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 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 */ 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 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 */ 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 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