notebook freezes
Bruce Evans
bde at zeta.org.au
Sun Mar 4 12:27:52 UTC 2007
On Fri, 2 Mar 2007, Stefan Ehmann wrote:
> On Thursday 01 March 2007 16:12, Stefan Ehmann wrote:
>> My few days old -current freezes if I press Fn-F6 (this is the combination
>> to adjust display brightness) if I've done a suspend/resume before.
>> Directly after boot it works fine.
> ...
> So I did a binary search.
>
> src/sys/i386/isa/clock.c r1.231 causes my notebook to freeze.
>
> Reverting this change in a CURRENT from today fixes the problem.
>
> The notebook is still pingable in this state. I experienced some other random
> hangs recently but don't know yet if those are related.
Oops. If suspend/resume clobbers the RTC state (which we already have code
to restore), then it can clobber the RTC index (which even the restoral code
assumes is unclobbered). Try this fix.
%%%
Index: clock.c
===================================================================
RCS file: /home/ncvs/src/sys/i386/isa/clock.c,v
retrieving revision 1.234
diff -u -2 -r1.234 clock.c
--- clock.c 4 Mar 2007 04:55:19 -0000 1.234
+++ clock.c 4 Mar 2007 11:58:00 -0000
@@ -580,4 +582,5 @@
/* Restore all of the RTC's "status" (actually, control) registers. */
/* XXX locking is needed for RTC access. */
+ rtc_reg = -1;
writertc(RTC_STATUSB, RTCSB_24HR);
writertc(RTC_STATUSA, rtc_statusa);
%%%
A similar fix might be needed for amd64, but amd64 doesn't have a resume
hook for putting it in. The RTC index might get clobbered even if the
data registers aren't.
I don't know how any of this works with ACPI. AFAIK (not far), the resume
hook is only called for APM.
I think the resume hook is not actually called on your system since
it would fix up the RTC index as a side effect of accessing 2 different
RTC registers. At worst, if it is called then it might do the following:
- write garbage to the current RTC register, and fail to mask interrupts.
This only happens if on resume rtc_reg is RTC_STATUSB but the physical
index is different. If RTC interrupts are used (which is normal if
ACPI timer interrups are not used), then rtc_reg is normally RTC_INTR
so there is no problem. Otherwise, there might be no problem because
the last RTC access might be to RTC_YEAR for inittodr().
- write the correct value to RTC_STATUSA, but lose if the RTC interrupt
disabling in the previous access was critical.
- write the correct value to RTC_STATUSB.
disabling in the previous access was critical, and end up with a
consistent index.
Bruce
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