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x86: restrict PIT clocksource usage 

PIT clocksource is registered unconditionally even when HPET is enabled
or when PIT is replaced by the local APIC timer. In both cases PIT can
not be used as it is stopped and the readout would be stale.

Prevent registering PIT in those cases.

patch depends on:

  x86: offer is_hpet_enabled() on !CONFIG_HPET_TIMER too

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Thomas Gleixner 2008-01-30 13:30:02 +01:00 committed by Ingo Molnar
parent df619e6baf
commit 316da3b3fc
1 changed files with 9 additions and 1 deletions
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10
arch/x86/kernel/i8253.c
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@ -197,7 +197,15 @@ static struct clocksource clocksource_pit = {
static int __init init_pit_clocksource(void)
{
if (num_possible_cpus() > 1) /* PIT does not scale! */
/*
* Several reasons not to register PIT as a clocksource:
*
* - On SMP PIT does not scale due to i8253_lock
* - when HPET is enabled
* - when local APIC timer is active (PIT is switched off)
*/
if (num_possible_cpus() > 1 || is_hpet_enabled() ||
pit_clockevent.mode != CLOCK_EVT_MODE_PERIODIC)
return 0;
clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);