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

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/arch/ia64/sn/kernel/sn2/timer.c
   4  *
   5  * Copyright (C) 2003 Silicon Graphics, Inc.
   6  * Copyright (C) 2003 Hewlett-Packard Co
   7  *      David Mosberger <davidm@hpl.hp.com>: updated for new timer-interpolation infrastructure
   8  */
   9
  10 #include <linux/init.h>
  11 #include <linux/kernel.h>
  12 #include <linux/sched.h>
  13 #include <linux/time.h>
  14 #include <linux/interrupt.h>
  15 #include <linux/clocksource.h>
  16
  17 #include <asm/hw_irq.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 u64 read_sn2(struct clocksource *cs)
  27 {
  28         return (u64)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         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  37 };
  38
  39 /*
  40  * sn udelay uses the RTC instead of the ITC because the ITC is not
  41  * synchronized across all CPUs, and the thread may migrate to another CPU
  42  * if preemption is enabled.
  43  */
  44 static void
  45 ia64_sn_udelay (unsigned long usecs)
  46 {
  47         unsigned long start = rtc_time();
  48         unsigned long end = start +
  49                         usecs * sn_rtc_cycles_per_second / 1000000;
  50
  51         while (time_before((unsigned long)rtc_time(), end))
  52                 cpu_relax();
  53 }
  54
  55 void __init sn_timer_init(void)
  56 {
  57         clocksource_sn2.archdata.fsys_mmio = RTC_COUNTER_ADDR;
  58         clocksource_register_hz(&clocksource_sn2, sn_rtc_cycles_per_second);
  59
  60         ia64_udelay = &ia64_sn_udelay;
  61 }