1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * linux/include/linux/timecounter.h
4 *
5 * based on code that migrated away from
6 * linux/include/linux/clocksource.h
7 */
8 #ifndef _LINUX_TIMECOUNTER_H
9 #define _LINUX_TIMECOUNTER_H
10
11 #include <linux/types.h>
12
13 /* simplify initialization of mask field */
14 #define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
15
16 /**
17 * struct cyclecounter - hardware abstraction for a free running counter
18 * Provides completely state-free accessors to the underlying hardware.
19 * Depending on which hardware it reads, the cycle counter may wrap
20 * around quickly. Locking rules (if necessary) have to be defined
21 * by the implementor and user of specific instances of this API.
22 *
23 * @read: returns the current cycle value
24 * @mask: bitmask for two's complement
25 * subtraction of non 64 bit counters,
26 * see CYCLECOUNTER_MASK() helper macro
27 * @mult: cycle to nanosecond multiplier
28 * @shift: cycle to nanosecond divisor (power of two)
29 */
30 struct cyclecounter {
31 u64 (*read)(const struct cyclecounter *cc);
32 u64 mask;
33 u32 mult;
34 u32 shift;
35 };
36
37 /**
38 * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
39 * Contains the state needed by timecounter_read() to detect
40 * cycle counter wrap around. Initialize with
41 * timecounter_init(). Also used to convert cycle counts into the
42 * corresponding nanosecond counts with timecounter_cyc2time(). Users
43 * of this code are responsible for initializing the underlying
44 * cycle counter hardware, locking issues and reading the time
45 * more often than the cycle counter wraps around. The nanosecond
46 * counter will only wrap around after ~585 years.
47 *
48 * @cc: the cycle counter used by this instance
49 * @cycle_last: most recent cycle counter value seen by
50 * timecounter_read()
51 * @nsec: continuously increasing count
52 * @mask: bit mask for maintaining the 'frac' field
53 * @frac: accumulated fractional nanoseconds
54 */
55 struct timecounter {
56 const struct cyclecounter *cc;
57 u64 cycle_last;
58 u64 nsec;
59 u64 mask;
60 u64 frac;
61 };
62
63 /**
64 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
65 * @cc: Pointer to cycle counter.
66 * @cycles: Cycles
67 * @mask: bit mask for maintaining the 'frac' field
68 * @frac: pointer to storage for the fractional nanoseconds.
69 */
70 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
71 u64 cycles, u64 mask, u64 *frac)
72 {
73 u64 ns = (u64) cycles;
74
75 ns = (ns * cc->mult) + *frac;
76 *frac = ns & mask;
77 return ns >> cc->shift;
78 }
79
80 /**
81 * timecounter_adjtime - Shifts the time of the clock.
82 * @delta: Desired change in nanoseconds.
83 */
84 static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
85 {
86 tc->nsec += delta;
87 }
88
89 /**
90 * timecounter_init - initialize a time counter
91 * @tc: Pointer to time counter which is to be initialized/reset
92 * @cc: A cycle counter, ready to be used.
93 * @start_tstamp: Arbitrary initial time stamp.
94 *
95 * After this call the current cycle register (roughly) corresponds to
96 * the initial time stamp. Every call to timecounter_read() increments
97 * the time stamp counter by the number of elapsed nanoseconds.
98 */
99 extern void timecounter_init(struct timecounter *tc,
100 const struct cyclecounter *cc,
101 u64 start_tstamp);
102
103 /**
104 * timecounter_read - return nanoseconds elapsed since timecounter_init()
105 * plus the initial time stamp
106 * @tc: Pointer to time counter.
107 *
108 * In other words, keeps track of time since the same epoch as
109 * the function which generated the initial time stamp.
110 */
111 extern u64 timecounter_read(struct timecounter *tc);
112
113 /**
114 * timecounter_cyc2time - convert a cycle counter to same
115 * time base as values returned by
116 * timecounter_read()
117 * @tc: Pointer to time counter.
118 * @cycle_tstamp: a value returned by tc->cc->read()
119 *
120 * Cycle counts that are converted correctly as long as they
121 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
122 * with "max cycle count" == cs->mask+1.
123 *
124 * This allows conversion of cycle counter values which were generated
125 * in the past.
126 */
127 extern u64 timecounter_cyc2time(struct timecounter *tc,
128 u64 cycle_tstamp);
129
130 #endif