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Subject[RFC patch 1/4] x86: TSC: define the PIT latch value separate
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/tsc.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

Index: linux-2.6/arch/x86/kernel/tsc.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/tsc.c
+++ linux-2.6/arch/x86/kernel/tsc.c
@@ -122,6 +122,10 @@ static u64 tsc_read_refs(u64 *pm, u64 *h
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
* Interrupt Timer and return the frequency of the TSC
@@ -144,8 +148,8 @@ static unsigned long pit_calibrate_tsc(v
* (LSB then MSB) to begin countdown.
*/
outb(0xb0, 0x43);
- outb((CLOCK_TICK_RATE / (1000 / 50)) & 0xff, 0x42);
- outb((CLOCK_TICK_RATE / (1000 / 50)) >> 8, 0x42);
+ outb(CAL_LATCH & 0xff, 0x42);
+ outb(CAL_LATCH >> 8, 0x42);

tsc = t1 = t2 = get_cycles();

@@ -166,18 +170,18 @@ static unsigned long pit_calibrate_tsc(v
/*
* 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
*
* If the maximum is 10 times larger than the minimum,
* 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;

/* Calculate the PIT value */
delta = t2 - t1;
- do_div(delta, 50);
+ do_div(delta, CAL_MS);
return delta;
}

--



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