arch/ia64/sn/kernel/sn2/timer.c

   1 /*
   2  * linux/arch/ia64/sn/kernel/sn2/timer.c
   3  *
   4  * Copyright (C) 2003 Silicon Graphics, Inc.
   5  * Copyright (C) 2003 Hewlett-Packard Co
   6  *      David Mosberger <davidm@hpl.hp.com>: updated for new timer-interpolation infrastructure
   7  */
   8
   9 #include <linux/init.h>
  10 #include <linux/kernel.h>
  11 #include <linux/sched.h>
  12 #include <linux/time.h>
  13 #include <linux/interrupt.h>
  14
  15 #include <asm/hw_irq.h>
  16 #include <asm/system.h>
  17
  18 #include <asm/sn/leds.h>
  19 #include <asm/sn/clksupport.h>
  20
  21
  22 extern unsigned long sn_rtc_cycles_per_second;
  23 static volatile unsigned long last_wall_rtc;
  24
  25 static unsigned long rtc_offset;        /* updated only when xtime write-lock is held! */
  26 static long rtc_nsecs_per_cycle;
  27 static long rtc_per_timer_tick;
  28
  29 static unsigned long
  30 getoffset(void)
  31 {
  32         return rtc_offset + (GET_RTC_COUNTER() - last_wall_rtc)*rtc_nsecs_per_cycle;
  33 }
  34
  35
  36 static void
  37 update(long delta_nsec)
  38 {
  39         unsigned long rtc_counter = GET_RTC_COUNTER();
  40         unsigned long offset = rtc_offset + (rtc_counter - last_wall_rtc)*rtc_nsecs_per_cycle;
  41
  42         /* Be careful about signed/unsigned comparisons here: */
  43         if (delta_nsec < 0 || (unsigned long) delta_nsec < offset)
  44                 rtc_offset = offset - delta_nsec;
  45         else
  46                 rtc_offset = 0;
  47         last_wall_rtc = rtc_counter;
  48 }
  49
  50
  51 static void
  52 reset(void)
  53 {
  54         rtc_offset = 0;
  55         last_wall_rtc = GET_RTC_COUNTER();
  56 }
  57
  58
  59 static struct time_interpolator sn2_interpolator = {
  60         .get_offset =   getoffset,
  61         .update =       update,
  62         .reset =        reset
  63 };
  64
  65 void __init
  66 sn_timer_init(void)
  67 {
  68         sn2_interpolator.frequency = sn_rtc_cycles_per_second;
  69         sn2_interpolator.drift = -1;    /* unknown */
  70         register_time_interpolator(&sn2_interpolator);
  71
  72         rtc_per_timer_tick = sn_rtc_cycles_per_second / HZ;
  73         rtc_nsecs_per_cycle = 1000000000 / sn_rtc_cycles_per_second;
  74
  75         last_wall_rtc = GET_RTC_COUNTER();
  76 }