Hi Laurent, Thanks for the comments.
On Thu, Nov 15, 2012 at 01:46:23AM +0100, Laurent Pinchart wrote: > On Wednesday 14 November 2012 23:13:45 Sakari Ailus wrote: > > On Wed, Nov 14, 2012 at 10:23:19AM +0100, Sylwester Nawrocki wrote: > > > On 11/13/2012 03:24 PM, Sakari Ailus wrote: > > > > Hi all, > > > > > > > > Comments would be appreciated, either positive or negative. The omap3isp > > > > driver does the same check itself currently, but I think this is more > > > > generic than that. > > > > > > > > Thanks. > > > > > > > > On Fri, Oct 26, 2012 at 10:46:17PM +0300, Sakari Ailus wrote: > > > >> If an entity has sink pads, at least one of them must be connected to > > > >> another pad with an enabled link. If a driver with multiple sink pads > > > >> has more strict requirements the check should be done in the driver > > > >> itself. > > > >> > > > >> Just requiring one sink pad is connected with an enabled link is enough > > > >> API-wise: entities with sink pads with only disabled links should not > > > >> be allowed to stream in the first place, but also in a different > > > >> operation mode a device might require only one of its pads connected > > > >> with an active link. > > > >> > > > >> If an entity has an ability to function as a source entity another > > > >> logical entity connected to the aforementioned one should be used for > > > >> the purpose. > > > > > > Why not leave it to individual drivers ? I'm not sure if it is a good idea > > > not to allow an entity with sink pads to be used as a source only. It > > > might be appropriate for most of the cases but likely not all. I'm > > > inclined not to add this requirement in the API. Just my opinion though. > > > > I'm just wondering what would be the use case for that. > > > > What comes closest is generating a test pattern, but even that should be a > > separate subdev: the test pattern can be enabled by enabling the link from > > the test pattern generator subdev. > > That would force creating a separate subdev just to support test pattern > generation, I'm not sure if I want to push for that. There might also be > other The benefit of standard interfaces and uniform behaviour of those interfaces is that you can configure test pattern generation using e.g. media-ctl and yavta. Nothing else; not even private controls are needed. > use cases not related to V4L (thus the cross-posting). That's certainly possible. ... > > One opion I can think of is to call link_validate op of struct > > media_entity_operations also for disabled links on entities that are > > connected through active links (on V4L2 to a video node right before > > streaming, for example). > > > > That'd make it easy to perform the check in the drivers. > > > > What do you think? > > I think that would be a bit too complex. Drivers (or the V4L core) would need > to gather data from multiple links in some state object to find out if the > complete pipeline is valid or not. > > Another option would be to set a flag somewhere to indicate whether the check > should be performed by the media core or left to drivers. As different types > of drivers might need different types of checks, I think I would prefer for > now to walk the graph one more time in the OMAP3 ISP driver, as currently > done, and revisit this issue when we will have a couple of drivers > implementing pipeline validity checks. I'm just a bit uncomfortable adding > core code for a feature that has a single user at the moment without a clear > view regarding how it would scale. Honestly, I think that a driver that has configurable links but does not require this check to be done is quite probably broken. I'm not really convinced there is even a use case for a subdev operating its all sink pads disconnected. Btw. this "somewhere" could be struct media_pad. It already has a "flags" field. We could call it MEDIA_PAD_FL_MUST_CONNECT. -- Kind regards, Sakari Ailus e-mail: sakari.ai...@iki.fi XMPP: sai...@retiisi.org.uk _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
