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1/***********************************************************************
2* linux/kernel/time/jiffies.c
3*
4* This file contains the jiffies based clocksource.
5*
6* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
7*
8* This program is free software; you can redistribute it and/or modify
9* it under the terms of the GNU General Public License as published by
10* the Free Software Foundation; either version 2 of the License, or
11* (at your option) any later version.
12*
13* This program is distributed in the hope that it will be useful,
14* but WITHOUT ANY WARRANTY; without even the implied warranty of
15* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16* GNU General Public License for more details.
17*
18* You should have received a copy of the GNU General Public License
19* along with this program; if not, write to the Free Software
20* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21*
22************************************************************************/
23#include <linux/clocksource.h>
24#include <linux/jiffies.h>
25#include <linux/module.h>
26#include <linux/init.h>
27
28#include "tick-internal.h"
29
30/* The Jiffies based clocksource is the lowest common
31 * denominator clock source which should function on
32 * all systems. It has the same coarse resolution as
33 * the timer interrupt frequency HZ and it suffers
34 * inaccuracies caused by missed or lost timer
35 * interrupts and the inability for the timer
36 * interrupt hardware to accuratly tick at the
37 * requested HZ value. It is also not recommended
38 * for "tick-less" systems.
39 */
40#define NSEC_PER_JIFFY ((NSEC_PER_SEC+HZ/2)/HZ)
41
42/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
43 * conversion, the .shift value could be zero. However
44 * this would make NTP adjustments impossible as they are
45 * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
46 * shift both the nominator and denominator the same
47 * amount, and give ntp adjustments in units of 1/2^8
48 *
49 * The value 8 is somewhat carefully chosen, as anything
50 * larger can result in overflows. NSEC_PER_JIFFY grows as
51 * HZ shrinks, so values greater than 8 overflow 32bits when
52 * HZ=100.
53 */
54#if HZ < 34
55#define JIFFIES_SHIFT 6
56#elif HZ < 67
57#define JIFFIES_SHIFT 7
58#else
59#define JIFFIES_SHIFT 8
60#endif
61
62static cycle_t jiffies_read(struct clocksource *cs)
63{
64 return (cycle_t) jiffies;
65}
66
67static struct clocksource clocksource_jiffies = {
68 .name = "jiffies",
69 .rating = 1, /* lowest valid rating*/
70 .read = jiffies_read,
71 .mask = 0xffffffff, /*32bits*/
72 .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
73 .shift = JIFFIES_SHIFT,
74};
75
76__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
77
78#if (BITS_PER_LONG < 64)
79u64 get_jiffies_64(void)
80{
81 unsigned long seq;
82 u64 ret;
83
84 do {
85 seq = read_seqbegin(&jiffies_lock);
86 ret = jiffies_64;
87 } while (read_seqretry(&jiffies_lock, seq));
88 return ret;
89}
90EXPORT_SYMBOL(get_jiffies_64);
91#endif
92
93EXPORT_SYMBOL(jiffies);
94
95static int __init init_jiffies_clocksource(void)
96{
97 return clocksource_register(&clocksource_jiffies);
98}
99
100core_initcall(init_jiffies_clocksource);
101
102struct clocksource * __init __weak clocksource_default_clock(void)
103{
104 return &clocksource_jiffies;
105}
106
107struct clocksource refined_jiffies;
108
109int register_refined_jiffies(long cycles_per_second)
110{
111 u64 nsec_per_tick, shift_hz;
112 long cycles_per_tick;
113
114
115
116 refined_jiffies = clocksource_jiffies;
117 refined_jiffies.name = "refined-jiffies";
118 refined_jiffies.rating++;
119
120 /* Calc cycles per tick */
121 cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
122 /* shift_hz stores hz<<8 for extra accuracy */
123 shift_hz = (u64)cycles_per_second << 8;
124 shift_hz += cycles_per_tick/2;
125 do_div(shift_hz, cycles_per_tick);
126 /* Calculate nsec_per_tick using shift_hz */
127 nsec_per_tick = (u64)NSEC_PER_SEC << 8;
128 nsec_per_tick += (u32)shift_hz/2;
129 do_div(nsec_per_tick, (u32)shift_hz);
130
131 refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
132
133 clocksource_register(&refined_jiffies);
134 return 0;
135}
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
16static 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 */
32static 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)
48u64 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}
59EXPORT_SYMBOL(get_jiffies_64);
60#endif
61
62EXPORT_SYMBOL(jiffies);
63
64static int __init init_jiffies_clocksource(void)
65{
66 return __clocksource_register(&clocksource_jiffies);
67}
68
69core_initcall(init_jiffies_clocksource);
70
71struct clocksource * __init __weak clocksource_default_clock(void)
72{
73 return &clocksource_jiffies;
74}
75
76static struct clocksource refined_jiffies;
77
78int 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}