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[Qemu-devel] [PATCH][STABLE] hpet: Fix emulation of HPET_TN_SETVAL

From: Jan Kiszka
Subject: [Qemu-devel] [PATCH][STABLE] hpet: Fix emulation of HPET_TN_SETVAL
Date: Thu, 16 Apr 2009 22:08:03 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

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>

 hw/hpet.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/hw/hpet.c b/hw/hpet.c
index 7df2d05..c7945ec 100644
--- a/hw/hpet.c
+++ b/hw/hpet.c
@@ -411,7 +411,7 @@ static void hpet_ram_writel(void *opaque, 
target_phys_addr_t addr,
                            (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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