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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:
    > > DISPLAY_BLANK off
    > > 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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