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Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

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* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86: Fix serialization in pit_expect_msb()
This commit is contained in:
Linus Torvalds 2009-08-10 11:11:40 -07:00
commit a3263969b0
1 changed files with 22 additions and 7 deletions
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29
arch/x86/kernel/tsc.c
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@ -275,15 +275,20 @@ static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
* use the TSC value at the transitions to calculate a pretty
* good value for the TSC frequencty.
*/
static inline int pit_verify_msb(unsigned char val)
{
/* Ignore LSB */
inb(0x42);
return inb(0x42) == val;
}
static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
{
int count;
u64 tsc = 0;
for (count = 0; count < 50000; count++) {
/* Ignore LSB */
inb(0x42);
if (inb(0x42) != val)
if (!pit_verify_msb(val))
break;
tsc = get_cycles();
}
@ -336,8 +341,7 @@ static unsigned long quick_pit_calibrate(void)
* to do that is to just read back the 16-bit counter
* once from the PIT.
*/
inb(0x42);
inb(0x42);
pit_verify_msb(0);
if (pit_expect_msb(0xff, &tsc, &d1)) {
for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) {
@ -348,8 +352,19 @@ static unsigned long quick_pit_calibrate(void)
* Iterate until the error is less than 500 ppm
*/
delta -= tsc;
if (d1+d2 < delta >> 11)
goto success;
if (d1+d2 >= delta >> 11)
continue;
/*
* Check the PIT one more time to verify that
* all TSC reads were stable wrt the PIT.
*
* This also guarantees serialization of the
* last cycle read ('d2') in pit_expect_msb.
*/
if (!pit_verify_msb(0xfe - i))
break;
goto success;
}
}
printk("Fast TSC calibration failed\n");