linux-kernel - Re: [PATCH v2] v4l2-subdev: Return -EOPNOTSUPP for unsupported pad type in call_get_frame

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Message-ID: <20241009145730.GA16955@pendragon.ideasonboard.com>
Date: Wed, 9 Oct 2024 17:57:30 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Prabhakar <prabhakar.csengg@...il.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	Biju Das <biju.das.jz@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2] v4l2-subdev: Return -EOPNOTSUPP for unsupported pad
 type in call_get_frame_desc()

On Wed, Oct 09, 2024 at 06:01:45AM +0000, Sakari Ailus wrote:
> Hi Laurent,
> 
> On Mon, Oct 07, 2024 at 09:16:54PM +0300, Laurent Pinchart wrote:
> > Hi Prabhakar,
> > 
> > Thank you for the patch.
> > 
> > On Mon, Oct 07, 2024 at 01:38:09PM +0100, Prabhakar wrote:
> > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > 
> > > The `get_frame_desc()` operation should always be called on a source pad,
> > > which is indicated by the `MEDIA_PAD_FL_SOURCE` flag. This patch adds a
> > > check in `call_get_frame_desc()` to ensure that the `MEDIA_PAD_FL_SOURCE`
> > > flag is set for the pad before invoking `get_frame_desc()`. If the pad is
> > > not a source pad, the function will return an `-EOPNOTSUPP` error,
> > > signaling that the operation is not supported on non-source pads.
> > > 
> > > Suggested-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > ---
> > > v1->v2
> > > - Added a check for CONFIG_MEDIA_CONTROLLER, as the `entity` member in 
> > >   `struct v4l2_subdev` is only available when CONFIG_MEDIA_CONTROLLER
> > >   is enabled.
> > > ---
> > >  drivers/media/v4l2-core/v4l2-subdev.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > > index de9ac67574bb..446fbc3805c7 100644
> > > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > > @@ -325,6 +325,11 @@ static int call_get_frame_desc(struct v4l2_subdev *sd, unsigned int pad,
> > >  	unsigned int i;
> > >  	int ret;
> > >  
> > > +#if defined(CONFIG_MEDIA_CONTROLLER)
> > > +	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
> > 
> > As this should really not happen, I wonder if we shouldn't be more
> > vocal:
> > 
> > 	if (WARN_ON(!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE)))
> > 
> > Sakari, what do you think ? Either way,
> 
> I wouldn't as this is probably going to be user-triggerable. The problem
> shouldn't be too hard to find out either.

I don't expect .get_frame_desc() to be callable with user-controllable
arguments, but I'm OK not using WARN_ON().

> > Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> 
> Thanks!

-- 
Regards,

Laurent Pinchart