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authorLinus Torvalds <torvalds@linux-foundation.org>2009-08-10 11:11:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-08-10 11:11:40 -0700
commita3263969b02260f8733940f580c7af1c716d38ad (patch)
tree19dbddd4cf73c16903256d2196e51a28613a9c09
parent9b8f013a8361b05edf511f04fe93b36310b73806 (diff)
parentb6e61eef4f9f94714ac3ee4a5c96862d9bcd1836 (diff)
downloadconfigs-a3263969b02260f8733940f580c7af1c716d38ad.tar.gz
Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* '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()
-rw-r--r--arch/x86/kernel/tsc.c29
1 files changed, 22 insertions, 7 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 6e1a368d21d..71f4368b357 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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");