Re: [linux-pm] Runtime PM discussion notes

[Pavel Machek <pavel@ucw.cz>]

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".
								Pavel
-- 
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