1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Delay loops based on the OpenRISC implementation. 4 * 5 * Copyright (C) 2012 ARM Limited 6 * 7 * Author: Will Deacon <will.deacon@arm.com> 8 */ 9 10 #include <linux/clocksource.h> 11 #include <linux/delay.h> 12 #include <linux/init.h> 13 #include <linux/kernel.h> 14 #include <linux/module.h> 15 #include <linux/timex.h> 16 17 /* 18 * Default to the loop-based delay implementation. 19 */ 20 struct arm_delay_ops arm_delay_ops __ro_after_init = { 21 .delay = __loop_delay, 22 .const_udelay = __loop_const_udelay, 23 .udelay = __loop_udelay, 24 }; 25 26 static const struct delay_timer *delay_timer; 27 static bool delay_calibrated; 28 static u64 delay_res; 29 30 int read_current_timer(unsigned long *timer_val) 31 { 32 if (!delay_timer) 33 return -ENXIO; 34 35 *timer_val = delay_timer->read_current_timer(); 36 return 0; 37 } 38 EXPORT_SYMBOL_GPL(read_current_timer); 39 40 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift) 41 { 42 return (cyc * mult) >> shift; 43 } 44 45 static void __timer_delay(unsigned long cycles) 46 { 47 cycles_t start = get_cycles(); 48 49 while ((get_cycles() - start) < cycles) 50 cpu_relax(); 51 } 52 53 static void __timer_const_udelay(unsigned long xloops) 54 { 55 unsigned long long loops = xloops; 56 loops *= arm_delay_ops.ticks_per_jiffy; 57 __timer_delay(loops >> UDELAY_SHIFT); 58 } 59 60 static void __timer_udelay(unsigned long usecs) 61 { 62 __timer_const_udelay(usecs * UDELAY_MULT); 63 } 64 65 void __init register_current_timer_delay(const struct delay_timer *timer) 66 { 67 u32 new_mult, new_shift; 68 u64 res; 69 70 clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq, 71 NSEC_PER_SEC, 3600); 72 res = cyc_to_ns(1ULL, new_mult, new_shift); 73 74 if (res > 1000) { 75 pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n", 76 timer, res); 77 return; 78 } 79 80 if (!delay_calibrated && (!delay_res || (res < delay_res))) { 81 pr_info("Switching to timer-based delay loop, resolution %lluns\n", res); 82 delay_timer = timer; 83 lpj_fine = timer->freq / HZ; 84 delay_res = res; 85 86 /* cpufreq may scale loops_per_jiffy, so keep a private copy */ 87 arm_delay_ops.ticks_per_jiffy = lpj_fine; 88 arm_delay_ops.delay = __timer_delay; 89 arm_delay_ops.const_udelay = __timer_const_udelay; 90 arm_delay_ops.udelay = __timer_udelay; 91 } else { 92 pr_info("Ignoring duplicate/late registration of read_current_timer delay\n"); 93 } 94 } 95 96 unsigned long calibrate_delay_is_known(void) 97 { 98 delay_calibrated = true; 99 return lpj_fine; 100 } 101 102 void calibration_delay_done(void) 103 { 104 delay_calibrated = true; 105 } 106