Em Thu, 17 Mar 2016 13:50:53 +0200
Sakari Ailus <sakari.ailus@xxxxxx> escreveu:
> Hi Mauro,
>
> On Wed, Mar 16, 2016 at 09:04:05AM -0300, Mauro Carvalho Chehab wrote:
> > Now that the media_device can be used by multiple drivers,
> > via devres, we need to be sure that it will be dropped only
> > when all drivers stop using it.
>
> Not long ago we split media device initialisation and registration into two.
> The intent with that was to prevent users from seeing the media device until
> all the initialisation is finished. I suppose that with dynamic updates, or
> media device being shared with two drivers, it might be difficult to achieve
> that. At least the method has to be different.
>
> media_device_init() and media_device_cleanup() were a pair where the latter
> undid the first.
Yes, this patch breaks the balance of _init()/_cleanup(), but this is for
a greater good. It is very hard to remove the devnode and cleanup the
media_device struct when multiple drivers can use it. The best way to
warrant that we'll be doing that is via kref.
> This patchs remove the requirement of calling cleanup
> explitly, breaking that model. It's perhaps not a big problem, there is
> likely no single driver which would initialise the media controller device
> once but would register and unregister it multiple times. I still wonder if
> we really lost something important if we removed media_device_init() and
> media_device_cleanup() altogether and merged the functionality in
> media_device_{,un}register().
>
> Cc Javier who wrote the patch.
That patch was written to avoid a race trouble of having the media
devnode to initialize too early. Merging them back would cause troubles.
Maybe what we could do, instead, is to rename media_device_init()
to media_device_register(), and call the function that creates the
devnode as media_device_create_devnode().
What do you think?
>
> commit 9832e155f1ed3030fdfaa19e72c06472dc2ecb1d
> Author: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
> Date: Fri Dec 11 20:57:08 2015 -0200
>
> [media] media-device: split media initialization and registration
>
> For system-wide media device, I think we'd need to introduce a new concept,
> graph, that would define an interconnected set of entities. This would
> mainly be needed for callbacks, e.g. the power on / off sequences of the
> entities could be specific to V4L as discussed earlier. With this approach
> hacks wouldn't be needed to be made in the first place to support two drivers
> sharing a media device.
>
> What was the original reason you needed to share the media device btw.?
>
> >
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
> > ---
> > drivers/media/media-device.c | 48 +++++++++++++++++++++++++++++++-------------
> > include/media/media-device.h | 3 +++
> > 2 files changed, 37 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> > index c32fa15cc76e..38e6c319fe6e 100644
> > --- a/drivers/media/media-device.c
> > +++ b/drivers/media/media-device.c
> > @@ -721,6 +721,15 @@ int __must_check __media_device_register(struct media_device *mdev,
> > {
> > int ret;
> >
> > + /* Check if mdev was ever registered at all */
> > + mutex_lock(&mdev->graph_mutex);
> > + if (media_devnode_is_registered(&mdev->devnode)) {
> > + kref_get(&mdev->kref);
> > + mutex_unlock(&mdev->graph_mutex);
> > + return 0;
> > + }
> > + kref_init(&mdev->kref);
> > +
> > /* Register the device node. */
> > mdev->devnode.fops = &media_device_fops;
> > mdev->devnode.parent = mdev->dev;
> > @@ -730,8 +739,10 @@ int __must_check __media_device_register(struct media_device *mdev,
> > mdev->topology_version = 0;
> >
> > ret = media_devnode_register(&mdev->devnode, owner);
> > - if (ret < 0)
> > + if (ret < 0) {
