Re: [PATCH, RFC] [1/3] Generic in-kernel AC status

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

On Tuesday 14 February 2006 18:44, Thomas Renninger wrote:
> Pavel Machek wrote:
> > On Pá 10-02-06 09:06:43, Stefan Seyfried wrote:
> >> On Wed, Feb 08, 2006 at 12:57:53PM +0000, Matthew Garrett wrote:
> >>> The included patch adds support for power management methods to register 
> >>> callbacks in order to allow drivers to check if the system is on AC or 
> >>> not. Following patches add support to ACPI and APM. Feedback welcome.
> >> Ok. Maybe i am not seeing the point. But why do we need this in the kernel?
> >> Can't we handles this easily in userspace?
> > 
> > Some kernel parts need to now: for example powernow-k8: some
> > frequencies are not allowed when you are running off battery. [Just
> > now it is solved by not allowing those frequencies at all unless ACPI
> > is available; quite an ugly solution.]
> > 
> Allowed CPUfreqs are exported via _PPC.
> This is why a lot hardware sends an ac_adapter and a processor event
> when (un)plugging ac adapter.
> Limiting cpufreq already works nice that way.
> 
> AMD64 laptops are booting with lower freqs per default until they are
> pushed up, so there shouldn't be anything critical?

This is not true as far as my box is concerned (Asus L5D).  It starts with
the _highest_ clock available.

> For the brightness part, I don't see any "laptop is going to explode"
> issue.
> I always hated the brightness going down when I unplugged ac on M$

Currently I have the same problem on Linux, but I don't know the solution
(yet).  Any hints? :-)

Rafael
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