LXR linux/arch/arm/lib/delay.c

   1/*
   2 * Delay loops based on the OpenRISC implementation.
   3 *
   4 * Copyright (C) 2012 ARM Limited
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License version 2 as
   8 * published by the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful,
  11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 * GNU General Public License for more details.
  14 *
  15 * You should have received a copy of the GNU General Public License
  16 * along with this program; if not, write to the Free Software
  17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  18 *
  19 * Author: Will Deacon <will.deacon@arm.com>
  20 */
  21
  22#include <linux/delay.h>
  23#include <linux/init.h>
  24#include <linux/kernel.h>
  25#include <linux/module.h>
  26#include <linux/timex.h>
  27
  28/*
  29 * Default to the loop-based delay implementation.
  30 */
  31struct arm_delay_ops arm_delay_ops = {
  32        .delay          = __loop_delay,
  33        .const_udelay   = __loop_const_udelay,
  34        .udelay         = __loop_udelay,
  35};
  36
  37static const struct delay_timer *delay_timer;
  38static bool delay_calibrated;
  39
  40int read_current_timer(unsigned long *timer_val)
  41{
  42        if (!delay_timer)
  43                return -ENXIO;
  44
  45        *timer_val = delay_timer->read_current_timer();
  46        return 0;
  47}
  48EXPORT_SYMBOL_GPL(read_current_timer);
  49
  50static void __timer_delay(unsigned long cycles)
  51{
  52        cycles_t start = get_cycles();
  53
  54        while ((get_cycles() - start) < cycles)
  55                cpu_relax();
  56}
  57
  58static void __timer_const_udelay(unsigned long xloops)
  59{
  60        unsigned long long loops = xloops;
  61        loops *= arm_delay_ops.ticks_per_jiffy;
  62        __timer_delay(loops >> UDELAY_SHIFT);
  63}
  64
  65static void __timer_udelay(unsigned long usecs)
  66{
  67        __timer_const_udelay(usecs * UDELAY_MULT);
  68}
  69
  70void __init register_current_timer_delay(const struct delay_timer *timer)
  71{
  72        if (!delay_calibrated) {
  73                pr_info("Switching to timer-based delay loop\n");
  74                delay_timer                     = timer;
  75                lpj_fine                        = timer->freq / HZ;
  76
  77                /* cpufreq may scale loops_per_jiffy, so keep a private copy */
  78                arm_delay_ops.ticks_per_jiffy   = lpj_fine;
  79                arm_delay_ops.delay             = __timer_delay;
  80                arm_delay_ops.const_udelay      = __timer_const_udelay;
  81                arm_delay_ops.udelay            = __timer_udelay;
  82
  83                delay_calibrated                = true;
  84        } else {
  85                pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
  86        }
  87}
  88
  89unsigned long __cpuinit calibrate_delay_is_known(void)
  90{
  91        delay_calibrated = true;
  92        return lpj_fine;
  93}
  94