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" |
d25a0252 | 13 | #include "tick-internal.h" |
e2830b5c | 14 | |
734efb46 | 15 | |
a5a1d1c2 | 16 | static u64 jiffies_read(struct clocksource *cs) |
734efb46 | 17 | { |
a5a1d1c2 | 18 | return (u64) jiffies; |
734efb46 | 19 | } |
20 | ||
93825f2e FW |
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 | |
4bf07f65 | 28 | * interrupt hardware to accurately tick at the |
93825f2e FW |
29 | * requested HZ value. It is also not recommended |
30 | * for "tick-less" systems. | |
31 | */ | |
f95a9857 | 32 | static struct clocksource clocksource_jiffies = { |
2e27e793 PM |
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, | |
734efb46 | 41 | }; |
42 | ||
e5d4d175 | 43 | __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock); |
1a2b85f1 DB |
44 | __cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq = |
45 | SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock); | |
d6ad4187 | 46 | |
fbad1ea9 TH |
47 | #if (BITS_PER_LONG < 64) |
48 | u64 get_jiffies_64(void) | |
49 | { | |
e1e41b6c | 50 | unsigned int seq; |
fbad1ea9 TH |
51 | u64 ret; |
52 | ||
53 | do { | |
e5d4d175 | 54 | seq = read_seqcount_begin(&jiffies_seq); |
fbad1ea9 | 55 | ret = jiffies_64; |
e5d4d175 | 56 | } while (read_seqcount_retry(&jiffies_seq, seq)); |
fbad1ea9 TH |
57 | return ret; |
58 | } | |
59 | EXPORT_SYMBOL(get_jiffies_64); | |
60 | #endif | |
61 | ||
62 | EXPORT_SYMBOL(jiffies); | |
63 | ||
734efb46 | 64 | static int __init init_jiffies_clocksource(void) |
65 | { | |
f8935983 | 66 | return __clocksource_register(&clocksource_jiffies); |
734efb46 | 67 | } |
68 | ||
98de9e3b | 69 | core_initcall(init_jiffies_clocksource); |
f1b82746 MS |
70 | |
71 | struct clocksource * __init __weak clocksource_default_clock(void) | |
72 | { | |
73 | return &clocksource_jiffies; | |
74 | } | |
b3c869d3 | 75 | |
e8750053 | 76 | static struct clocksource refined_jiffies; |
b3c869d3 JS |
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 */ | |
fa3aa7a5 | 96 | nsec_per_tick = (u64)NSEC_PER_SEC << 8; |
b3c869d3 JS |
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 | ||
f8935983 | 102 | __clocksource_register(&refined_jiffies); |
b3c869d3 JS |
103 | return 0; |
104 | } |