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
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