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SubjectRe: [ACPI] Re: PROBLEM: ACPI freezes 2.6.1 on boot
Linus Torvalds writes:
>
>
> On Thu, 22 Jan 2004, Mikael Pettersson wrote:
>
> > Karol Kozimor writes:
> > >
> > > diff -Bru linux-2.6.0-test8/arch/i386/kernel/apic.c patched/arch/i386/kernel/apic.c
> > > --- linux-2.6.0-test8/arch/i386/kernel/apic.c 2003-10-18 05:43:36.000000000 +0800
> > > +++ patched/arch/i386/kernel/apic.c 2003-10-30 23:17:50.000000000 +0800
> > > @@ -836,8 +836,8 @@
> > > {
> > > unsigned int lvtt1_value, tmp_value;
> > >
> > > - lvtt1_value = SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV) |
> > > - APIC_LVT_TIMER_PERIODIC | LOCAL_TIMER_VECTOR;
> > > + lvtt1_value = APIC_LVT_TIMER_PERIODIC | LOCAL_TIMER_VECTOR;
> > > +
> > > apic_write_around(APIC_LVTT, lvtt1_value);
> >
> > What is the purpose of this change?
> > I don't remember seeing this before on LKML. (I don't have time to read bugzilla.)
>
> Hmm.. It does seem to fix things for a couple of people, so it looks
> interesting.
>
> As far as I can tell, the _only_ thing it does is to change the timer base
> from "DIV" to "CLKIN". I seem to have misplaced my ia-32 "volume 3" thing,
> but I have an old one for a pentium, and that one doesn't actually
> haev the timer-base thing at all - and marks those bits as "reserved".
>
> So it is entirely possible that the only safe value to write there is 0.

Confirmed. Those bits (18 and 19 in LVTT) are marked reserved in the
latest IA32 Volume 3. I have no idea where this APIC_TIMER_BASE came
from (maybe some ancient discrete LAPIC thing?), but we almost certainly
shouldn't write anything but zero to them.

> So I'm inclined to apply the patch, but it would be better if somebody who

I agree. The patch should be applied.

/Mikael
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