Hi Guennadi, On Thursday 01 November 2012 16:01:59 Guennadi Liakhovetski wrote: > On Thu, 1 Nov 2012, Laurent Pinchart wrote: > > 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? Connection information is definitely required, but that doesn't mean we need to wait on groups independently. -- 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
