[PATCH 3/8] x86/apic: allow use of lapic timer early calibration result

Jacob Pan
2010-05-07T17:47:22Z

From: Jacob Pan <jacob.jun.pan@intel.com>

lapic timer calibration can be combined with tsc in platform specific
calibration functions. if such calibration result is obtained early,
we can skip the redundent calibration loops.

Signed-off-by: Jacob Pan <jacob.jun.pan@intel.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
arch/x86/kernel/apic/apic.c | 21 ++++++++++++++++++++-
1 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index e5a4a1e..8ef56ac 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -175,7 +175,7 @@ static struct resource lapic_resource = {
.flags = IORESOURCE_MEM | IORESOURCE_BUSY,
};

-static unsigned int calibration_result;
+unsigned int calibration_result;

static int lapic_next_event(unsigned long delta,
struct clock_event_device *evt);
@@ -597,6 +597,25 @@ static int __init calibrate_APIC_clock(void)
long delta, deltatsc;
int pm_referenced = 0;

+ /**
+ * check if lapic timer has already been calibrated by platform
+ * specific routine, such as tsc calibration code. if so, we just fill
+ * in the clockevent structure and return.
+ */
+
+ if (calibration_result) {
+ apic_printk(APIC_VERBOSE, "lapic timer already calibrated %d\n",
+ calibration_result);
+ lapic_clockevent.mult = div_sc(calibration_result/APIC_DIVISOR,
+ TICK_NSEC, lapic_clockevent.shift);
+ lapic_clockevent.max_delta_ns =
+ clockevent_delta2ns(0x7FFFFF, &lapic_clockevent);
+ lapic_clockevent.min_delta_ns =
+ clockevent_delta2ns(0xF, &lapic_clockevent);
+ lapic_clockevent.features &= ~CLOCK_EVT_FEAT_DUMMY;
+ return 0;
+ }
+
local_irq_disable();

/* Replace the global interrupt handler */
--
1.6.3.3