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

#define ACPI_PM_MASK 0xFFFFFF /* limit it to 24 bits */

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);

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