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) (cycle_t)((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 */
39 struct cyclecounter {
40 cycle_t (*read)(const struct cyclecounter *cc);
41 cycle_t 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 */
62 struct timecounter {
63 const struct cyclecounter *cc;
64 cycle_t cycle_last;
65 u64 nsec;
66 };
67
68 /**
69 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
70 * @cc: Pointer to cycle counter.
71 * @cycles: Cycles
72 *
73 * XXX - This could use some mult_lxl_ll() asm optimization. Same code
74 * as in cyc2ns, but with unsigned result.
75 */
cyclecounter_cyc2ns(const struct cyclecounter * cc,cycle_t cycles)76 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
77 cycle_t cycles)
78 {
79 u64 ret = (u64)cycles;
80 ret = (ret * cc->mult) >> cc->shift;
81 return ret;
82 }
83
84 /**
85 * timecounter_init - initialize a time counter
86 * @tc: Pointer to time counter which is to be initialized/reset
87 * @cc: A cycle counter, ready to be used.
88 * @start_tstamp: Arbitrary initial time stamp.
89 *
90 * After this call the current cycle register (roughly) corresponds to
91 * the initial time stamp. Every call to timecounter_read() increments
92 * the time stamp counter by the number of elapsed nanoseconds.
93 */
94 extern void timecounter_init(struct timecounter *tc,
95 const struct cyclecounter *cc,
96 u64 start_tstamp);
97
98 /**
99 * timecounter_read - return nanoseconds elapsed since timecounter_init()
100 * plus the initial time stamp
101 * @tc: Pointer to time counter.
102 *
103 * In other words, keeps track of time since the same epoch as
104 * the function which generated the initial time stamp.
105 */
106 extern u64 timecounter_read(struct timecounter *tc);
107
108 /**
109 * timecounter_cyc2time - convert a cycle counter to same
110 * time base as values returned by
111 * timecounter_read()
112 * @tc: Pointer to time counter.
113 * @cycle_tstamp: a value returned by tc->cc->read()
114 *
115 * Cycle counts that are converted correctly as long as they
116 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
117 * with "max cycle count" == cs->mask+1.
118 *
119 * This allows conversion of cycle counter values which were generated
120 * in the past.
121 */
122 extern u64 timecounter_cyc2time(struct timecounter *tc,
123 cycle_t cycle_tstamp);
124
125 #endif
126