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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
14
15/* Since jiffies uses a simple TICK_NSEC multiplier
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
23 * larger can result in overflows. TICK_NSEC grows as HZ
24 * shrinks, so values greater than 8 overflow 32bits when
25 * HZ=100.
26 */
27#if HZ < 34
28#define JIFFIES_SHIFT 6
29#elif HZ < 67
30#define JIFFIES_SHIFT 7
31#else
32#define JIFFIES_SHIFT 8
33#endif
34
35static u64 jiffies_read(struct clocksource *cs)
36{
37 return (u64) jiffies;
38}
39
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 accurately tick at the
48 * requested HZ value. It is also not recommended
49 * for "tick-less" systems.
50 */
51static struct clocksource clocksource_jiffies = {
52 .name = "jiffies",
53 .rating = 1, /* lowest valid rating*/
54 .uncertainty_margin = 32 * NSEC_PER_MSEC,
55 .read = jiffies_read,
56 .mask = CLOCKSOURCE_MASK(32),
57 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
58 .shift = JIFFIES_SHIFT,
59 .max_cycles = 10,
60};
61
62__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
63__cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq =
64 SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock);
65
66#if (BITS_PER_LONG < 64)
67u64 get_jiffies_64(void)
68{
69 unsigned int seq;
70 u64 ret;
71
72 do {
73 seq = read_seqcount_begin(&jiffies_seq);
74 ret = jiffies_64;
75 } while (read_seqcount_retry(&jiffies_seq, seq));
76 return ret;
77}
78EXPORT_SYMBOL(get_jiffies_64);
79#endif
80
81EXPORT_SYMBOL(jiffies);
82
83static int __init init_jiffies_clocksource(void)
84{
85 return __clocksource_register(&clocksource_jiffies);
86}
87
88core_initcall(init_jiffies_clocksource);
89
90struct clocksource * __init __weak clocksource_default_clock(void)
91{
92 return &clocksource_jiffies;
93}
94
95static struct clocksource refined_jiffies;
96
97int register_refined_jiffies(long cycles_per_second)
98{
99 u64 nsec_per_tick, shift_hz;
100 long cycles_per_tick;
101
102
103
104 refined_jiffies = clocksource_jiffies;
105 refined_jiffies.name = "refined-jiffies";
106 refined_jiffies.rating++;
107
108 /* Calc cycles per tick */
109 cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
110 /* shift_hz stores hz<<8 for extra accuracy */
111 shift_hz = (u64)cycles_per_second << 8;
112 shift_hz += cycles_per_tick/2;
113 do_div(shift_hz, cycles_per_tick);
114 /* Calculate nsec_per_tick using shift_hz */
115 nsec_per_tick = (u64)NSEC_PER_SEC << 8;
116 nsec_per_tick += (u32)shift_hz/2;
117 do_div(nsec_per_tick, (u32)shift_hz);
118
119 refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
120
121 __clocksource_register(&refined_jiffies);
122 return 0;
123}
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
14
15/* Since jiffies uses a simple TICK_NSEC multiplier
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
23 * larger can result in overflows. TICK_NSEC grows as HZ
24 * shrinks, so values greater than 8 overflow 32bits when
25 * HZ=100.
26 */
27#if HZ < 34
28#define JIFFIES_SHIFT 6
29#elif HZ < 67
30#define JIFFIES_SHIFT 7
31#else
32#define JIFFIES_SHIFT 8
33#endif
34
35static u64 jiffies_read(struct clocksource *cs)
36{
37 return (u64) jiffies;
38}
39
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 */
51static struct clocksource clocksource_jiffies = {
52 .name = "jiffies",
53 .rating = 1, /* lowest valid rating*/
54 .read = jiffies_read,
55 .mask = CLOCKSOURCE_MASK(32),
56 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
57 .shift = JIFFIES_SHIFT,
58 .max_cycles = 10,
59};
60
61__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
62__cacheline_aligned_in_smp seqcount_t jiffies_seq;
63
64#if (BITS_PER_LONG < 64)
65u64 get_jiffies_64(void)
66{
67 unsigned int seq;
68 u64 ret;
69
70 do {
71 seq = read_seqcount_begin(&jiffies_seq);
72 ret = jiffies_64;
73 } while (read_seqcount_retry(&jiffies_seq, seq));
74 return ret;
75}
76EXPORT_SYMBOL(get_jiffies_64);
77#endif
78
79EXPORT_SYMBOL(jiffies);
80
81static int __init init_jiffies_clocksource(void)
82{
83 return __clocksource_register(&clocksource_jiffies);
84}
85
86core_initcall(init_jiffies_clocksource);
87
88struct clocksource * __init __weak clocksource_default_clock(void)
89{
90 return &clocksource_jiffies;
91}
92
93static struct clocksource refined_jiffies;
94
95int register_refined_jiffies(long cycles_per_second)
96{
97 u64 nsec_per_tick, shift_hz;
98 long cycles_per_tick;
99
100
101
102 refined_jiffies = clocksource_jiffies;
103 refined_jiffies.name = "refined-jiffies";
104 refined_jiffies.rating++;
105
106 /* Calc cycles per tick */
107 cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
108 /* shift_hz stores hz<<8 for extra accuracy */
109 shift_hz = (u64)cycles_per_second << 8;
110 shift_hz += cycles_per_tick/2;
111 do_div(shift_hz, cycles_per_tick);
112 /* Calculate nsec_per_tick using shift_hz */
113 nsec_per_tick = (u64)NSEC_PER_SEC << 8;
114 nsec_per_tick += (u32)shift_hz/2;
115 do_div(nsec_per_tick, (u32)shift_hz);
116
117 refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
118
119 __clocksource_register(&refined_jiffies);
120 return 0;
121}