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/clocksource.h>
  23#include <linux/delay.h>
  24#include <linux/init.h>
  25#include <linux/kernel.h>
  26#include <linux/module.h>
  27#include <linux/timex.h>
  28
  29/*
  30 * Default to the loop-based delay implementation.
  31 */
  32struct arm_delay_ops arm_delay_ops = {
  33        .delay          = __loop_delay,
  34        .const_udelay   = __loop_const_udelay,
  35        .udelay         = __loop_udelay,
  36};
  37
  38static const struct delay_timer *delay_timer;
  39static bool delay_calibrated;
  40static u64 delay_res;
  41
  42int read_current_timer(unsigned long *timer_val)
  43{
  44        if (!delay_timer)
  45                return -ENXIO;
  46
  47        *timer_val = delay_timer->read_current_timer();
  48        return 0;
  49}
  50EXPORT_SYMBOL_GPL(read_current_timer);
  51
  52static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  53{
  54        return (cyc * mult) >> shift;
  55}
  56
  57static void __timer_delay(unsigned long cycles)
  58{
  59        cycles_t start = get_cycles();
  60
  61        while ((get_cycles() - start) < cycles)
  62                cpu_relax();
  63}
  64
  65static void __timer_const_udelay(unsigned long xloops)
  66{
  67        unsigned long long loops = xloops;
  68        loops *= arm_delay_ops.ticks_per_jiffy;
  69        __timer_delay(loops >> UDELAY_SHIFT);
  70}
  71
  72static void __timer_udelay(unsigned long usecs)
  73{
  74        __timer_const_udelay(usecs * UDELAY_MULT);
  75}
  76
  77void __init register_current_timer_delay(const struct delay_timer *timer)
  78{
  79        u32 new_mult, new_shift;
  80        u64 res;
  81
  82        clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
  83                               NSEC_PER_SEC, 3600);
  84        res = cyc_to_ns(1ULL, new_mult, new_shift);
  85
  86        if (res > 1000) {
  87                pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
  88                        timer, res);
  89                return;
  90        }
  91
  92        if (!delay_calibrated && (!delay_res || (res < delay_res))) {
  93                pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
  94                delay_timer                     = timer;
  95                lpj_fine                        = timer->freq / HZ;
  96                delay_res                       = res;
  97
  98                /* cpufreq may scale loops_per_jiffy, so keep a private copy */
  99                arm_delay_ops.ticks_per_jiffy   = lpj_fine;
 100                arm_delay_ops.delay             = __timer_delay;
 101                arm_delay_ops.const_udelay      = __timer_const_udelay;
 102                arm_delay_ops.udelay            = __timer_udelay;
 103        } else {
 104                pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
 105        }
 106}
 107
 108unsigned long calibrate_delay_is_known(void)
 109{
 110        delay_calibrated = true;
 111        return lpj_fine;
 112}
 113
 114void calibration_delay_done(void)
 115{
 116        delay_calibrated = true;
 117}
 118