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()
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a3263969b0
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@ -275,15 +275,20 @@ static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
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* use the TSC value at the transitions to calculate a pretty
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* good value for the TSC frequencty.
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*/
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static inline int pit_verify_msb(unsigned char val)
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{
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/* Ignore LSB */
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inb(0x42);
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return inb(0x42) == val;
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}
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static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
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{
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int count;
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u64 tsc = 0;
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for (count = 0; count < 50000; count++) {
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/* Ignore LSB */
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inb(0x42);
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if (inb(0x42) != val)
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if (!pit_verify_msb(val))
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break;
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tsc = get_cycles();
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}
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@ -336,8 +341,7 @@ static unsigned long quick_pit_calibrate(void)
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* to do that is to just read back the 16-bit counter
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* once from the PIT.
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*/
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inb(0x42);
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inb(0x42);
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pit_verify_msb(0);
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if (pit_expect_msb(0xff, &tsc, &d1)) {
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for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) {
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@ -348,8 +352,19 @@ static unsigned long quick_pit_calibrate(void)
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* Iterate until the error is less than 500 ppm
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*/
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delta -= tsc;
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if (d1+d2 < delta >> 11)
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goto success;
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if (d1+d2 >= delta >> 11)
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continue;
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/*
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* Check the PIT one more time to verify that
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* all TSC reads were stable wrt the PIT.
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*
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* This also guarantees serialization of the
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* last cycle read ('d2') in pit_expect_msb.
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*/
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if (!pit_verify_msb(0xfe - i))
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break;
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goto success;
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}
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}
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printk("Fast TSC calibration failed\n");
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