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