[PATCH 07/14] media: soc-camera: support deferred probing of clients

[Mark Brown]

On Wed, Apr 10, 2013 at 09:53:20PM +0800, Barry Song wrote:
> 2013/4/10 Guennadi Liakhovetski <g.liakhovetski at gmx.de>:

> >> what about another possible way:
> >> we let all host and i2c client driver probed in any order,

> > This cannot work, because some I2C devices, e.g. sensors, need a clock
> > signal from the camera interface to probe. Before the bridge driver has
> > completed its probing and registered a suitable clock source with the
> > v4l2-clk framework, sensors cannot be probed. And no, we don't want to
> > fake successful probing without actually being able to talk to the
> > hardware.

> i'd say same dependency also exists on ASoC.  a "fake" successful
> probing doesn't mean it should really begin to work if there is no
> external trigger source.  ASoC has successfully done that by a machine
> driver to connect all DAI.
> a way is we put all things ready in their places, finally we connect
> them together and launch the whole hardware flow.

In the ASoC case the idea is that drivers should probe as far as they
can with just the chip and then register with the core.  The machine
driver defers probing until all components have probed and then runs
through second stage initialisaton which pulls everything together.
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