x86: quick TSC calibration, improve

- make sure the final TSC timestamp is reliable too

Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 839070ba8465bc589aea211946755d695fb0c78d..6dab90f68515a573e710415c038b7b8c32daf9a5 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -316,6 +316,12 @@ static unsigned long quick_pit_calibrate(void)
                }
                t2 = get_cycles();
 
+               /*
+                * Make sure we can rely on the second TSC timestamp:
+                */
+               if (!pit_expect_msb(--expect))
+                       goto failed;
+
                /*
                 * Ok, if we get here, then we've seen the
                 * MSB of the PIT decrement QUICK_PIT_ITERATIONS