Hi Laurent,
Thank you for reviewing the set!
On Wed, Feb 07, 2024 at 01:13:44PM +0200, Laurent Pinchart wrote:
> 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.
>
> Why is that ? The two are distinct objects, why can't they both have a
> release function ?
You could, in principle, but in practice both of the structs are part of
the same driver's device context struct which is a single allocation. You
can only have a single release callback for it.
>
> > >
> > > 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.
> >
> > 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.
> >
> > > 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 you fix the comment style as a drive-by change, you could as well
> reflow it to 80 columns.
I'll update this for the next version.
>
> > > */
> > > - 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;
> > > }
>
--
Regards,
Sakari Ailus
