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   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 #include <linux/clocksource.h>
  15
  16 #include <asm/hw_irq.h>
  17 #include <asm/system.h>
  18 #include <asm/timex.h>
  19
  20 #include <asm/sn/leds.h>
  21 #include <asm/sn/shub_mmr.h>
  22 #include <asm/sn/clksupport.h>
  23
  24 extern unsigned long sn_rtc_cycles_per_second;
  25
  26 static cycle_t read_sn2(void)
  27 {
  28         return (cycle_t)readq(RTC_COUNTER_ADDR);
  29 }
  30
  31 static struct clocksource clocksource_sn2 = {
  32         .name           = "sn2_rtc",
  33         .rating         = 450,
  34         .read           = read_sn2,
  35         .mask           = (1LL << 55) - 1,
  36         .mult           = 0,
  37         .shift          = 10,
  38         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  39 };
  40
  41 /*
  42  * sn udelay uses the RTC instead of the ITC because the ITC is not
  43  * synchronized across all CPUs, and the thread may migrate to another CPU
  44  * if preemption is enabled.
  45  */
  46 static void
  47 ia64_sn_udelay (unsigned long usecs)
  48 {
  49         unsigned long start = rtc_time();
  50         unsigned long end = start +
  51                         usecs * sn_rtc_cycles_per_second / 1000000;
  52
  53         while (time_before((unsigned long)rtc_time(), end))
  54                 cpu_relax();
  55 }
  56
  57 void __init sn_timer_init(void)
  58 {
  59         clocksource_sn2.fsys_mmio = RTC_COUNTER_ADDR;
  60         clocksource_sn2.mult = clocksource_hz2mult(sn_rtc_cycles_per_second,
  61                                                         clocksource_sn2.shift);
  62         clocksource_register(&clocksource_sn2);
  63
  64         ia64_udelay = &ia64_sn_udelay;
  65 }