Re: [linux-pm] Runtime PM discussion notes

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday, July 29, 2011, Pavel Machek wrote:
> Hi!
> 
> > > > 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.
> > > 
> > > Yep.  At LinuxCon Cambridge two years ago, we had a discussion about 
> > > whether it would be possible to enter ACPI S-states from CPUIdle (or some 
> > > idle governor) on Intel chips.  If I remember correctly, the conclusion 
> > > was that ACPI always disables the screen/backlight, so it would only be 
> > > useful for situations where that was acceptable.
> 
> Well, auto suspending when screensaver is active would still be
> useful.
> 
> (And IIRC some machines kept screen on when in S-state unless driver
> powered it down... but that might be S1.
> 
> > The reason why you can't enter ACPI S-states from CPUidle is because you
> > need to go out of the idle loop to execute some ACPI-specific stuff.  Which
> > is not even specific to Intel chips, but to ACPI in general.
> 
> The code was little tricky/unclean, but it "worked" for me at one
> point... I called it  "sleepy linux".

Yes, you can find a system where it might kind of work (just because
_PTS is empty or something like this).  Is it going to work in general?
No way.

So please let's turn into something at least _theoretically_ viable.

Thanks,
Rafael