[PATCH] x86_64: Calibrate APIC timer using PM timer

On some broken motherboards (at least one NForce3 based AMD64 laptop)
the PIT timer runs at a incorrect frequency.  This patch adds a new
option "apicpmtimer" that allows to use the APIC timer and calibrate it
using the PMTimer.  It requires the earlier patch that allows to run the
main timer from the APIC.

Specifying apicpmtimer implies apicmaintimer.

The option defaults to off for now.

I tested it on a few systems and the resulting APIC timer frequencies
were usually a bit off, but always <1%, which should be tolerable.

TBD figure out heuristic to enable this automatically on the affected
systems TBD perhaps do it on all NForce3s or using DMI?

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 27 insertions, 6 deletions

diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
index 673a2fe9923..c02218b3ae2 100644
--- a/arch/x86_64/kernel/apic.c
+++ b/arch/x86_64/kernel/apic.c
@@ -40,6 +40,7 @@
 
 int apic_verbosity;
 int apic_runs_main_timer;
+int apic_calibrate_pmtmr __initdata;
 
 int disable_apic_timer __initdata;
 
@@ -746,14 +747,27 @@ static int __init calibrate_APIC_clock(void)
         __setup_APIC_LVTT(1000000000);
 
         apic_start = apic_read(APIC_TMCCT);
-        rdtscl(tsc_start);
-
-        do {
+#ifdef CONFIG_X86_PM_TIMER
+        if (apic_calibrate_pmtmr && pmtmr_ioport) {
+                pmtimer_wait(5000);  /* 5ms wait */
                 apic = apic_read(APIC_TMCCT);
-                rdtscl(tsc);
-        } while ((tsc - tsc_start) < TICK_COUNT && (apic - apic_start) < TICK_COUNT);
+                result = (apic_start - apic) * 1000L / 5;
+        } else
+#endif
+        {
+                rdtscl(tsc_start);
+
+                do {
+                        apic = apic_read(APIC_TMCCT);
+                        rdtscl(tsc);
+                } while ((tsc - tsc_start) < TICK_COUNT &&
+                                (apic - apic_start) < TICK_COUNT);
+
+                result = (apic_start - apic) * 1000L * cpu_khz /
+                                        (tsc - tsc_start);
+        }
+        printk("result %d\n", result);
 
-        result = (apic_start - apic) * 1000L * cpu_khz / (tsc - tsc_start);
 
         printk(KERN_INFO "Detected %d.%03d MHz APIC timer.\n",
                 result / 1000 / 1000, result / 1000 % 1000);
@@ -1115,6 +1129,13 @@ static __init int setup_noapicmaintimer(char *str)
 }
 __setup("noapicmaintimer", setup_noapicmaintimer);
 
+static __init int setup_apicpmtimer(char *s)
+{
+        apic_calibrate_pmtmr = 1;
+        return setup_apicmaintimer(NULL);
+}
+__setup("apicpmtimer", setup_apicpmtimer);
+
 /* dummy parsing: see setup.c */
 
 __setup("disableapic", setup_disableapic);