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

["Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>]

On Thursday, May 03, 2012, Mark Brown wrote:
> 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?

The generic PM domains framework does this, it's not platform-specific
(if I understood your question correctly).

Thanks,
Rafael