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SubjectRe: 2.4.22 APM problems with IBM Thinkpad's
Ruben Puettmann writes:
> On Wed, Aug 13, 2003 at 03:13:02PM +0200, Mikael Pettersson wrote:
> >
> > This sounds like a well-known APM/local-APIC clash.
> nice to know ...
> >
> > Never ever use DISPLAY_BLANK if you also have SMP or UP_APIC.
> not nice so ;-( how is it with acpi? Same problem?
> > With APIC support enabled (SMP or UP_APIC), APM must be constrained:
> > CPU_IDLE off
> > built-in driver, not module
> Why will this not be disabled in make *config so that nobody will run in
> this problem?
> > This is because the apm driver does BIOS calls, and many BIOSen
> > (including the code in graphics cards, e.g. all Radeons it seems)
> > like to hang if a local APIC timer interrupt arrives.

Several reasons:
- The interaction wasn't understood initially, and some problems
didn't start appearing until late last year. The problems are
also system & configuration dependent.
Case in point #1: my P3B-F and P4T-E ASUS mainboards never had
problems until they started running 2.5 kernels, where HZ==1000
greatly increased the likelihood of a local APIC timer interrupt
while in BIOS screen blanking code.
Case in point #2: my TUSL2-C ASUS mobo (RIP) worked great until
I switched from a Millenium to a Radeon 8500, and found that it
hung because of local APIC timer interrupts while in BIOS screen
blanking code, even in 2.4 kernels.
- Fixing the APM driver would require that someone who understands
it modifies it to avoid BIOS calls (other than suspend/resume) when
UP_APIC is active. I'm not that person.
- The problems can be worked around by avoiding misconfigurations.
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