arch/x86_64/kernel/pmtimer.c

   1 /* Ported over from i386 by AK, original copyright was:
   2  *
   3  * (C) Dominik Brodowski <linux@brodo.de> 2003
   4  *
   5  * Driver to use the Power Management Timer (PMTMR) available in some
   6  * southbridges as primary timing source for the Linux kernel.
   7  *
   8  * Based on parts of linux/drivers/acpi/hardware/hwtimer.c, timer_pit.c,
   9  * timer_hpet.c, and on Arjan van de Ven's implementation for 2.4.
  10  *
  11  * This file is licensed under the GPL v2.
  12  *
  13  * Dropped all the hardware bug workarounds for now. Hopefully they
  14  * are not needed on 64bit chipsets.
  15  */
  16
  17 #include <linux/jiffies.h>
  18 #include <linux/kernel.h>
  19 #include <linux/time.h>
  20 #include <linux/init.h>
  21 #include <linux/cpumask.h>
  22 #include <asm/io.h>
  23 #include <asm/proto.h>
  24 #include <asm/msr.h>
  25 #include <asm/vsyscall.h>
  26
  27 #define ACPI_PM_MASK 0xFFFFFF /* limit it to 24 bits */
  28
  29 static inline u32 cyc2us(u32 cycles)
  30 {
  31         /* The Power Management Timer ticks at 3.579545 ticks per microsecond.
  32          * 1 / PM_TIMER_FREQUENCY == 0.27936511 =~ 286/1024 [error: 0.024%]
  33          *
  34          * Even with HZ = 100, delta is at maximum 35796 ticks, so it can
  35          * easily be multiplied with 286 (=0x11E) without having to fear
  36          * u32 overflows.
  37          */
  38         cycles *= 286;
  39         return (cycles >> 10);
  40 }
  41
  42 static unsigned pmtimer_wait_tick(void)
  43 {
  44         u32 a, b;
  45         for (a = b = inl(pmtmr_ioport) & ACPI_PM_MASK;
  46              a == b;
  47              b = inl(pmtmr_ioport) & ACPI_PM_MASK)
  48                 cpu_relax();
  49         return b;
  50 }
  51
  52 /* note: wait time is rounded up to one tick */
  53 void pmtimer_wait(unsigned us)
  54 {
  55         u32 a, b;
  56         a = pmtimer_wait_tick();
  57         do {
  58                 b = inl(pmtmr_ioport);
  59                 cpu_relax();
  60         } while (cyc2us(b - a) < us);
  61 }
  62
  63 static int __init nopmtimer_setup(char *s)
  64 {
  65         pmtmr_ioport = 0;
  66         return 1;
  67 }
  68
  69 __setup("nopmtimer", nopmtimer_setup);