x86: quick TSC calibration, improve

- make sure the final TSC timestamp is reliable too

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

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 839070ba8465..6dab90f68515 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -317,6 +317,12 @@ 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
                  * times, and each MSB had many hits, so we never