From: Chris Bajumpaa <cbajumpa@or8.net>
This patch fixes a problem with the TSC failing on via686a/KX133
motherboards either reverting to using the pit or deadlocking the machine
alltogether under heavy load. (Specifically Abit KA7/KA7-100).
Message from the log:
Dec 18 18:20:37 grinder kernel: Losing too many ticks!
Dec 18 18:20:37 grinder kernel: TSC cannot be used as a timesource. (Are
you running with SpeedStep?)
Dec 18 18:20:37 grinder kernel: Falling back to a sane timesource.
The snippet of code that was missing from timer_tsc.c comes from
timer_pit.c.
arch/i386/kernel/timers/timer_tsc.c | 12 ++++++++++++
1 files changed, 12 insertions(+)
diff -puN arch/i386/kernel/timers/timer_tsc.c~via-tsc-fix arch/i386/kernel/timers/timer_tsc.c
--- 25/arch/i386/kernel/timers/timer_tsc.c~via-tsc-fix 2003-12-20 07:30:10.000000000 -0800
+++ 25-akpm/arch/i386/kernel/timers/timer_tsc.c 2003-12-20 07:30:10.000000000 -0800
@@ -183,6 +183,18 @@ static void mark_offset_tsc(void)
count = inb_p(PIT_CH0); /* read the latched count */
count |= inb(PIT_CH0) << 8;
+
+ /*
+ * VIA686a test code... reset the latch if count > max + 1
+ * from timer_pit.c - cjb
+ */
+ if (count > LATCH) {
+ outb_p(0x34, PIT_MODE);
+ outb_p(LATCH & 0xff, PIT_CH0);
+ outb(LATCH >> 8, PIT_CH0);
+ count = LATCH - 1;
+ }
+
spin_unlock(&i8253_lock);
if (pit_latch_buggy) {
_