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[Qemu-devel] [7168] hpet: Fix emulation of HPET_TN_SETVAL (Jan Kiszka)

From: Anthony Liguori
Subject: [Qemu-devel] [7168] hpet: Fix emulation of HPET_TN_SETVAL (Jan Kiszka)
Date: Fri, 17 Apr 2009 20:50:58 +0000

Revision: 7168
Author:   aliguori
Date:     2009-04-17 20:50:58 +0000 (Fri, 17 Apr 2009)
Log Message:
hpet: Fix emulation of HPET_TN_SETVAL (Jan Kiszka)

While Intel's spec is not that clear here, latest changes to Linux' HPET
code (commit c23e253e67c9d8a91a0ffa33c1f571a17f0a2403, "x86: hpet: stop
HPET_COUNTER when programming periodic mode") strongly suggest that
HPET_TN_SETVAL rather means: Set _both_ the comparator value and

With this patch applied, I'm again able to boot 2.6.30-rc kernels as
they no longer panic like this (which was due to the comparator
register remaining 0):

..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
..MP-BIOS bug: 8254 timer not connected to IO-APIC
...trying to set up timer (IRQ0) through the 8259A ...
..... (found apic 0 pin 2) ...
....... failed.
...trying to set up timer as Virtual Wire IRQ...
..... failed.
...trying to set up timer as ExtINT IRQ...
..... failed :(.
Kernel panic - not syncing: IO-APIC + timer doesn't work! [...]

Signed-off-by: Jan Kiszka <address@hidden>
Signed-off-by: Anthony Liguori <address@hidden>

Modified Paths:

Modified: trunk/hw/hpet.c
--- trunk/hw/hpet.c     2009-04-17 20:50:54 UTC (rev 7167)
+++ trunk/hw/hpet.c     2009-04-17 20:50:58 UTC (rev 7168)
@@ -411,7 +411,7 @@
                            (timer->config & HPET_TN_SETVAL))
                     timer->cmp = (timer->cmp & 0xffffffff00000000ULL)
                                   | new_val;
-                else {
+                if (timer_is_periodic(timer)) {
                      * FIXME: Clamp period to reasonable min value?
                      * Clamp period to reasonable max value

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