x86 ACPI: Add support for Always Running APIC timer

Add support for Always Running APIC timer, CPUID_0x6_EAX_Bit2.
This bit means the APIC timer continues to run even when CPU is
in deep C-states.

The advantage is that we can use LAPIC timer on these CPUs
always, and there is no need for "slow to read and program"
external timers (HPET/PIT) and the timer broadcast logic
and related code in C-state entry and exit.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 098ec84b8c00..f2870920f246 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -431,6 +431,12 @@ static void __cpuinit setup_APIC_timer(void)
 {
         struct clock_event_device *levt = &__get_cpu_var(lapic_events);
 
+        if (cpu_has(&current_cpu_data, X86_FEATURE_ARAT)) {
+                lapic_clockevent.features &= ~CLOCK_EVT_FEAT_C3STOP;
+                /* Make LAPIC timer preferrable over percpu HPET */
+                lapic_clockevent.rating = 150;
+        }
+
         memcpy(levt, &lapic_clockevent, sizeof(*levt));
         levt->cpumask = cpumask_of(smp_processor_id());