streams)
> +		if (!client_supports_streams) {
> +			if (format->pad < sd->entity.num_pads &&
> +			    sd->entity.pads[format->pad].flags & MEDIA_PAD_FL_INTERNAL)
> +				return -EINVAL;
> +
>  			format->stream = 0;
> +		}
>  
>  		memset(format->reserved, 0, sizeof(format->reserved));
>  		memset(format->format.reserved, 0, sizeof(format->format.reserved));
> 

There is no documentation that I can find that says that MEDIA_PAD_FL_INTERNAL is only available
if V4L2_SUBDEV_CLIENT_CAP_STREAMS is set.

I think this needs some more thought: if internal pads are only available if that cap is set,
then I expect that a lot more ioctls will need this check. In that case the check should become
a helper function.

But how does this affect e.g. G_TOPOLOGY or ENUM_LINKS? If the cap is not set, should internal
pads still be reported?

And you need checks in v4l2-compliance, ensuring that trying to access internal pads without
that cap will indeed fail.

Ideally you would like to have this emulated in vimc as well.

In other words, I think this needs more work, both in the core and w.r.t. documentation.

Regards,

	Hans