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x86: TSC: define the PIT latch value separate

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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Thomas Gleixner
2008-09-04 15:18:44 +00:00
committed by Ingo Molnar
parent d210baf53b
commit cce3e05724
1 changed files with 9 additions and 5 deletions
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14
arch/x86/kernel/tsc.c
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@@ -122,6 +122,10 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet)
return ULLONG_MAX; return ULLONG_MAX;
} }
#define CAL_MS 50
#define CAL_LATCH (CLOCK_TICK_RATE / (1000 / CAL_MS))
#define CAL_PIT_LOOPS 5000
/* /*
* Try to calibrate the TSC against the Programmable * Try to calibrate the TSC against the Programmable
* Interrupt Timer and return the frequency of the TSC * Interrupt Timer and return the frequency of the TSC
@@ -144,8 +148,8 @@ static unsigned long pit_calibrate_tsc(void)
* (LSB then MSB) to begin countdown. * (LSB then MSB) to begin countdown.
*/ */
outb(0xb0, 0x43); outb(0xb0, 0x43);
outb((CLOCK_TICK_RATE / (1000 / 50)) & 0xff, 0x42); outb(CAL_LATCH & 0xff, 0x42);
outb((CLOCK_TICK_RATE / (1000 / 50)) >> 8, 0x42); outb(CAL_LATCH >> 8, 0x42);
tsc = t1 = t2 = get_cycles(); tsc = t1 = t2 = get_cycles();
@@ -166,18 +170,18 @@ static unsigned long pit_calibrate_tsc(void)
/* /*
* Sanity checks: * Sanity checks:
* *
* If we were not able to read the PIT more than 5000 * If we were not able to read the PIT more than PIT_MIN_LOOPS
* times, then we have been hit by a massive SMI * times, then we have been hit by a massive SMI
* *
* If the maximum is 10 times larger than the minimum, * If the maximum is 10 times larger than the minimum,
* then we got hit by an SMI as well. * then we got hit by an SMI as well.
*/ */
if (pitcnt < 5000 || tscmax > 10 * tscmin) if (pitcnt < CAL_PIT_LOOPS || tscmax > 10 * tscmin)
return ULONG_MAX; return ULONG_MAX;
/* Calculate the PIT value */ /* Calculate the PIT value */
delta = t2 - t1; delta = t2 - t1;
do_div(delta, 50); do_div(delta, CAL_MS);
return delta; return delta;
} }