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-rw-r--r--include/linux/clocksource.h101
1 files changed, 101 insertions, 0 deletions
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index f88d32f8ff7c..573819ef4cc0 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -22,8 +22,109 @@ typedef u64 cycle_t;
22struct clocksource; 22struct clocksource;
23 23
24/** 24/**
25 * struct cyclecounter - hardware abstraction for a free running counter
26 * Provides completely state-free accessors to the underlying hardware.
27 * Depending on which hardware it reads, the cycle counter may wrap
28 * around quickly. Locking rules (if necessary) have to be defined
29 * by the implementor and user of specific instances of this API.
30 *
31 * @read: returns the current cycle value
32 * @mask: bitmask for two's complement
33 * subtraction of non 64 bit counters,
34 * see CLOCKSOURCE_MASK() helper macro
35 * @mult: cycle to nanosecond multiplier
36 * @shift: cycle to nanosecond divisor (power of two)
37 */
38struct cyclecounter {
39 cycle_t (*read)(const struct cyclecounter *cc);
40 cycle_t mask;
41 u32 mult;
42 u32 shift;
43};
44
45/**
46 * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
47 * Contains the state needed by timecounter_read() to detect
48 * cycle counter wrap around. Initialize with
49 * timecounter_init(). Also used to convert cycle counts into the
50 * corresponding nanosecond counts with timecounter_cyc2time(). Users
51 * of this code are responsible for initializing the underlying
52 * cycle counter hardware, locking issues and reading the time
53 * more often than the cycle counter wraps around. The nanosecond
54 * counter will only wrap around after ~585 years.
55 *
56 * @cc: the cycle counter used by this instance
57 * @cycle_last: most recent cycle counter value seen by
58 * timecounter_read()
59 * @nsec: continuously increasing count
60 */
61struct timecounter {
62 const struct cyclecounter *cc;
63 cycle_t cycle_last;
64 u64 nsec;
65};
66
67/**
68 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
69 * @tc: Pointer to cycle counter.
70 * @cycles: Cycles
71 *
72 * XXX - This could use some mult_lxl_ll() asm optimization. Same code
73 * as in cyc2ns, but with unsigned result.
74 */
75static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
76 cycle_t cycles)
77{
78 u64 ret = (u64)cycles;
79 ret = (ret * cc->mult) >> cc->shift;
80 return ret;
81}
82
83/**
84 * timecounter_init - initialize a time counter
85 * @tc: Pointer to time counter which is to be initialized/reset
86 * @cc: A cycle counter, ready to be used.
87 * @start_tstamp: Arbitrary initial time stamp.
88 *
89 * After this call the current cycle register (roughly) corresponds to
90 * the initial time stamp. Every call to timecounter_read() increments
91 * the time stamp counter by the number of elapsed nanoseconds.
92 */
93extern void timecounter_init(struct timecounter *tc,
94 const struct cyclecounter *cc,
95 u64 start_tstamp);
96
97/**
98 * timecounter_read - return nanoseconds elapsed since timecounter_init()
99 * plus the initial time stamp
100 * @tc: Pointer to time counter.
101 *
102 * In other words, keeps track of time since the same epoch as
103 * the function which generated the initial time stamp.
104 */
105extern u64 timecounter_read(struct timecounter *tc);
106
107/**
108 * timecounter_cyc2time - convert a cycle counter to same
109 * time base as values returned by
110 * timecounter_read()
111 * @tc: Pointer to time counter.
112 * @cycle: a value returned by tc->cc->read()
113 *
114 * Cycle counts that are converted correctly as long as they
115 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
116 * with "max cycle count" == cs->mask+1.
117 *
118 * This allows conversion of cycle counter values which were generated
119 * in the past.
120 */
121extern u64 timecounter_cyc2time(struct timecounter *tc,
122 cycle_t cycle_tstamp);
123
124/**
25 * struct clocksource - hardware abstraction for a free running counter 125 * struct clocksource - hardware abstraction for a free running counter
26 * Provides mostly state-free accessors to the underlying hardware. 126 * Provides mostly state-free accessors to the underlying hardware.
127 * This is the structure used for system time.
27 * 128 *
28 * @name: ptr to clocksource name 129 * @name: ptr to clocksource name
29 * @list: list head for registration 130 * @list: list head for registration