Hi Hans,
Many thanks for reviewing these.
On Mon, Feb 05, 2024 at 03:56:22PM +0100, Hans Verkuil wrote:
> On 20/12/2023 11:37, Sakari Ailus wrote:
> > The video device depends on the existence of its media device --- if there
> > is one. Acquire a reference to it.
> >
> > Note that when the media device release callback is used, then the V4L2
> > device release callback is ignored and a warning is issued if both are
> > set.
> >
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> > drivers/media/v4l2-core/v4l2-dev.c | 51 ++++++++++++++++++++----------
> > 1 file changed, 34 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> > index d13954bd31fd..c1e4995eaf5c 100644
> > --- a/drivers/media/v4l2-core/v4l2-dev.c
> > +++ b/drivers/media/v4l2-core/v4l2-dev.c
> > @@ -176,6 +176,11 @@ static void v4l2_device_release(struct device *cd)
> > {
> > struct video_device *vdev = to_video_device(cd);
> > struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
> > + bool v4l2_dev_has_release = v4l2_dev->release;
> > +#ifdef CONFIG_MEDIA_CONTROLLER
> > + struct media_device *mdev = v4l2_dev->mdev;
> > + bool mdev_has_release = mdev && mdev->ops && mdev->ops->release;
> > +#endif
> >
> > mutex_lock(&videodev_lock);
> > if (WARN_ON(video_devices[vdev->minor] != vdev)) {
> > @@ -198,8 +203,8 @@ static void v4l2_device_release(struct device *cd)
> >
> > mutex_unlock(&videodev_lock);
> >
> > -#if defined(CONFIG_MEDIA_CONTROLLER)
> > - if (v4l2_dev->mdev && vdev->vfl_dir != VFL_DIR_M2M) {
> > +#ifdef CONFIG_MEDIA_CONTROLLER
> > + if (mdev && vdev->vfl_dir != VFL_DIR_M2M) {
> > /* Remove interfaces and interface links */
> > media_devnode_remove(vdev->intf_devnode);
> > if (vdev->entity.function != MEDIA_ENT_F_UNKNOWN)
> > @@ -207,23 +212,31 @@ static void v4l2_device_release(struct device *cd)
> > }
> > #endif
> >
> > - /* Do not call v4l2_device_put if there is no release callback set.
> > - * Drivers that have no v4l2_device release callback might free the
> > - * v4l2_dev instance in the video_device release callback below, so we
> > - * must perform this check here.
> > - *
> > - * TODO: In the long run all drivers that use v4l2_device should use the
> > - * v4l2_device release callback. This check will then be unnecessary.
> > - */
> > - if (v4l2_dev->release == NULL)
> > - v4l2_dev = NULL;
> > -
> > /* Release video_device and perform other
> > cleanups as needed. */
> > vdev->release(vdev);
> >
> > - /* Decrease v4l2_device refcount */
> > - if (v4l2_dev)
> > +#ifdef CONFIG_MEDIA_CONTROLLER
> > + if (mdev)
> > + media_device_put(mdev);
> > +
> > + /*
> > + * Generally both struct media_device and struct v4l2_device are
> > + * embedded in the same driver's context struct so having a release
> > + * callback in both is a bug.
> > + */
> > + WARN_ON(v4l2_dev_has_release && mdev_has_release);
>
> How about:
>
> if (WARN_ON(v4l2_dev_has_release && mdev_has_release))
> v4l2_dev_has_release = false;
>
> > +#endif
> > +
> > + /*
> > + * Decrease v4l2_device refcount, but only if the media device doesn't
> > + * have a release callback.
> > + */
> > + if (v4l2_dev_has_release
> > +#ifdef CONFIG_MEDIA_CONTROLLER
> > + && !mdev_has_release
> > +#endif
> > + )
>
> Then this change is no longer needed.
Good idea.
I'll also rename v4l2_dev_has_release as v4l2_dev_call_release.
>
> General question: do we have drivers today that set both release functions?
> Because that would now cause a WARN in the kernel log with this patch.
Indeed, the intention is to be vocal about it.
The only user of the v4l2_device release function I could find is
drivers/media/radio/dsbr100.c . I may have missed some but it certainly
isn't commonly used. Maybe we could try to drop refcounting from
v4l2_device later on?
>
> > v4l2_device_put(v4l2_dev);
> > }
> >
> > @@ -792,11 +805,14 @@ static int video_register_media_controller(struct video_device *vdev)
> > u32 intf_type;
> > int ret;
> >
> > - /* Memory-to-memory devices are more complex and use
> > + /*
> > + * Memory-to-memory devices are more complex and use
> > * their own function to register its mc entities.
> > */
> > - if (!vdev->v4l2_dev->mdev || vdev->vfl_dir == VFL_DIR_M2M)
> > + if (!vdev->v4l2_dev->mdev || vdev->vfl_dir == VFL_DIR_M2M) {
> > + media_device_get(vdev->v4l2_dev->mdev);
> > return 0;
> > + }
> >
> > vdev->entity.obj_type = MEDIA_ENTITY_TYPE_VIDEO_DEVICE;
> > vdev->entity.function = MEDIA_ENT_F_UNKNOWN;
> > @@ -875,6 +891,7 @@ static int video_register_media_controller(struct video_device *vdev)
> >
> > /* FIXME: how to create the other interface links? */
> >
> > + media_device_get(vdev->v4l2_dev->mdev);
> > #endif
> > return 0;
> > }
--
Kind regards,
Sakari Ailus