> > + media_devnode_unregister(&mdev->devnode);
> > return ret;
> > + }
> >
> > ret = device_create_file(&mdev->devnode.dev, &dev_attr_model);
> > if (ret < 0) {
> > @@ -739,6 +750,7 @@ int __must_check __media_device_register(struct media_device *mdev,
> > return ret;
> > }
> >
> > + mutex_unlock(&mdev->graph_mutex);
> > dev_dbg(mdev->dev, "Media device registered\n");
> >
> > return 0;
> > @@ -773,23 +785,15 @@ void media_device_unregister_entity_notify(struct media_device *mdev,
> > }
> > EXPORT_SYMBOL_GPL(media_device_unregister_entity_notify);
> >
> > -void media_device_unregister(struct media_device *mdev)
> > +static void do_media_device_unregister(struct kref *kref)
> > {
> > + struct media_device *mdev;
> > struct media_entity *entity;
> > struct media_entity *next;
> > struct media_interface *intf, *tmp_intf;
> > struct media_entity_notify *notify, *nextp;
> >
> > - if (mdev == NULL)
> > - return;
> > -
> > - mutex_lock(&mdev->graph_mutex);
> > -
> > - /* Check if mdev was ever registered at all */
> > - if (!media_devnode_is_registered(&mdev->devnode)) {
> > - mutex_unlock(&mdev->graph_mutex);
> > - return;
> > - }
> > + mdev = container_of(kref, struct media_device, kref);
> >
> > /* Remove all entities from the media device */
> > list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
> > @@ -807,13 +811,26 @@ void media_device_unregister(struct media_device *mdev)
> > kfree(intf);
> > }
> >
> > - mutex_unlock(&mdev->graph_mutex);
> > + /* Check if mdev devnode was registered */
> > + if (!media_devnode_is_registered(&mdev->devnode))
> > + return;
> >
> > device_remove_file(&mdev->devnode.dev, &dev_attr_model);
> > media_devnode_unregister(&mdev->devnode);
> >
> > dev_dbg(mdev->dev, "Media device unregistered\n");
> > }
> > +
> > +void media_device_unregister(struct media_device *mdev)
> > +{
> > + if (mdev == NULL)
> > + return;
> > +
> > + mutex_lock(&mdev->graph_mutex);
> > + kref_put(&mdev->kref, do_media_device_unregister);
> > + mutex_unlock(&mdev->graph_mutex);
> > +
> > +}
> > EXPORT_SYMBOL_GPL(media_device_unregister);
> >
> > static void media_device_release_devres(struct device *dev, void *res)
> > @@ -825,13 +842,16 @@ struct media_device *media_device_get_devres(struct device *dev)
> > struct media_device *mdev;
> >
> > mdev = devres_find(dev, media_device_release_devres, NULL, NULL);
> > - if (mdev)
> > + if (mdev) {
> > + kref_get(&mdev->kref);
> > return mdev;
> > + }
> >
> > mdev = devres_alloc(media_device_release_devres,
> > sizeof(struct media_device), GFP_KERNEL);
> > if (!mdev)
> > return NULL;
> > +
> > return devres_get(dev, mdev, NULL, NULL);
> > }
> > EXPORT_SYMBOL_GPL(media_device_get_devres);
> > diff --git a/include/media/media-device.h b/include/media/media-device.h
> > index ca3871b853ba..73c16e6e6b6b 100644
> > --- a/include/media/media-device.h
> > +++ b/include/media/media-device.h
> > @@ -23,6 +23,7 @@
> > #ifndef _MEDIA_DEVICE_H
> > #define _MEDIA_DEVICE_H
> >
> > +#include <linux/kref.h>
> > #include <linux/list.h>
> > #include <linux/mutex.h>
> >
> > @@ -283,6 +284,7 @@ struct media_entity_notify {
> > * struct media_device - Media device
> > * @dev: Parent device
> > * @devnode: Media device node
> > + * @kref: Object refcount
> > * @driver_name: Optional device driver name. If not set, calls to
> > * %MEDIA_IOC_DEVICE_INFO will return dev->driver->name.
> > * This is needed for USB drivers for example, as otherwise
> > @@ -347,6 +349,7 @@ struct media_device {
> > /* dev->driver_data points to this struct. */
> > struct device *dev;
> > struct media_devnode devnode;
> > + struct kref kref;
> >
> > char model[32];
> > char driver_name[32];
> > --
> > 2.5.0
> >
>
--
Thanks,
Mauro
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