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Linux/arch/arm/lib/delay.c

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  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 }
 94 

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