]> git.openfabrics.org - ~shefty/rdma-dev.git/commitdiff
Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
authorLinus Torvalds <torvalds@linux-foundation.org>
Mon, 10 Aug 2009 18:11:40 +0000 (11:11 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Mon, 10 Aug 2009 18:11:40 +0000 (11:11 -0700)
* '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()

arch/x86/kernel/tsc.c

index 6e1a368d21d4d9214feda8eb6fcabe9c043708e1..71f4368b357edf2a47fd035349bfbcd8c595e882 100644 (file)
@@ -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");