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1/*
2 * linux/kernel/time/timecounter.c
3 *
4 * based on code that migrated away from
5 * linux/kernel/time/clocksource.c
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 */
17
18#include <linux/export.h>
19#include <linux/timecounter.h>
20
21void timecounter_init(struct timecounter *tc,
22 const struct cyclecounter *cc,
23 u64 start_tstamp)
24{
25 tc->cc = cc;
26 tc->cycle_last = cc->read(cc);
27 tc->nsec = start_tstamp;
28 tc->mask = (1ULL << cc->shift) - 1;
29 tc->frac = 0;
30}
31EXPORT_SYMBOL_GPL(timecounter_init);
32
33/**
34 * timecounter_read_delta - get nanoseconds since last call of this function
35 * @tc: Pointer to time counter
36 *
37 * When the underlying cycle counter runs over, this will be handled
38 * correctly as long as it does not run over more than once between
39 * calls.
40 *
41 * The first call to this function for a new time counter initializes
42 * the time tracking and returns an undefined result.
43 */
44static u64 timecounter_read_delta(struct timecounter *tc)
45{
46 u64 cycle_now, cycle_delta;
47 u64 ns_offset;
48
49 /* read cycle counter: */
50 cycle_now = tc->cc->read(tc->cc);
51
52 /* calculate the delta since the last timecounter_read_delta(): */
53 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
54
55 /* convert to nanoseconds: */
56 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta,
57 tc->mask, &tc->frac);
58
59 /* update time stamp of timecounter_read_delta() call: */
60 tc->cycle_last = cycle_now;
61
62 return ns_offset;
63}
64
65u64 timecounter_read(struct timecounter *tc)
66{
67 u64 nsec;
68
69 /* increment time by nanoseconds since last call */
70 nsec = timecounter_read_delta(tc);
71 nsec += tc->nsec;
72 tc->nsec = nsec;
73
74 return nsec;
75}
76EXPORT_SYMBOL_GPL(timecounter_read);
77
78/*
79 * This is like cyclecounter_cyc2ns(), but it is used for computing a
80 * time previous to the time stored in the cycle counter.
81 */
82static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
83 u64 cycles, u64 mask, u64 frac)
84{
85 u64 ns = (u64) cycles;
86
87 ns = ((ns * cc->mult) - frac) >> cc->shift;
88
89 return ns;
90}
91
92u64 timecounter_cyc2time(struct timecounter *tc,
93 u64 cycle_tstamp)
94{
95 u64 delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
96 u64 nsec = tc->nsec, frac = tc->frac;
97
98 /*
99 * Instead of always treating cycle_tstamp as more recent
100 * than tc->cycle_last, detect when it is too far in the
101 * future and treat it as old time stamp instead.
102 */
103 if (delta > tc->cc->mask / 2) {
104 delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
105 nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
106 } else {
107 nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
108 }
109
110 return nsec;
111}
112EXPORT_SYMBOL_GPL(timecounter_cyc2time);
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Based on clocksource code. See commit 74d23cc704d1
4 */
5#include <linux/export.h>
6#include <linux/timecounter.h>
7
8void timecounter_init(struct timecounter *tc,
9 const struct cyclecounter *cc,
10 u64 start_tstamp)
11{
12 tc->cc = cc;
13 tc->cycle_last = cc->read(cc);
14 tc->nsec = start_tstamp;
15 tc->mask = (1ULL << cc->shift) - 1;
16 tc->frac = 0;
17}
18EXPORT_SYMBOL_GPL(timecounter_init);
19
20/**
21 * timecounter_read_delta - get nanoseconds since last call of this function
22 * @tc: Pointer to time counter
23 *
24 * When the underlying cycle counter runs over, this will be handled
25 * correctly as long as it does not run over more than once between
26 * calls.
27 *
28 * The first call to this function for a new time counter initializes
29 * the time tracking and returns an undefined result.
30 */
31static u64 timecounter_read_delta(struct timecounter *tc)
32{
33 u64 cycle_now, cycle_delta;
34 u64 ns_offset;
35
36 /* read cycle counter: */
37 cycle_now = tc->cc->read(tc->cc);
38
39 /* calculate the delta since the last timecounter_read_delta(): */
40 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
41
42 /* convert to nanoseconds: */
43 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta,
44 tc->mask, &tc->frac);
45
46 /* update time stamp of timecounter_read_delta() call: */
47 tc->cycle_last = cycle_now;
48
49 return ns_offset;
50}
51
52u64 timecounter_read(struct timecounter *tc)
53{
54 u64 nsec;
55
56 /* increment time by nanoseconds since last call */
57 nsec = timecounter_read_delta(tc);
58 nsec += tc->nsec;
59 tc->nsec = nsec;
60
61 return nsec;
62}
63EXPORT_SYMBOL_GPL(timecounter_read);
64
65/*
66 * This is like cyclecounter_cyc2ns(), but it is used for computing a
67 * time previous to the time stored in the cycle counter.
68 */
69static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
70 u64 cycles, u64 mask, u64 frac)
71{
72 u64 ns = (u64) cycles;
73
74 ns = ((ns * cc->mult) - frac) >> cc->shift;
75
76 return ns;
77}
78
79u64 timecounter_cyc2time(const struct timecounter *tc,
80 u64 cycle_tstamp)
81{
82 u64 delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
83 u64 nsec = tc->nsec, frac = tc->frac;
84
85 /*
86 * Instead of always treating cycle_tstamp as more recent
87 * than tc->cycle_last, detect when it is too far in the
88 * future and treat it as old time stamp instead.
89 */
90 if (delta > tc->cc->mask / 2) {
91 delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
92 nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
93 } else {
94 nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
95 }
96
97 return nsec;
98}
99EXPORT_SYMBOL_GPL(timecounter_cyc2time);