arch/arm/kernel/arch_timer.c

   1 /*
   2  *  linux/arch/arm/kernel/arch_timer.c
   3  *
   4  *  Copyright (C) 2011 ARM Ltd.
   5  *  All Rights Reserved
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11 #include <linux/init.h>
  12 #include <linux/types.h>
  13 #include <linux/errno.h>
  14 #include <linux/sched_clock.h>
  15
  16 #include <asm/delay.h>
  17
  18 #include <clocksource/arm_arch_timer.h>
  19
  20 static unsigned long arch_timer_read_counter_long(void)
  21 {
  22         return arch_timer_read_counter();
  23 }
  24
  25 static u32 sched_clock_mult __read_mostly;
  26
  27 static unsigned long long notrace arch_timer_sched_clock(void)
  28 {
  29         return arch_timer_read_counter() * sched_clock_mult;
  30 }
  31
  32 static struct delay_timer arch_delay_timer;
  33
  34 static void __init arch_timer_delay_timer_register(void)
  35 {
  36         /* Use the architected timer for the delay loop. */
  37         arch_delay_timer.read_current_timer = arch_timer_read_counter_long;
  38         arch_delay_timer.freq = arch_timer_get_rate();
  39         register_current_timer_delay(&arch_delay_timer);
  40 }
  41
  42 int __init arch_timer_arch_init(void)
  43 {
  44         u32 arch_timer_rate = arch_timer_get_rate();
  45
  46         if (arch_timer_rate == 0)
  47                 return -ENXIO;
  48
  49         arch_timer_delay_timer_register();
  50
  51         /* Cache the sched_clock multiplier to save a divide in the hot path. */
  52         sched_clock_mult = NSEC_PER_SEC / arch_timer_rate;
  53         sched_clock_func = arch_timer_sched_clock;
  54         pr_info("sched_clock: ARM arch timer >56 bits at %ukHz, resolution %uns\n",
  55                 arch_timer_rate / 1000, sched_clock_mult);
  56
  57         return 0;
  58 }