Commit 0c3749c4 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[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: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 099f318b

Documentation/x86_64/boot-options.txt

+5 −0
Original line number Diff line number Diff line
@@ -47,6 +47,11 @@ APICs 
   noapicmaintimer  Don't do time keeping using the APIC timer.

		 Useful when this option was auto selected, but doesn't work.



   apicpmtimer

		 Do APIC timer calibration using the pmtimer. Implies

		 apicmaintimer. Useful when your PIT timer is totally

		 broken.



Early Console



   syntax: earlyprintk=vga

arch/x86_64/kernel/apic.c

+27 −6
Original line number Diff line number Diff line
@@ -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);

#ifdef CONFIG_X86_PM_TIMER

	if (apic_calibrate_pmtmr && pmtmr_ioport) {

		pmtimer_wait(5000);  /* 5ms wait */

		apic = apic_read(APIC_TMCCT);

		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);

		} 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);

arch/x86_64/kernel/pmtimer.c

+20 −0
Original line number Diff line number Diff line
@@ -80,6 +80,26 @@ int pmtimer_mark_offset(void) 
	return lost - 1;

}



static unsigned pmtimer_wait_tick(void)

{

	u32 a, b;

	for (a = b = inl(pmtmr_ioport) & ACPI_PM_MASK;

	     a == b;

	     b = inl(pmtmr_ioport) & ACPI_PM_MASK)

		;

	return b;

}



/* note: wait time is rounded up to one tick */

void pmtimer_wait(unsigned us)

{

	u32 a, b;

	a = pmtimer_wait_tick();

	do {

		b = inl(pmtmr_ioport);

	} while (cyc2us(b - a) < us);

}



void pmtimer_resume(void)

{

	last_pmtmr_tick = inl(pmtmr_ioport);

include/asm-x86_64/proto.h

+1 −0
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ extern void iommu_hole_init(void); 
extern void time_init_gtod(void);

extern int pmtimer_mark_offset(void);

extern void pmtimer_resume(void);

extern void pmtimer_wait(unsigned);

extern unsigned int do_gettimeoffset_pm(void);

#ifdef CONFIG_X86_PM_TIMER

extern u32 pmtmr_ioport;

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