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[PATCH] x86-64: Avoid overflows during apic timer calibration

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- Use 64bit TSC calculations to avoid handling overflow
- Use 32bit unsigned arithmetic for the APIC timer. This
way overflows are handled correctly.
- Fix exit check of loop to account for apic timer counting down

Signed-off-by: dpreed@reed.com
Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
David P. Reed 2007-05-02 19:27:20 +02:00 committed by Andi Kleen
parent 9d016dd43b
commit 4637a74cf2
1 changed files with 6 additions and 5 deletions
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11
arch/x86_64/kernel/apic.c
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@ -839,14 +839,15 @@ static void setup_APIC_timer(unsigned int clocks)
static int __init calibrate_APIC_clock(void)
{
int apic, apic_start, tsc, tsc_start;
unsigned apic, apic_start;
unsigned long tsc, tsc_start;
int result;
/*
* Put whatever arbitrary (but long enough) timeout
* value into the APIC clock, we just want to get the
* counter running for calibration.
*/
__setup_APIC_LVTT(1000000000);
__setup_APIC_LVTT(4000000000);
apic_start = apic_read(APIC_TMCCT);
#ifdef CONFIG_X86_PM_TIMER
@ -857,13 +858,13 @@ static int __init calibrate_APIC_clock(void)
} else
#endif
{
rdtscl(tsc_start);
rdtscll(tsc_start);
do {
apic = apic_read(APIC_TMCCT);
rdtscl(tsc);
rdtscll(tsc);
} while ((tsc - tsc_start) < TICK_COUNT &&
(apic - apic_start) < TICK_COUNT);
(apic_start - apic) < TICK_COUNT);
result = (apic_start - apic) * 1000L * tsc_khz /
(tsc - tsc_start);