x86: TSC: define the PIT latch value separate
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 346cae5..aa11413 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -122,6 +122,10 @@
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 @@
* (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 @@
/*
* 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;
}