Hi Laurent, On 06/09/2013 10:23 PM, Laurent Pinchart wrote: > Hi Sylwester, > > On Sunday 09 June 2013 21:41:37 Sylwester Nawrocki wrote: >> Hi All, >> >> This small patch set adds a function for removing all links at a media >> entity. I found out such a function is needed when media entites that >> belong to a single media device have drivers in different kernel modules. >> This means virtually all camera drivers, since sensors are separate >> modules from the host interface drivers. >> >> More details can be found at each patch's description. > > The patches look good to me. Thanks, I would push v3 upstream if everyone agrees. I think there is further work to be done, to allow the media entities race-free access to their parent media device and the graph mutex. For example, entity->parent->graph_mutex is needed to access entity->stream_count in a subdev driver, but for that it needs to be ensured that entity->parent doesn't change unexpectedly. >> The links removal from a media entity is rather strightforward, but when >> and where links should be created/removed is not immediately clear to me. >> >> I assumed that links should normally be created/removed when an entity >> is registered to its media device, with the graph mutex held. >> >> I'm open to opinions whether it's good or not and possibly suggestions >> on how those issues could be handled differently. > > It's a very good question. So far links were created at initialization time > and assumed to stay until the device gets torn down. Existing drivers thus > access the links without holding the graph mutex. > > An easy solution to fix race conditions at link creation time would be to take > the graph mutex in media_entity_create_link(). We will still have to fix > drivers to take the mutex when accessing links, I don't think there's a way > around that. We also need to precisely define what the graph mutex protects > and how drivers can access links and entities. This will become especially > important when the media controller framework will be used in DRM/KMS. I agree with that. Clear and documented semantics of the graph mutex is essential. And it all really seems required for proper subdevs hotplugging, deferred probing support etc. Regards, Sylwester -- 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
