Re: [PATCH RESEND] i2c/nomadik: runtime PM support

[Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>]

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On Thu, May 03, 2012 at 02:59:25PM +0200, Rafael J. Wysocki wrote:
> On Thursday, May 03, 2012, Linus Walleij wrote:

> > If *all* runtime_resume() hooks for *all* devices in the same power
> > domain are called at this time on the way up/down we get a major
> > overhead as our primary power domain is pretty big.

> FWIW, in the generic PM domains framework used on the sh7372 platform we have
> a need_restore flag whose meaning is whether or not to call .runtime_suspend()
> (or its domain-specific counterpart) when the domain is about to be powered
> off and .runtime_resume() when the device is resumed by the runtime PM
> framework.  Those two callbacks are meant to save and restore the device's
> state, respectively, and there are two more domain-specific callbacks,
> .stop() and .start() that (in the case of sh7372) manipiulate the devices'
> clocks.

> So, if pm_runtime_suspend() is called for a device, we first check if it's OK
> to call .stop() for it (according to PM QoS constraints), but we don't call
> .runtime_suspend() for it yet at this point.  Next, we check if it's OK to
> power off the domain containing the device (taking PM QoS constraints and
> subdomains into consideration) and if we decide to do that, we call
> .runtime_suspend() for the devices in the domain, but only those whose
> need_restore flags are unset.  Then, if pm_runtime_resume() is called for
> one of the devices, we check its need_restore flag and call .runtime_resume()
> for the device if the flag set and .start() is called subsequently.

This seems like a really useful idiom in general - might it be worth
supporting as a standard framework feature?

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