On 12/11/2015 03:57 PM, Javier Martinez Canillas wrote:
> Most media functions that unregister, check if the corresponding register
> function succeed before. So these functions can safely be called even if a
> registration was never made or the component as already been unregistered.
>
> Add the same check to media_device_unregister() function for consistency.
>
> This will also allow to split the media_device_register() function in an
> initialization and registration functions without the need to change the
> generic cleanup functions and error code paths for all the media drivers.
>
> Suggested-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
> Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
>
> ---
>
> Changes in v5: None
> Changes in v4: None
> Changes in v3: None
> Changes in v2:
> - Reword the documentation for media_device_unregister(). Suggested by Sakari.
> - Added Sakari's Acked-by tag for patch #1.
>
> drivers/media/media-device.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index c12481c753a0..11c1c7383361 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -577,6 +577,8 @@ EXPORT_SYMBOL_GPL(__media_device_register);
> * media_device_unregister - unregister a media device
> * @mdev: The media device
> *
> + * It is safe to call this function on an unregistered
> + * (but initialised) media device.
> */
> void media_device_unregister(struct media_device *mdev)
> {
> @@ -584,6 +586,10 @@ void media_device_unregister(struct media_device *mdev)
> struct media_entity *next;
> struct media_interface *intf, *tmp_intf;
>
> + /* Check if mdev was ever registered at all */
> + if (!media_devnode_is_registered(&mdev->devnode))
> + return;
This is a good check, however, this check will not prevent
media_device_unregister() from getting run twice by two
different drivers. i.e media_devnode gets unregistered
towards the end of at the end of media_device_unregister().
In an example case, if bridge driver and snd-usb-aduio both
call media_device_unregister(), this check won't help prevent
media_device_unregister() being done only once. I think we
need a different state variable in struct media_device
to ensure unregister is done only once.
> +
> /* Remove all entities from the media device */
> list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
> media_device_unregister_entity(entity);
>
--
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@xxxxxxxxxxxxxxx | (970) 217-8978
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