LXR linux/arch/arm/kernel/arch

   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
  15#include <asm/delay.h>
  16#include <asm/sched_clock.h>
  17
  18#include <clocksource/arm_arch_timer.h>
  19
  20static unsigned long arch_timer_read_counter_long(void)
  21{
  22        return arch_timer_read_counter();
  23}
  24
  25static u32 sched_clock_mult __read_mostly;
  26
  27static unsigned long long notrace arch_timer_sched_clock(void)
  28{
  29        return arch_timer_read_counter() * sched_clock_mult;
  30}
  31
  32static struct delay_timer arch_delay_timer;
  33
  34static 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
  42int __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}
  59