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c942fddf | 1 | /* SPDX-License-Identifier: GPL-2.0-or-later */ |
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2 | /* |
3 | * linux/include/linux/timecounter.h | |
4 | * | |
5 | * based on code that migrated away from | |
6 | * linux/include/linux/clocksource.h | |
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7 | */ |
8 | #ifndef _LINUX_TIMECOUNTER_H | |
9 | #define _LINUX_TIMECOUNTER_H | |
10 | ||
11 | #include <linux/types.h> | |
12 | ||
1891172a | 13 | /* simplify initialization of mask field */ |
a5a1d1c2 | 14 | #define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1) |
1891172a | 15 | |
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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, | |
1891172a | 26 | * see CYCLECOUNTER_MASK() helper macro |
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27 | * @mult: cycle to nanosecond multiplier |
28 | * @shift: cycle to nanosecond divisor (power of two) | |
29 | */ | |
30 | struct cyclecounter { | |
a5a1d1c2 TG |
31 | u64 (*read)(const struct cyclecounter *cc); |
32 | u64 mask; | |
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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 | |
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52 | * @mask: bit mask for maintaining the 'frac' field |
53 | * @frac: accumulated fractional nanoseconds | |
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54 | */ |
55 | struct timecounter { | |
56 | const struct cyclecounter *cc; | |
a5a1d1c2 | 57 | u64 cycle_last; |
74d23cc7 | 58 | u64 nsec; |
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59 | u64 mask; |
60 | u64 frac; | |
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61 | }; |
62 | ||
63 | /** | |
64 | * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds | |
65 | * @cc: Pointer to cycle counter. | |
66 | * @cycles: Cycles | |
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67 | * @mask: bit mask for maintaining the 'frac' field |
68 | * @frac: pointer to storage for the fractional nanoseconds. | |
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69 | */ |
70 | static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc, | |
a5a1d1c2 | 71 | u64 cycles, u64 mask, u64 *frac) |
74d23cc7 | 72 | { |
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73 | u64 ns = (u64) cycles; |
74 | ||
75 | ns = (ns * cc->mult) + *frac; | |
76 | *frac = ns & mask; | |
77 | return ns >> cc->shift; | |
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78 | } |
79 | ||
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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 | ||
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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, | |
a5a1d1c2 | 128 | u64 cycle_tstamp); |
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129 | |
130 | #endif |