Hi Mauro, On Thursday 16 September 2010 12:35:45 Mauro Carvalho Chehab wrote: > Em 16-09-2010 05:46, Laurent Pinchart escreveu: > > On Saturday 11 September 2010 22:38:33 Sakari Ailus wrote: > >> Mauro Carvalho Chehab wrote: > >>> Em 20-08-2010 12:29, Laurent Pinchart escreveu: > >>>> From: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx> > >>>> > >>>> Basically these are the interface functions: > >>>> > >>>> media_entity_get() - acquire entity > >>>> media_entity_put() - release entity > >>>> > >>>> If the entity is of node type, the power change is distributed to > >>>> all connected entities. For non-nodes it only affects that very > >>>> node. A mutex is used to serialise access to the entity graph. > >>>> > >>>> In the background there's a depth-first search algorithm that > >>>> traverses the active links in the graph. All these functions parse > >>>> the graph to implement whatever they're to do. > >>>> > >>>> The module counters are increased/decreased in media_entity_get/put to > >>>> prevent module unloading when an entity is referenced. > >>>> > >>>> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx> > >>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > >>>> Signed-off-by: Stanimir Varbanov <svarbanov@xxxxxxxxxx> > >>>> --- > >>>> > >>>> Documentation/media-framework.txt | 37 +++++++++ > >>>> drivers/media/media-device.c | 1 + > >>>> drivers/media/media-entity.c | 146 > >>>> +++++++++++++++++++++++++++++++++++++ include/media/media-device.h > >>>> > >>>> | 4 + > >>>> > >>>> include/media/media-entity.h | 15 ++++ > >>>> 5 files changed, 203 insertions(+), 0 deletions(-) > >>>> > >>>> diff --git a/Documentation/media-framework.txt > >>>> b/Documentation/media-framework.txt index a599824..59649e9 100644 > >>>> --- a/Documentation/media-framework.txt > >>>> +++ b/Documentation/media-framework.txt > >>>> @@ -278,3 +278,40 @@ When the graph traversal is complete the function > >>>> will return NULL. > >>>> > >>>> Graph traversal can be interrupted at any moment. No cleanup function > >>>> call is required and the graph structure can be freed normally. > >>>> > >>>> + > >>>> +Reference counting and power handling > >>>> +------------------------------------- > >>>> + > >>>> +Before accessing type-specific entities operations (such as the V4L2 > >>>> +sub-device operations), drivers must acquire a reference to the > >>>> entity. This +ensures that the entity will be powered on and ready to > >>>> accept requests. +Similarly, after being done with an entity, drivers > >>>> must release the +reference. > >>>> + > >>>> + media_entity_get(struct media_entity *entity) > >>>> + > >>>> +The function will increase the entity reference count. If the entity > >>>> is a node +(MEDIA_ENTITY_TYPE_NODE type), the reference count of all > >>>> entities it is +connected to, both directly or indirectly, through > >>>> active links is increased. +This ensures that the whole media > >>>> pipeline will be ready to process + > >>>> +Acquiring a reference to an entity increases the media device module > >>>> reference +count to prevent module unloading when an entity is being > >>>> used. + > >>>> +media_entity_get will return a pointer to the entity if successful, > >>>> or NULL +otherwise. > >>>> + > >>>> + media_entity_put(struct media_entity *entity) > >>>> + > >>>> +The function will decrease the entity reference count and, for node > >>>> entities, +like media_entity_get, the reference count of all connected > >>>> entities. Calling +media_entity_put with a NULL argument is valid and > >>>> will return immediately. + > >>>> +When the first reference to an entity is acquired, or the last > >>>> reference +released, the entity's set_power operation is called. > >>>> Entity drivers must +implement the operation if they need to perform > >>>> any power management task, +such as turning powers or clocks on or > >>>> off. If no power management is +required, drivers don't need to > >>>> provide a set_power operation. The operation +is allowed to fail when > >>>> turning power on, in which case the media_entity_get +function will > >>>> return NULL. > >>> > >>> The idea of doing power management via media entity get/put doesn't > >>> seem right. The mediabus interface and its usage should be optional, > >>> and only specialized applications will likely implement it. If a > >>> refcount 0 means power off, it ends that a device implementing the > >>> media bus will not work with V4L2 applications. > >> > >> The Media controller does handle the power through reference count but > >> this does not limit to subdev entities. The reference count is also > >> applied recursively to all entities which are connected through active > >> links. > >> > >> There are two cases: > >> > >> 1. The user application opens a subdev node. The subdev entity use count > >> will be incremented and the subdev will be powered up. > >> > >> 2. The user application opens a video node. The reference count for all > >> entities connected to the video node entity through active links will be > >> incremented. Subdevs will be powered up as well (if they are not already > >> because of (1) above). The same works if the entities connected through > >> a video node are connected to another entity and the link to that entity > >> is activated. In this case the use_counts of the entity sets are applied > >> across the both sets. > >> > >> The user application does not need to use the Media controller interface > >> to get this functionality. > > > > That's correct. The subdev s_power operation is still there and can be > > called directly by non-MC bridge drivers as required. > > It is clear that non-MC bridge devices will not be affected by MC. > > My concern is about MC bridge drivers. Userspace may not be implementing > MC. Yet, the device needs to fully work. If you're relying at MC to power > up parts of the device, this means that a pure V4L2 application won't work > anymore. > > I didn't see any patch on this series addressing this case. When the non-MC userspace application will open a video device node, the media_entity_get() call will power up all entities (subdevs in this case) in the pipeline, so it will be completely transparent for V4L2-only applications. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
