Re: [ANN] Meeting minutes of the Cambourne meeting

[Mark Brown <broonie@opensource.wolfsonmicro.com>]

On Tue, Aug 30, 2011 at 05:42:55PM +0200, Laurent Pinchart wrote:

> A dependency system is tempting but will be very complex to implement 
> properly, especially when faced with cyclic dependencies. For instance the 
> OMAP3 ISP driver requires the camera sensor device to be present to proceed, 
> and the camera sensor requires a clock provided by the OMAP3 ISP. To solve 
> this we need to probe the OMAP3 ISP first, have it register its clock devices, 
> and then wait until all sensors become available.

With composite devices like that where the borad has sufficient
interesting stuff on it representing the board itself as a device (this
is what ASoC does).

> A probe deferral system is probably simpler, but it will have its share of 
> problems as well. In the above example, if the sensor is probed first, the 
> driver can return -EAGAIN in the probe() method as the clock isn't available 
> yet (I'm not sure how to differentiate between "not available yet" and "not 
> present in the system" though). However, if the OMAP3 ISP is probed first, 
> returning -EAGAIN in its probe() method won't really help, as we need to 
> register the clock before waiting for the sensor.

Having a device for the camera subsystem as a whole breaks this loop as
the probe of that device triggers the overall system probe.