On Thu, 1 Nov 2012, Hans Verkuil wrote: > On Thu November 1 2012 16:01:59 Guennadi Liakhovetski wrote: > > On Thu, 1 Nov 2012, Laurent Pinchart wrote: > > > > > Hello, > > > > > > On Monday 22 October 2012 17:22:16 Hans Verkuil wrote: > > > > On Mon October 22 2012 16:48:05 Guennadi Liakhovetski wrote: > > > > > On Mon, 22 Oct 2012, Hans Verkuil wrote: > > > > > > On Mon October 22 2012 14:50:14 Guennadi Liakhovetski wrote: > > > > > > > On Mon, 22 Oct 2012, Hans Verkuil wrote: > > > > > > > > On Mon October 22 2012 13:08:12 Guennadi Liakhovetski wrote: > > > > > > > > > On Mon, 22 Oct 2012, Hans Verkuil wrote: > > > > > > > > > > On Sat October 20 2012 00:20:24 Guennadi Liakhovetski wrote: > > > > > > > > > > > Currently bridge device drivers register devices for all > > > > > > > > > > > subdevices synchronously, tupically, during their probing. > > > > > > > > > > > E.g. if an I2C CMOS sensor is attached to a video bridge > > > > > > > > > > > device, the bridge driver will create an I2C device and wait > > > > > > > > > > > for the respective I2C driver to probe. This makes linking of > > > > > > > > > > > devices straight forward, but this approach cannot be used > > > > > > > > > > > with intrinsically asynchronous and unordered device > > > > > > > > > > > registration systems like the Flattened Device Tree. To > > > > > > > > > > > support such systems this patch adds an asynchronous subdevice > > > > > > > > > > > registration framework to V4L2. To use it respective (e.g. > > > > > > > > > > > I2C) subdevice drivers must request deferred probing as long > > > > > > > > > > > as their bridge driver hasn't probed. The bridge driver during > > > > > > > > > > > its probing submits a an arbitrary number of subdevice > > > > > > > > > > > descriptor groups to the framework to manage. After that it > > > > > > > > > > > can add callbacks to each of those groups to be called at > > > > > > > > > > > various stages during subdevice probing, e.g. after > > > > > > > > > > > completion. Then the bridge driver can request single groups > > > > > > > > > > > to be probed, finish its own probing and continue its video > > > > > > > > > > > subsystem configuration from its callbacks. > > > > > > > > > > > > > > > > > > > > What is the purpose of allowing multiple groups? > > > > > > > > > > > > > > > > > > To support, e.g. multiple sensors connected to a single bridge. > > > > > > > > > > > > > > > > So, isn't that one group with two sensor subdevs? > > > > > > > > > > > > > > No, one group consists of all subdevices, necessary to operate a > > > > > > > single video pipeline. A simple group only contains a sensor. More > > > > > > > complex groups can contain a CSI-2 interface, a line shifter, or > > > > > > > anything else. > > > > > > > > > > > > Why? Why would you want to wait for completion of multiple groups? You > > > > > > need all subdevs to be registered. If you split them up in multiple > > > > > > groups, then you have to wait until all those groups have completed, > > > > > > which only makes the bridge driver more complex. It adds nothing to the > > > > > > problem that we're trying to solve. > > > > > > > > > > I see it differently. Firstly, there's no waiting. > > > > > > > > If they are independent, then that's true. But in almost all cases you need > > > > them all. Even in cases where theoretically you can 'activate' groups > > > > independently, it doesn't add anything. It's overengineering, trying to > > > > solve a problem that doesn't exist. > > > > > > > > Just keep it simple, that's hard enough. > > > > > > I quite agree here. Sure, in theory groups could be interesting, allowing you > > > to start using part of the pipeline before everything is properly initialized, > > > or if a sensor can't be probed for some reason. In practice, however, I don't > > > think we'll get any substantial gain in real use cases. I propose dropping the > > > groups for now, and adding them later if we need to. > > > > Good, I need them now:-) These groups is what I map to /dev/video* nodes > > in soc-camera and what corresponds to struct soc_camera_device objects. > > > > We need a way to identify how many actual "cameras" (be it decoders, > > encoders, or whatever else end-devices) we have. And this information is > > directly related to instantiating subdevices. You need information about > > subdevices and their possible links - even if you use MC. You need to > > know, that sensor1 is connected to bridge interface1 and sensor2 can be > > connected to interfaces 2 and 3. Why do we want to handle this information > > separately, if it is logically connected to what we're dealing with here > > and handling it here is simple and natural? > > Because these are two separate problems. Determining which sensor is connected > to which bridge interface should be defined in the device tree and is reflected > in the topology reported by the media controller. None of this has anything to > do with the asynchronous subdev registration. Ok, maybe these two notions have to be separated more cleanly. Maybe it would be good to first introduce a notion of subdevice groups, then add notifiers for both - single subdevs and groups. > Your 'group' concept seems to be 1) very vague :-) I see it as a flexibility advantage;-) > and 2) specific to soc-camera. Not sure about this. I am trying to keep my abstractions within soc-camera, but if we want to implement notifiers and only limit ourselves to per-subdev ones, implementing groups on top of this in soc-camera would be ugly. > But even for soc-camera I don't see what advantage the group concept brings you > with respect to async registration. I tried to explain this above: it tells me when I can complete soc-camera device instantiation and create a video device node. For example, if on an sh-mobile system I have a parallel and a serial sensors, I would have two groups: group #1 would contain only the parallel sensor, group #2 would contain the serial sensor and the CSI2 interface. Whenever a group is reported as complete, I can instantiate an soc-camera device and register a video device node. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- 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
