Re: [PATCH for v5.3] v4l2-subdev: fix regression in check_pad()

[Janusz Krzysztofik <jmkrzyszt@gmail.com>]

Hi Hans,

On Saturday, June 29, 2019 12:00:24 P.M. CEST Hans Verkuil wrote:
> sd->entity.graph_obj.mdev can be NULL when this function is called, and
> that breaks existing drivers (rcar-vin, but probably others as well).
> 
> Check if sd->entity.num_pads is non-zero instead since that doesn't depend
> on mdev.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Reported-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> Fixes: a8fa55078a77 ("media: v4l2-subdev: Verify arguments in
> v4l2_subdev_call()") ---
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c
> b/drivers/media/v4l2-core/v4l2-subdev.c index 21fb90d66bfc..bc32fc1e0c0b
> 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -124,16 +124,11 @@ static inline int check_which(__u32 which)
>  static inline int check_pad(struct v4l2_subdev *sd, __u32 pad)
>  {
>  #if defined(CONFIG_MEDIA_CONTROLLER)
> -	if (sd->entity.graph_obj.mdev) {
> -		if (pad >= sd->entity.num_pads)
> -			return -EINVAL;
> -		return 0;
> -	}
> +	if (sd->entity.num_pads)

This reverts a change introduced on Sakari's request in v7 of the series which 
is the source of the regression.  The intention was to fail if num_pads == 0 
on a valid media entity. Maybe we should still keep that restriction and fail 
in case mdev is not NULL? In other words: 

-	if (sd->entity.num_pads)
+	if (sd->entity.num_pads || sd->entity.graph_obj.mdev)

Thanks,
Janusz

> +		return pad >= sd->entity.num_pads ? -EINVAL : 0;

This and below look like coding style changes, not related strictly to the 
merit.  Shouldn't they rather be split into a separate patch?

BTW, the current coding style follows original implementation of check_* 
functions present before that series was introduced.  Maybe it would be better 
to keep them unified, i.e., either as is or all updated with the new style.

Thanks,
Janusz

>  #endif
>  	/* allow pad 0 on subdevices not registered as media entities */
> -	if (pad > 0)
> -		return -EINVAL;
> -	return 0;
> +	return pad ? -EINVAL : 0;
>  }
> 
>  static int check_cfg(__u32 which, struct v4l2_subdev_pad_config *cfg)