Re: power management on laptops
From: Michal Jaegermann (michal_at_gortel.phys.ualberta.ca)
Date: Thu, 5 May 2005 18:21:49 +0000 (UTC)
Michael Perry <firstname.lastname@example.org> wrote:
> APM on the other hand usually just works.
Life would be too beatifull if that "usually" did not really translate
to "sometimes, it depends".
Even if a laptop does have one or both of APM and ACPI it does not mean
that one of these, or both as the case may be, is not horribly broken.
I have seen various cases. These functions are supplied by BIOS and you
are basically at a mercy of a BIOS writer. On the top of it these
functions often turn off interrupts for very long periods and, as you
can guess, kernel does not like that at all. Sometimes a BIOS update
may help, if something like that is available, but cases when things got
worse after such update are not unheard of. Linux also may have bugs,
or workarounds which really help only with some models and turn out to
be harmfull elsewhere, and this compounds the problem. ACPI interfaces
are here indeed more likely candidates.
ACPI is a complex beast and there are good chances that BIOS got it
wrong but that does not mean that APM if fine - especially with newer
laptops. There are laptops where one of these is rougly sane. If
you have one of these then enjoy.
BTW - I heard about laptops which will not even boot without an ACPI
support turned on and these two approaches to a power managment are