Hi Laurent,
On Tue, Jun 25, 2024 at 05:02:47PM +0300, Laurent Pinchart wrote:
> On Sat, Jun 22, 2024 at 04:47:33PM +0000, Sakari Ailus wrote:
> > Hi Laurent,
> >
> > Thanks for the patch.
> >
> > On Wed, Jun 19, 2024 at 04:23:52AM +0300, Laurent Pinchart wrote:
> > > The v4l2_subdev_link_validate() function prints a one-time warning if it
> > > gets called on a link whose source or sink is not a subdev. As links get
> > > validated in the context of their sink, a call to the helper when the
> > > link's sink is not a subdev indicates that the driver has set its
> > > .link_validate() handler to v4l2_subdev_link_validate() on a non-subdev
> > > entity, which is a clear driver bug. On the other hand, the link's
> > > source not being a subdev indicates that the helper is used for a subdev
> > > connected to a video output device, which is a lesser issue, if only
> > > because this is currently common practice.
> > >
> > > There are no drivers left in the kernel that use
> > > v4l2_subdev_link_validate() in a context where it may get called on a
> > > non-subdev sink. Replace the pr_warn_once() with a WARN_ON() in this
> > > case to make sure that new offenders won't be introduced.
> > >
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> > > ---
> > > drivers/media/v4l2-core/v4l2-subdev.c | 14 +++++++++-----
> > > 1 file changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > > index 4f71199bf592..2d5e39c79620 100644
> > > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > > @@ -1451,11 +1451,15 @@ int v4l2_subdev_link_validate(struct media_link *link)
> > > bool states_locked;
> > > int ret;
> > >
> > > - if (!is_media_entity_v4l2_subdev(link->sink->entity) ||
> > > - !is_media_entity_v4l2_subdev(link->source->entity)) {
> > > - pr_warn_once("%s of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
> > > - !is_media_entity_v4l2_subdev(link->sink->entity) ?
> > > - "sink" : "source",
> > > + /*
> > > + * Links are validated in the context of the sink entity. Usage of this
> > > + * helper on a sink that is not a subdev is a clear driver bug.
> > > + */
> > > + if (WARN_ON(!is_media_entity_v4l2_subdev(link->sink->entity)))
> > > + return -EINVAL;
> >
> > WARN*() is nowadays deprecated.
>
> Why so ? I've followed a recent discussion where some people pointed out
> they disliked WARN*() due to panic-on-warn, but I didn't see any
> conclusion there that deprecated WARN*().
Fair enough, there seems to have been more discussion.
As this is still user-triggerable, this should be WARN_ON_ONCE() to prevent
the user from filling the logs, intentionally or not.
>
> > Could you continue to use pr_warn_once()
> > for this (or dev_warn_one())?
>
> I think a WARN_ON() is the right option here. A failure indicates a
> clear driver bug, we should be as loud as possible to make sure it gets
> noticed during development.
>
> > > +
> > > + if (!is_media_entity_v4l2_subdev(link->source->entity)) {
> > > + pr_warn_once("source of link '%s':%u->'%s':%u is not a V4L2 sub-device, driver bug!\n",
> > > link->source->entity->name, link->source->index,
> > > link->sink->entity->name, link->sink->index);
> > > return 0;
>
--
Kind regards,
Sakari Ailus
