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

[Janusz Krzysztofik <jmkrzyszt@gmail.com>]

On Saturday, June 29, 2019 2:57:09 P.M. CEST Hans Verkuil wrote:
> On 6/29/19 2:06 PM, Janusz Krzysztofik wrote:
> > 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)
> 
> If an entity has no pads, then it doesn't have pad ops either and this
> function would never be called.

Unless this is a subdevice which doesn't support MC, was updated in the past 
to use pad ops instead of depreciated video ops, so it actually has pad ops 
even if it has num_pads == 0, and is built by a user with 
CONFIG_MEDIA_CONTROLLER=y for some reason.

Thanks,
Janusz

> 
> > 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?
> 
> I'll post a v2, the diff is a lot smaller. I might post a follow-up patch
> to use ? : since that's a lot shorter code.
> 
> Regards,
> 
> 	Hans
> 
> > 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)