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(const struct timecounter *tc, |
128 | u64 cycle_tstamp); |
129 | |
130 | #endif |
131 | |