1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Based on clocksource code. See commit 74d23cc704d1
4 */
5 #include <linux/export.h>
6 #include <linux/timecounter.h>
7
timecounter_init(struct timecounter * tc,const struct cyclecounter * cc,u64 start_tstamp)8 void timecounter_init(struct timecounter *tc,
9 const struct cyclecounter *cc,
10 u64 start_tstamp)
11 {
12 tc->cc = cc;
13 tc->cycle_last = cc->read(cc);
14 tc->nsec = start_tstamp;
15 tc->mask = (1ULL << cc->shift) - 1;
16 tc->frac = 0;
17 }
18 EXPORT_SYMBOL_GPL(timecounter_init);
19
20 /**
21 * timecounter_read_delta - get nanoseconds since last call of this function
22 * @tc: Pointer to time counter
23 *
24 * When the underlying cycle counter runs over, this will be handled
25 * correctly as long as it does not run over more than once between
26 * calls.
27 *
28 * The first call to this function for a new time counter initializes
29 * the time tracking and returns an undefined result.
30 */
timecounter_read_delta(struct timecounter * tc)31 static u64 timecounter_read_delta(struct timecounter *tc)
32 {
33 u64 cycle_now, cycle_delta;
34 u64 ns_offset;
35
36 /* read cycle counter: */
37 cycle_now = tc->cc->read(tc->cc);
38
39 /* calculate the delta since the last timecounter_read_delta(): */
40 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
41
42 /* convert to nanoseconds: */
43 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta,
44 tc->mask, &tc->frac);
45
46 /* update time stamp of timecounter_read_delta() call: */
47 tc->cycle_last = cycle_now;
48
49 return ns_offset;
50 }
51
timecounter_read(struct timecounter * tc)52 u64 timecounter_read(struct timecounter *tc)
53 {
54 u64 nsec;
55
56 /* increment time by nanoseconds since last call */
57 nsec = timecounter_read_delta(tc);
58 nsec += tc->nsec;
59 tc->nsec = nsec;
60
61 return nsec;
62 }
63 EXPORT_SYMBOL_GPL(timecounter_read);
64
65 /*
66 * This is like cyclecounter_cyc2ns(), but it is used for computing a
67 * time previous to the time stored in the cycle counter.
68 */
cc_cyc2ns_backwards(const struct cyclecounter * cc,u64 cycles,u64 mask,u64 frac)69 static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
70 u64 cycles, u64 mask, u64 frac)
71 {
72 u64 ns = (u64) cycles;
73
74 ns = ((ns * cc->mult) - frac) >> cc->shift;
75
76 return ns;
77 }
78
timecounter_cyc2time(struct timecounter * tc,u64 cycle_tstamp)79 u64 timecounter_cyc2time(struct timecounter *tc,
80 u64 cycle_tstamp)
81 {
82 u64 delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
83 u64 nsec = tc->nsec, frac = tc->frac;
84
85 /*
86 * Instead of always treating cycle_tstamp as more recent
87 * than tc->cycle_last, detect when it is too far in the
88 * future and treat it as old time stamp instead.
89 */
90 if (delta > tc->cc->mask / 2) {
91 delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
92 nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
93 } else {
94 nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
95 }
96
97 return nsec;
98 }
99 EXPORT_SYMBOL_GPL(timecounter_cyc2time);
100
