Re: [linux-pm] Runtime PM discussion notes

[Tony Lindgren <tony@atomide.com>]

* Mark Brown <broonie@opensource.wolfsonmicro.com> [110711 04:21]:
> On Mon, Jul 11, 2011 at 04:14:24AM -0700, Tony Lindgren wrote:
> > * Mark Brown <broonie@opensource.wolfsonmicro.com> [110711 03:59]:
> 
> > > Right, but it can be interesting to tell the PMIC that we went into this
> > > mode.  Possibly cpuidle will end up doing this as a result of signals
> > > generated as the CPU core goes down, but at that point it's just s2ram
> > > by another name.
> 
> > All PMIC devices should be shut down when not in use, so I don't know
> > what else you would configure in the PMIC. Maybe you have something else
> > there to configure? Just curious what kind of mess you have to deal with
> > compared to the mess I need to deal with :)
> 
> The interesting bits are things like being able to kill lots of the SoC
> core supplies when the RAM is in retention mode - the CPU needs to go
> through its shutdown procedures.

I see. I've seen cases these are pre-programmed to the PMIC and then
automatically triggered based on some event like WFI.
 
> > Also, hitting deeper sleep states from idle is not same as suspend to ram.
> > With suspend to ram the system timer is killed while timers behave in a
> > normal way when hitting deeper sleep states from idle.
> 
> Actually, it just occurred to me that if we're waiting for a system
> timer and can hand that off to a suitable timer in the PMIC then we can
> do a suspend to RAM for the deep idle state from the hardware point of
> view.

Cool, it would be nice to have a Linux generic way for programming a
separate hardware wake-up timer. Not RTC, but some more accurate timer that
might be too slow to access for general purpose usage.

Regards,

Tony