Re: [linux-pm] Runtime PM discussion notes

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

On Mon, Jul 11, 2011 at 02:58:12AM -0700, Tony Lindgren wrote:
> * Mark Brown <broonie@opensource.wolfsonmicro.com> [110708 21:01]:

> > At least the Nexus S doesn't implmeent any of the deep idle
> > infrastructure.  However, I'd expect that you can achieve some power
> > saving from entering system suspend as if *everything* is off then the
> > PMIC can be suspended which can enable additional power savings.  Unless
> > I'm missing something that'd be hard to hit with cpuidle only stuff.

> You should be able to hit the same states from idle no problem. At that
> point the only things on are memory in retention and some wake-up timer.
> Even the timer could be off if you have hardware wake-up events, but then
> system timer won't work the noral way naturally.

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.

> The only way power down everything in suspend to disk :) Most PMICs have
> some functionality always on so they can charge the battery when it's
> empty.

With some PMICs the truly always on functionality is *very* minimal and
doesn't include chargers, it can be pretty much limited to wake sources
(including power status changes which might start charging if power
appears).