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Commit 4637a74c authored by David P. Reed's avatar David P. Reed Committed by Andi Kleen
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[PATCH] x86-64: Avoid overflows during apic timer calibration 



- 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: default avatar <dpreed@reed.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 9d016dd4

arch/x86_64/kernel/apic.c

+6 −5
Original line number Diff line number Diff line
@@ -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);