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 __cpuinit calibrate_delay_is_known(void) 90 { 91 delay_calibrated = true; 92 return lpj_fine; 93 } 94