Re: [PATCH] media: v4l2-fwnode: Fix subdev owner overwritten in v4l2_async_register_subdev_sensor()

[Frank Li]

On Fri, May 22, 2026 at 05:30:58PM +0300, Mirela Rabulea wrote:
> Hi Frank,
>
> On 5/21/26 21:45, Frank Li wrote:
> > On Thu, May 21, 2026 at 03:26:45PM +0300, Mirela Rabulea wrote:
> > > The v4l2 helper v4l2_async_register_subdev_sensor() calls
> > > v4l2_async_register_subdev(), which is a macro that expands to
> > > __v4l2_async_register_subdev(sd,THIS_MODULE). Since the macro is expanded
> > > inside v4l2-fwnode.c, THIS_MODULE resolves to the v4l2-fwnode module
> > > rather than the sensor driver module that originally set sd->owner. When
> > > v4l2-fwnode is built-in, THIS_MODULE evaluates to NULL, which then
> > > overwrites the sensor driver's owner with NULL.
> > This is problem. but this patch can't resolve problem 100% because
> > many sensor driver have not init sd->owner before call
> > v4l2_async_register_subdev_sensor()
> Thanks for the suggestion. From what I see, all sensor drivers that use
> v4l2_async_register_subdev_sensor() also use v4l2_i2c_subdev_init(), which
>
> sets sd->owner. However, since your proposal looks more robust and there is
> already a similar solution accepted for v4l2_async_register_subdev(), I will
> send a v2 with that approach.

Okay, that's also make sense. let's wait for maintainers' opinion.

Frank
>
> Thanks,
>
> Mirela
>
> >
> > suggest solution like what v4l2_async_register_subdev() did
> >
> > rename v4l2_async_register_subdev_sensor() to
> > __v4l2_async_register_subdev_sensor(truct v4l2_subdev *sd, module *this)
> >
> > #define v4l2_async_register_subdev_sensor(sd)
> > 	__v4l2_async_register_subdev_sensor(sd, THIS_MODULE)
> >
> > Frank
> >
> > > This causes the problem that the sensor module's reference count is never
> > > incremented during async registration, so the module can be removed while
> > > the subdevice is still in use by a notifier (e.g., a CSI-2 receiver
> > > bridge driver).
> > >
> > > Fix this by calling __v4l2_async_register_subdev() directly with
> > > sd->owner, which preserves the module owner that the sensor driver set
> > > during probe via v4l2_i2c_subdev_init() or direct assignment.
> > >
> > > Fixes: aef69d54755d ("media: v4l: fwnode: Add a convenience function for registering sensors")
> > >
> > > Signed-off-by: Mirela Rabulea <mirela.rabulea@xxxxxxx>
> > > ---
> > >   drivers/media/v4l2-core/v4l2-fwnode.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/v4l2-core/v4l2-fwnode.c b/drivers/media/v4l2-core/v4l2-fwnode.c
> > > index 77f3298821b5..57284b7adddf 100644
> > > --- a/drivers/media/v4l2-core/v4l2-fwnode.c
> > > +++ b/drivers/media/v4l2-core/v4l2-fwnode.c
> > > @@ -1282,7 +1282,7 @@ int v4l2_async_register_subdev_sensor(struct v4l2_subdev *sd)
> > >   	if (ret < 0)
> > >   		goto out_cleanup;
> > >
> > > -	ret = v4l2_async_register_subdev(sd);
> > > +	ret = __v4l2_async_register_subdev(sd, sd->owner);
> > >   	if (ret < 0)
> > >   		goto out_unregister;
> > >
> > > --
> > > 2.43.0
> > >