linux/arch/x86/kernel/pmtimer_64.c

/* Ported over from i386 by AK, original copyright was:
 *
 * (C) Dominik Brodowski <linux@brodo.de> 2003
 *
 * Driver to use the Power Management Timer (PMTMR) available in some
 * southbridges as primary timing source for the Linux kernel.
 *
 * Based on parts of linux/drivers/acpi/hardware/hwtimer.c, timer_pit.c,
 * timer_hpet.c, and on Arjan van de Ven's implementation for 2.4.
 *
 * This file is licensed under the GPL v2.
 *
 * Dropped all the hardware bug workarounds for now. Hopefully they
 * are not needed on 64bit chipsets.
 */

#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/cpumask.h>
#include <linux/acpi_pmtmr.h>

#include <asm/io.h>
#include <asm/proto.h>
#include <asm/msr.h>
#include <asm/vsyscall.h>

static inline u32 cyc2us(u32 cycles)
{
	/* The Power Management Timer ticks at 3.579545 ticks per microsecond.
	 * 1 / PM_TIMER_FREQUENCY == 0.27936511 =~ 286/1024 [error: 0.024%]
	 *
	 * Even with HZ = 100, delta is at maximum 35796 ticks, so it can
	 * easily be multiplied with 286 (=0x11E) without having to fear
	 * u32 overflows.
	 */
	cycles *= 286;
	return (cycles >> 10);
}

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

static int __init nopmtimer_setup(char *s)
{
	pmtmr_ioport = 0;
	return 1;
}

__setup("nopmtimer", nopmtimer_setup);