arch/i386/kernel/hpet.c

   1 #include <linux/clocksource.h>
   2 #include <linux/errno.h>
   3 #include <linux/hpet.h>
   4 #include <linux/init.h>
   5
   6 #include <asm/hpet.h>
   7 #include <asm/io.h>
   8
   9 #define HPET_MASK       CLOCKSOURCE_MASK(32)
  10 #define HPET_SHIFT      22
  11
  12 /* FSEC = 10^-15 NSEC = 10^-9 */
  13 #define FSEC_PER_NSEC   1000000
  14
  15 static void *hpet_ptr;
  16
  17 static cycle_t read_hpet(void)
  18 {
  19         return (cycle_t)readl(hpet_ptr);
  20 }
  21
  22 static struct clocksource clocksource_hpet = {
  23         .name           = "hpet",
  24         .rating         = 250,
  25         .read           = read_hpet,
  26         .mask           = HPET_MASK,
  27         .mult           = 0, /* set below */
  28         .shift          = HPET_SHIFT,
  29         .is_continuous  = 1,
  30 };
  31
  32 static int __init init_hpet_clocksource(void)
  33 {
  34         unsigned long hpet_period;
  35         void __iomem* hpet_base;
  36         u64 tmp;
  37         int err;
  38
  39         if (!is_hpet_enabled())
  40                 return -ENODEV;
  41
  42         /* calculate the hpet address: */
  43         hpet_base =
  44                 (void __iomem*)ioremap_nocache(hpet_address, HPET_MMAP_SIZE);
  45         hpet_ptr = hpet_base + HPET_COUNTER;
  46
  47         /* calculate the frequency: */
  48         hpet_period = readl(hpet_base + HPET_PERIOD);
  49
  50         /*
  51          * hpet period is in femto seconds per cycle
  52          * so we need to convert this to ns/cyc units
  53          * aproximated by mult/2^shift
  54          *
  55          *  fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift
  56          *  fsec/cyc * 1ns/1000000fsec * 2^shift = mult
  57          *  fsec/cyc * 2^shift * 1nsec/1000000fsec = mult
  58          *  (fsec/cyc << shift)/1000000 = mult
  59          *  (hpet_period << shift)/FSEC_PER_NSEC = mult
  60          */
  61         tmp = (u64)hpet_period << HPET_SHIFT;
  62         do_div(tmp, FSEC_PER_NSEC);
  63         clocksource_hpet.mult = (u32)tmp;
  64
  65         err = clocksource_register(&clocksource_hpet);
  66         if (err)
  67                 iounmap(hpet_base);
  68
  69         return err;
  70 }
  71
  72 module_init(init_hpet_clocksource);