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Thomas Gleixner35728b82018-10-31 19:21:09 +01001// SPDX-License-Identifier: GPL-2.0+
Thomas Gleixner6c7811c2018-10-31 19:21:12 +01002/*
3 * This file contains the jiffies based clocksource.
4 *
5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6 */
john stultz734efb42006-06-26 00:25:05 -07007#include <linux/clocksource.h>
8#include <linux/jiffies.h>
Torben Hohnfbad1ea2011-01-27 15:59:00 +01009#include <linux/module.h>
john stultz734efb42006-06-26 00:25:05 -070010#include <linux/init.h>
11
Thomas Gleixnerbfb83b22015-03-25 13:06:04 +010012#include "timekeeping.h"
Torben Hohne2830b52011-01-27 16:00:32 +010013
john stultz734efb42006-06-26 00:25:05 -070014
Frederic Weisbecker93825f22017-01-31 04:09:16 +010015/* Since jiffies uses a simple TICK_NSEC multiplier
john stultz734efb42006-06-26 00:25:05 -070016 * 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
Frederic Weisbecker93825f22017-01-31 04:09:16 +010023 * larger can result in overflows. TICK_NSEC grows as HZ
24 * shrinks, so values greater than 8 overflow 32bits when
john stultz734efb42006-06-26 00:25:05 -070025 * HZ=100.
26 */
Mikulas Patocka80d767d2014-01-24 16:41:36 -050027#if HZ < 34
28#define JIFFIES_SHIFT 6
29#elif HZ < 67
30#define JIFFIES_SHIFT 7
31#else
john stultz734efb42006-06-26 00:25:05 -070032#define JIFFIES_SHIFT 8
Mikulas Patocka80d767d2014-01-24 16:41:36 -050033#endif
john stultz734efb42006-06-26 00:25:05 -070034
Thomas Gleixnera5a1d1c2016-12-21 20:32:01 +010035static u64 jiffies_read(struct clocksource *cs)
john stultz734efb42006-06-26 00:25:05 -070036{
Thomas Gleixnera5a1d1c2016-12-21 20:32:01 +010037 return (u64) jiffies;
john stultz734efb42006-06-26 00:25:05 -070038}
39
Frederic Weisbecker93825f22017-01-31 04:09:16 +010040/*
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 */
Lars-Peter Clausenf95a9852012-10-18 11:34:41 +020051static struct clocksource clocksource_jiffies = {
john stultz734efb42006-06-26 00:25:05 -070052 .name = "jiffies",
john stultz3f4a0b92006-10-17 00:09:32 -070053 .rating = 1, /* lowest valid rating*/
john stultz734efb42006-06-26 00:25:05 -070054 .read = jiffies_read,
Alexander Kuleshov232d2632016-02-26 19:14:14 -080055 .mask = CLOCKSOURCE_MASK(32),
Frederic Weisbecker93825f22017-01-31 04:09:16 +010056 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
john stultz734efb42006-06-26 00:25:05 -070057 .shift = JIFFIES_SHIFT,
John Stultz3c17ad12015-03-11 21:16:32 -070058 .max_cycles = 10,
john stultz734efb42006-06-26 00:25:05 -070059};
60
John Stultzd6ad4182012-02-28 16:50:11 -080061__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
62
Torben Hohnfbad1ea2011-01-27 15:59:00 +010063#if (BITS_PER_LONG < 64)
64u64 get_jiffies_64(void)
65{
66 unsigned long seq;
67 u64 ret;
68
69 do {
John Stultzd6ad4182012-02-28 16:50:11 -080070 seq = read_seqbegin(&jiffies_lock);
Torben Hohnfbad1ea2011-01-27 15:59:00 +010071 ret = jiffies_64;
John Stultzd6ad4182012-02-28 16:50:11 -080072 } while (read_seqretry(&jiffies_lock, seq));
Torben Hohnfbad1ea2011-01-27 15:59:00 +010073 return ret;
74}
75EXPORT_SYMBOL(get_jiffies_64);
76#endif
77
78EXPORT_SYMBOL(jiffies);
79
john stultz734efb42006-06-26 00:25:05 -070080static int __init init_jiffies_clocksource(void)
81{
John Stultzf8935982015-03-11 21:16:37 -070082 return __clocksource_register(&clocksource_jiffies);
john stultz734efb42006-06-26 00:25:05 -070083}
84
john stultz98de9e32007-04-04 19:08:24 -070085core_initcall(init_jiffies_clocksource);
Martin Schwidefskyf1b82742009-08-14 15:47:21 +020086
87struct clocksource * __init __weak clocksource_default_clock(void)
88{
89 return &clocksource_jiffies;
90}
John Stultzb3c869d2012-09-04 12:42:27 -040091
92struct clocksource refined_jiffies;
93
94int 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 */
Frederic Weisbeckerfa3aa7a2017-03-07 10:55:34 +0100112 nsec_per_tick = (u64)NSEC_PER_SEC << 8;
John Stultzb3c869d2012-09-04 12:42:27 -0400113 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
John Stultzf8935982015-03-11 21:16:37 -0700118 __clocksource_register(&refined_jiffies);
John Stultzb3c869d2012-09-04 12:42:27 -0400119 return 0;
120}