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  */
  31 struct arm_delay_ops arm_delay_ops = {
  32         .delay          = __loop_delay,
  33         .const_udelay   = __loop_const_udelay,
  34         .udelay         = __loop_udelay,
  35 };
  36
  37 static const struct delay_timer *delay_timer;
  38 static bool delay_calibrated;
  39
  40 int 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 }
  48 EXPORT_SYMBOL_GPL(read_current_timer);
  49
  50 static 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
  58 static 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
  65 static void __timer_udelay(unsigned long usecs)
  66 {
  67         __timer_const_udelay(usecs * UDELAY_MULT);
  68 }
  69
  70 void __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
  89 unsigned long calibrate_delay_is_known(void)
  90 {
  91         delay_calibrated = true;
  92         return lpj_fine;
  93 }