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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 ((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
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#define JIFFIES_SHIFT 8
55
56static cycle_t jiffies_read(struct clocksource *cs)
57{
58 return (cycle_t) jiffies;
59}
60
61struct clocksource clocksource_jiffies = {
62 .name = "jiffies",
63 .rating = 1, /* lowest valid rating*/
64 .read = jiffies_read,
65 .mask = 0xffffffff, /*32bits*/
66 .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
67 .shift = JIFFIES_SHIFT,
68};
69
70#if (BITS_PER_LONG < 64)
71u64 get_jiffies_64(void)
72{
73 unsigned long seq;
74 u64 ret;
75
76 do {
77 seq = read_seqbegin(&xtime_lock);
78 ret = jiffies_64;
79 } while (read_seqretry(&xtime_lock, seq));
80 return ret;
81}
82EXPORT_SYMBOL(get_jiffies_64);
83#endif
84
85EXPORT_SYMBOL(jiffies);
86
87static int __init init_jiffies_clocksource(void)
88{
89 return clocksource_register(&clocksource_jiffies);
90}
91
92core_initcall(init_jiffies_clocksource);
93
94struct clocksource * __init __weak clocksource_default_clock(void)
95{
96 return &clocksource_jiffies;
97}
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 ((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
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#define JIFFIES_SHIFT 8
55
56static cycle_t jiffies_read(struct clocksource *cs)
57{
58 return (cycle_t) jiffies;
59}
60
61struct clocksource clocksource_jiffies = {
62 .name = "jiffies",
63 .rating = 1, /* lowest valid rating*/
64 .read = jiffies_read,
65 .mask = 0xffffffff, /*32bits*/
66 .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
67 .shift = JIFFIES_SHIFT,
68};
69
70#if (BITS_PER_LONG < 64)
71u64 get_jiffies_64(void)
72{
73 unsigned long seq;
74 u64 ret;
75
76 do {
77 seq = read_seqbegin(&xtime_lock);
78 ret = jiffies_64;
79 } while (read_seqretry(&xtime_lock, seq));
80 return ret;
81}
82EXPORT_SYMBOL(get_jiffies_64);
83#endif
84
85EXPORT_SYMBOL(jiffies);
86
87static int __init init_jiffies_clocksource(void)
88{
89 return clocksource_register(&clocksource_jiffies);
90}
91
92core_initcall(init_jiffies_clocksource);
93
94struct clocksource * __init __weak clocksource_default_clock(void)
95{
96 return &clocksource_jiffies;
97}