Re: [Ksummit-discuss] [TECH TOPIC] PM dependencies

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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Hi Mark,

On Monday 12 May 2014 21:14:38 Mark Brown wrote:
> On Mon, May 12, 2014 at 07:43:22PM +0200, Laurent Pinchart wrote:
> > The problem is not limited to IOMMUs. We have similar dependencies at
> > suspend/resume time with camera interfaces for instance, where two
> > completely unrelated device in the Linux device hierarchy (a camera
> > interface platform device in the SoC and an I2C camera sensor) need to be
> > suspended and resumed in a controlled order. I'm sure many more use cases
> > exist.
> > 
> > Whether we can (partly) reuse existing infrastructure for this is not
> > clear. I'd like to gather use cases, to first find out exactly how
> > widespread the need is, and whether we can come up with a common solution
> > or we are really faced with different classes of similarly looking but
> > distinct issues.
>
> This is something ASoC has been resolving since forever with the machine
> drivers, Russell King recently created a generic version of the code
> that does the dependency deferral glue (see linux/component.h).  It's
> not a model of elegance but it ends up getting the job done.

That solves the probe time dependencies, but unfortunately not the runtime PM 
dependencies.

> Anyway, I'm definitely interested in this - a couple of the subsystems I
> maintain are affected and it's something I've thought about a bit.

-- 
Regards,

Laurent Pinchart

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