Re: [linux-pm] Runtime PM discussion notes

[Mark Brown <broonie@opensource.wolfsonmicro.com>]

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.

> 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.