Re: nokia 770 [was Re: community PM requirements/issues and PowerOP]

Pavel Machek
2006-12-13T21:58:31Z

On Thu 2006-12-14 00:56:24, Eugeny S. Mints wrote:
> David Brownell wrote:
> >On Wednesday 13 December 2006 1:03 pm, Pavel Machek wrote:
> >>On Wed 2006-12-13 15:12:07, Eugeny S. Mints wrote:
> >>>David Brownell wrote:
> >>>>On Tuesday 19 September 2006 11:25 am, Pavel Machek wrote:
> >>>>>Could you perhaps provide list of operating points for 770? It would
> >>>>>help understanding a bit, I'd say.
> >>>>If there was a followup here, I missed it ...
> >>>>
> >>>>ISTR that it doesn't use (formal) operating points, and that a lot of
> >>>>the
> >>>>basic SOC power savings (vs powering off the display or wifi) come from
> >>>>a
> >>>>different kind of mechanism entirely. Namely, a combination of dynamic
> >>>>tick with a modified system idle task, which enters one of the OMAP low
> >>>>power modes during those long periods between clock ticks or other irqs.
> >>>>
> >>>>That's one of the standard power saving schemes used on OMAP1 platforms
> >>>>with Linux.
> >>>sample of reasonable operating points for OMAP1 platforms along with
> >>>appropriate patches may be found at
> >>>http://dynamicpower.sourceforge.net/dpm-omap.html
> >
> >That's the old DPM stuff not any of the newer proposals right?
> >
> >I thought the question was specifically what N770 used.
> >
> >
> >>Okay... so you have system with 4 different cpu speeds. That should be
> >>simple enough to get running using cpufreq, no need for complex
> >>operating points patches.
> >
> >And OMAP1 does have cpufreq support. I believe that if I checked it out
> >I'd find that it's used on N770, as a good way to kick in low voltage
> >operation modes.
> >
> >... that's in addition to the reduced power idle, which didn't seem to
> >fit into the DPM framework in any obvious way.
> It fits. Omitting some details DPM allows to map/stick operating point to
> tasks. Mapping one of OMAP low power mode operating point to idle task does
> the job.

That's what I call a hack.

Take a look at acpi C1..C3 state on i386. They provide same
functionality ("reduced power idle"), but they are implemented in
reasonable way and already merged.
Pavel
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