Re: [ANN] Meeting minutes of the Cambourne meeting

[Guennadi Liakhovetski <g.liakhovetski-Mmb7MZpHnFY@public.gmane.org>]

On Tue, 30 Aug 2011, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Tuesday 30 August 2011 00:20:09 Guennadi Liakhovetski wrote:
> > On Mon, 29 Aug 2011, Laurent Pinchart wrote:
> > 
> > [snip]
> > 
> > > My idea was to let the kernel register all devices based on the DT or
> > > board code. When the V4L2 host/bridge driver gets registered, it will
> > > then call a V4L2 core function with a list of subdevs it needs. The V4L2
> > > core would store that information and react to bus notifier events to
> > > notify the V4L2 host/bridge driver when all subdevs are present. At that
> > > point the host/bridge driver will get hold of all the subdevs and call
> > > (probably through the V4L2 core) their .registered operation. That's
> > > where the subdevs will get access to their clock using clk_get().
> > 
> > Correct me, if I'm wrong, but this seems to be the case of sensor (and
> > other i2c-client) drivers having to succeed their probe() methods without
> > being able to actually access the hardware?
> 
> That's right. I'd love to find a better way :-) Note that this is already the 
> case for many subdev drivers that probe the hardware in the .registered() 
> operation instead of the probe() method.

Then why do you think it is better, than adding devices from bridge 
drivers? Think about hotpluggable devices - drivers create devices all the 
time - USB etc. Why cannot we do the same? As a historic reference: 
soc-camera used to do this too before - probe without hardware access and 
"really-probe" after the host turns on the clock. Then we switched to 
registering devices later. I like the present approach better.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/