Re: sysctl support for ICTC

Hi all,

Found something else re. power management...

On  12 Sep, this message from Benjamin Herrenschmidt echoed through cyberspace:

quoted

As an exercise ;-), I've added sysctl support for controlling and
displaying the contents of the G3 (and G4?) ICTC register.

Heh ! Nice ;) That's something I've wanted to do for years and never
ended up actually coding ;)

I know that feeling ;-))

quoted

So, managing ICTC could be part of an intelligent apmd-style daemon
specifically for PPC.

Well, I didn't think about that aspect of things with DPM.

The Darwin code has complete temperature control and uses the ICTC to
regulate it. That could be done from userland too on linux, by also
adding some support for the temp. registers.

Ah, temp registers. That's good, since IIRC there were a few atempts
long ago in this place to add temperature monitoring, but none ever
ended up with something useful. Finally, that 0 in the cpuinfo could be
replaced with something meaningful ;-)

Now, about conserving power on portable machines, there's another thing.
In the idle task, the processor (if supporting sleep) is put to either
NAP or DOZE mode (see arch/ppc/kernel/idle.c). NAP mode seems to save
more power, but there's no snooping. Don't know whether that would be a
problem... but I guess it could. Anyway, if somebody wants to
experiment, NAP can be enabled with
/proc/sys/kernel/powersave-nap.

Also, if the G4 supports power management, its PVR should be added to
power_save() in arch/ppc/kernel/idle.c, in preparation for G4 Powerbooks
;-)

Michel

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