1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * This file contains the jiffies based clocksource. 4 * 5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) 6 */ 7 #include <linux/clocksource.h> 8 #include <linux/jiffies.h> 9 #include <linux/module.h> 10 #include <linux/init.h> 11 12 #include "timekeeping.h" 13 #include "tick-internal.h" 14 15 16 static u64 jiffies_read(struct clocksource *cs) 17 { 18 return (u64) jiffies; 19 } 20 21 /* 22 * The Jiffies based clocksource is the lowest common 23 * denominator clock source which should function on 24 * all systems. It has the same coarse resolution as 25 * the timer interrupt frequency HZ and it suffers 26 * inaccuracies caused by missed or lost timer 27 * interrupts and the inability for the timer 28 * interrupt hardware to accurately tick at the 29 * requested HZ value. It is also not recommended 30 * for "tick-less" systems. 31 */ 32 static struct clocksource clocksource_jiffies = { 33 .name = "jiffies", 34 .rating = 1, /* lowest valid rating*/ 35 .uncertainty_margin = 32 * NSEC_PER_MSEC, 36 .read = jiffies_read, 37 .mask = CLOCKSOURCE_MASK(32), 38 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */ 39 .shift = JIFFIES_SHIFT, 40 .max_cycles = 10, 41 }; 42 43 __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock); 44 __cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq = 45 SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock); 46 47 #if (BITS_PER_LONG < 64) 48 u64 get_jiffies_64(void) 49 { 50 unsigned int seq; 51 u64 ret; 52 53 do { 54 seq = read_seqcount_begin(&jiffies_seq); 55 ret = jiffies_64; 56 } while (read_seqcount_retry(&jiffies_seq, seq)); 57 return ret; 58 } 59 EXPORT_SYMBOL(get_jiffies_64); 60 #endif 61 62 EXPORT_SYMBOL(jiffies); 63 64 static int __init init_jiffies_clocksource(void) 65 { 66 return __clocksource_register(&clocksource_jiffies); 67 } 68 69 core_initcall(init_jiffies_clocksource); 70 71 struct clocksource * __init __weak clocksource_default_clock(void) 72 { 73 return &clocksource_jiffies; 74 } 75 76 static struct clocksource refined_jiffies; 77 78 int register_refined_jiffies(long cycles_per_second) 79 { 80 u64 nsec_per_tick, shift_hz; 81 long cycles_per_tick; 82 83 84 85 refined_jiffies = clocksource_jiffies; 86 refined_jiffies.name = "refined-jiffies"; 87 refined_jiffies.rating++; 88 89 /* Calc cycles per tick */ 90 cycles_per_tick = (cycles_per_second + HZ/2)/HZ; 91 /* shift_hz stores hz<<8 for extra accuracy */ 92 shift_hz = (u64)cycles_per_second << 8; 93 shift_hz += cycles_per_tick/2; 94 do_div(shift_hz, cycles_per_tick); 95 /* Calculate nsec_per_tick using shift_hz */ 96 nsec_per_tick = (u64)NSEC_PER_SEC << 8; 97 nsec_per_tick += (u32)shift_hz/2; 98 do_div(nsec_per_tick, (u32)shift_hz); 99 100 refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT; 101 102 __clocksource_register(&refined_jiffies); 103 return 0; 104 } 105