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/export.h>
  28 #include <linux/timex.h>
  29
  30 /*
  31  * Default to the loop-based delay implementation.
  32  */
  33 struct arm_delay_ops arm_delay_ops __ro_after_init = {
  34         .delay          = __loop_delay,
  35         .const_udelay   = __loop_const_udelay,
  36         .udelay         = __loop_udelay,
  37 };
  38 EXPORT_SYMBOL(arm_delay_ops);
  39
  40 static const struct delay_timer *delay_timer;
  41 static bool delay_calibrated;
  42 static u64 delay_res;
  43
  44 int read_current_timer(unsigned long *timer_val)
  45 {
  46         if (!delay_timer)
  47                 return -ENXIO;
  48
  49         *timer_val = delay_timer->read_current_timer();
  50         return 0;
  51 }
  52 EXPORT_SYMBOL_GPL(read_current_timer);
  53
  54 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  55 {
  56         return (cyc * mult) >> shift;
  57 }
  58
  59 static void __timer_delay(unsigned long cycles)
  60 {
  61         cycles_t start = get_cycles();
  62
  63         while ((get_cycles() - start) < cycles)
  64                 cpu_relax();
  65 }
  66
  67 static void __timer_const_udelay(unsigned long xloops)
  68 {
  69         unsigned long long loops = xloops;
  70         loops *= arm_delay_ops.ticks_per_jiffy;
  71         __timer_delay(loops >> UDELAY_SHIFT);
  72 }
  73
  74 static void __timer_udelay(unsigned long usecs)
  75 {
  76         __timer_const_udelay(usecs * UDELAY_MULT);
  77 }
  78
  79 void __init register_current_timer_delay(const struct delay_timer *timer)
  80 {
  81         u32 new_mult, new_shift;
  82         u64 res;
  83
  84         clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
  85                                NSEC_PER_SEC, 3600);
  86         res = cyc_to_ns(1ULL, new_mult, new_shift);
  87
  88         if (res > 1000) {
  89                 pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
  90                         timer, res);
  91                 return;
  92         }
  93
  94         if (!delay_calibrated && (!delay_res || (res < delay_res))) {
  95                 pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
  96                 delay_timer                     = timer;
  97                 lpj_fine                        = timer->freq / HZ;
  98                 delay_res                       = res;
  99
 100                 /* cpufreq may scale loops_per_jiffy, so keep a private copy */
 101                 arm_delay_ops.ticks_per_jiffy   = lpj_fine;
 102                 arm_delay_ops.delay             = __timer_delay;
 103                 arm_delay_ops.const_udelay      = __timer_const_udelay;
 104                 arm_delay_ops.udelay            = __timer_udelay;
 105         } else {
 106                 pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
 107         }
 108 }
 109
 110 unsigned long calibrate_delay_is_known(void)
 111 {
 112         delay_calibrated = true;
 113         return lpj_fine;
 114 }
 115
 116 void calibration_delay_done(void)
 117 {
 118         delay_calibrated = true;
 119 }