1/*
2 * linux/include/linux/timecounter.h
3 *
4 * based on code that migrated away from
5 * linux/include/linux/clocksource.h
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#ifndef _LINUX_TIMECOUNTER_H
18#define _LINUX_TIMECOUNTER_H
19
20#include <linux/types.h>
21
22/* simplify initialization of mask field */
23#define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
24
25/**
26 * struct cyclecounter - hardware abstraction for a free running counter
27 * Provides completely state-free accessors to the underlying hardware.
28 * Depending on which hardware it reads, the cycle counter may wrap
29 * around quickly. Locking rules (if necessary) have to be defined
30 * by the implementor and user of specific instances of this API.
31 *
32 * @read: returns the current cycle value
33 * @mask: bitmask for two's complement
34 * subtraction of non 64 bit counters,
35 * see CYCLECOUNTER_MASK() helper macro
36 * @mult: cycle to nanosecond multiplier
37 * @shift: cycle to nanosecond divisor (power of two)
38 */
39struct cyclecounter {
40 u64 (*read)(const struct cyclecounter *cc);
41 u64 mask;
42 u32 mult;
43 u32 shift;
44};
45
46/**
47 * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
48 * Contains the state needed by timecounter_read() to detect
49 * cycle counter wrap around. Initialize with
50 * timecounter_init(). Also used to convert cycle counts into the
51 * corresponding nanosecond counts with timecounter_cyc2time(). Users
52 * of this code are responsible for initializing the underlying
53 * cycle counter hardware, locking issues and reading the time
54 * more often than the cycle counter wraps around. The nanosecond
55 * counter will only wrap around after ~585 years.
56 *
57 * @cc: the cycle counter used by this instance
58 * @cycle_last: most recent cycle counter value seen by
59 * timecounter_read()
60 * @nsec: continuously increasing count
61 * @mask: bit mask for maintaining the 'frac' field
62 * @frac: accumulated fractional nanoseconds
63 */
64struct timecounter {
65 const struct cyclecounter *cc;
66 u64 cycle_last;
67 u64 nsec;
68 u64 mask;
69 u64 frac;
70};
71
72/**
73 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
74 * @cc: Pointer to cycle counter.
75 * @cycles: Cycles
76 * @mask: bit mask for maintaining the 'frac' field
77 * @frac: pointer to storage for the fractional nanoseconds.
78 */
79static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
80 u64 cycles, u64 mask, u64 *frac)
81{
82 u64 ns = (u64) cycles;
83
84 ns = (ns * cc->mult) + *frac;
85 *frac = ns & mask;
86 return ns >> cc->shift;
87}
88
89/**
90 * timecounter_adjtime - Shifts the time of the clock.
91 * @delta: Desired change in nanoseconds.
92 */
93static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
94{
95 tc->nsec += delta;
96}
97
98/**
99 * timecounter_init - initialize a time counter
100 * @tc: Pointer to time counter which is to be initialized/reset
101 * @cc: A cycle counter, ready to be used.
102 * @start_tstamp: Arbitrary initial time stamp.
103 *
104 * After this call the current cycle register (roughly) corresponds to
105 * the initial time stamp. Every call to timecounter_read() increments
106 * the time stamp counter by the number of elapsed nanoseconds.
107 */
108extern void timecounter_init(struct timecounter *tc,
109 const struct cyclecounter *cc,
110 u64 start_tstamp);
111
112/**
113 * timecounter_read - return nanoseconds elapsed since timecounter_init()
114 * plus the initial time stamp
115 * @tc: Pointer to time counter.
116 *
117 * In other words, keeps track of time since the same epoch as
118 * the function which generated the initial time stamp.
119 */
120extern u64 timecounter_read(struct timecounter *tc);
121
122/**
123 * timecounter_cyc2time - convert a cycle counter to same
124 * time base as values returned by
125 * timecounter_read()
126 * @tc: Pointer to time counter.
127 * @cycle_tstamp: a value returned by tc->cc->read()
128 *
129 * Cycle counts that are converted correctly as long as they
130 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
131 * with "max cycle count" == cs->mask+1.
132 *
133 * This allows conversion of cycle counter values which were generated
134 * in the past.
135 */
136extern u64 timecounter_cyc2time(struct timecounter *tc,
137 u64 cycle_tstamp);
138
139#endif
140