[PATCH] Validate PM-Timer rate at boot time
Add a check to the PM-Timer initialization code. It validates the PM-Timer rate against PIT channel 2 and rejects the PM-Timer if its rate is not withing 5% of the expected number. Rationale: The PMTMR timers of certain (older) mainboards are running at invalid rates, often much faster than the rate expected by the PM-Timer code. This causes the system clock to run much too fast. See also http://bugme.osdl.org/show_bug.cgi?id=2375 Possible workarounds are disabling the PM-Timer in the kernel config or disabling the PM-Timer at boot time through the "clock=tsc" parameter. However, we believe it is more user friendly to automatically validate the PM-Timer rate at boot time before using it as the system time source. Tested by me (with broken timer) and John Stultz (with good timer) and believed to be ok. Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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