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 } 120