sysctl support for ICTC

[Michel Lanners]

Hi all,

Found something else re. power management...

On  12 Sep, this message from Benjamin Herrenschmidt echoed through cyberspace:
>>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 ;-))

>>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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