Commit | Line | Data |
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35728b82 | 1 | // SPDX-License-Identifier: GPL-2.0+ |
6c7811c6 TG |
2 | /* |
3 | * This file contains the jiffies based clocksource. | |
4 | * | |
5 | * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) | |
6 | */ | |
734efb46 | 7 | #include <linux/clocksource.h> |
8 | #include <linux/jiffies.h> | |
fbad1ea9 | 9 | #include <linux/module.h> |
734efb46 | 10 | #include <linux/init.h> |
11 | ||
bfb83b27 | 12 | #include "timekeeping.h" |
e2830b5c | 13 | |
734efb46 | 14 | |
93825f2e | 15 | /* Since jiffies uses a simple TICK_NSEC multiplier |
734efb46 | 16 | * conversion, the .shift value could be zero. However |
17 | * this would make NTP adjustments impossible as they are | |
18 | * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to | |
19 | * shift both the nominator and denominator the same | |
20 | * amount, and give ntp adjustments in units of 1/2^8 | |
21 | * | |
22 | * The value 8 is somewhat carefully chosen, as anything | |
93825f2e FW |
23 | * larger can result in overflows. TICK_NSEC grows as HZ |
24 | * shrinks, so values greater than 8 overflow 32bits when | |
734efb46 | 25 | * HZ=100. |
26 | */ | |
80d767d7 MP |
27 | #if HZ < 34 |
28 | #define JIFFIES_SHIFT 6 | |
29 | #elif HZ < 67 | |
30 | #define JIFFIES_SHIFT 7 | |
31 | #else | |
734efb46 | 32 | #define JIFFIES_SHIFT 8 |
80d767d7 | 33 | #endif |
734efb46 | 34 | |
a5a1d1c2 | 35 | static u64 jiffies_read(struct clocksource *cs) |
734efb46 | 36 | { |
a5a1d1c2 | 37 | return (u64) jiffies; |
734efb46 | 38 | } |
39 | ||
93825f2e FW |
40 | /* |
41 | * The Jiffies based clocksource is the lowest common | |
42 | * denominator clock source which should function on | |
43 | * all systems. It has the same coarse resolution as | |
44 | * the timer interrupt frequency HZ and it suffers | |
45 | * inaccuracies caused by missed or lost timer | |
46 | * interrupts and the inability for the timer | |
47 | * interrupt hardware to accuratly tick at the | |
48 | * requested HZ value. It is also not recommended | |
49 | * for "tick-less" systems. | |
50 | */ | |
f95a9857 | 51 | static struct clocksource clocksource_jiffies = { |
734efb46 | 52 | .name = "jiffies", |
3f4a0b91 | 53 | .rating = 1, /* lowest valid rating*/ |
734efb46 | 54 | .read = jiffies_read, |
232d2637 | 55 | .mask = CLOCKSOURCE_MASK(32), |
93825f2e | 56 | .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */ |
734efb46 | 57 | .shift = JIFFIES_SHIFT, |
3c17ad19 | 58 | .max_cycles = 10, |
734efb46 | 59 | }; |
60 | ||
d6ad4187 JS |
61 | __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); |
62 | ||
fbad1ea9 TH |
63 | #if (BITS_PER_LONG < 64) |
64 | u64 get_jiffies_64(void) | |
65 | { | |
e1e41b6c | 66 | unsigned int seq; |
fbad1ea9 TH |
67 | u64 ret; |
68 | ||
69 | do { | |
d6ad4187 | 70 | seq = read_seqbegin(&jiffies_lock); |
fbad1ea9 | 71 | ret = jiffies_64; |
d6ad4187 | 72 | } while (read_seqretry(&jiffies_lock, seq)); |
fbad1ea9 TH |
73 | return ret; |
74 | } | |
75 | EXPORT_SYMBOL(get_jiffies_64); | |
76 | #endif | |
77 | ||
78 | EXPORT_SYMBOL(jiffies); | |
79 | ||
734efb46 | 80 | static int __init init_jiffies_clocksource(void) |
81 | { | |
f8935983 | 82 | return __clocksource_register(&clocksource_jiffies); |
734efb46 | 83 | } |
84 | ||
98de9e3b | 85 | core_initcall(init_jiffies_clocksource); |
f1b82746 MS |
86 | |
87 | struct clocksource * __init __weak clocksource_default_clock(void) | |
88 | { | |
89 | return &clocksource_jiffies; | |
90 | } | |
b3c869d3 | 91 | |
e8750053 | 92 | static struct clocksource refined_jiffies; |
b3c869d3 JS |
93 | |
94 | int register_refined_jiffies(long cycles_per_second) | |
95 | { | |
96 | u64 nsec_per_tick, shift_hz; | |
97 | long cycles_per_tick; | |
98 | ||
99 | ||
100 | ||
101 | refined_jiffies = clocksource_jiffies; | |
102 | refined_jiffies.name = "refined-jiffies"; | |
103 | refined_jiffies.rating++; | |
104 | ||
105 | /* Calc cycles per tick */ | |
106 | cycles_per_tick = (cycles_per_second + HZ/2)/HZ; | |
107 | /* shift_hz stores hz<<8 for extra accuracy */ | |
108 | shift_hz = (u64)cycles_per_second << 8; | |
109 | shift_hz += cycles_per_tick/2; | |
110 | do_div(shift_hz, cycles_per_tick); | |
111 | /* Calculate nsec_per_tick using shift_hz */ | |
fa3aa7a5 | 112 | nsec_per_tick = (u64)NSEC_PER_SEC << 8; |
b3c869d3 JS |
113 | nsec_per_tick += (u32)shift_hz/2; |
114 | do_div(nsec_per_tick, (u32)shift_hz); | |
115 | ||
116 | refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT; | |
117 | ||
f8935983 | 118 | __clocksource_register(&refined_jiffies); |
b3c869d3 JS |
119 | return 0; |
120 | } |