1 /* 2 * linux/include/linux/timecounter.h 3 * 4 * based on code that migrated away from 5 * linux/include/linux/clocksource.h 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License as published by 9 * the Free Software Foundation; either version 2 of the License, or 10 * (at your option) any later version. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 */ 17 #ifndef _LINUX_TIMECOUNTER_H 18 #define _LINUX_TIMECOUNTER_H 19 20 #include <linux/types.h> 21 22 /** 23 * struct cyclecounter - hardware abstraction for a free running counter 24 * Provides completely state-free accessors to the underlying hardware. 25 * Depending on which hardware it reads, the cycle counter may wrap 26 * around quickly. Locking rules (if necessary) have to be defined 27 * by the implementor and user of specific instances of this API. 28 * 29 * @read: returns the current cycle value 30 * @mask: bitmask for two's complement 31 * subtraction of non 64 bit counters, 32 * see CLOCKSOURCE_MASK() helper macro 33 * @mult: cycle to nanosecond multiplier 34 * @shift: cycle to nanosecond divisor (power of two) 35 */ 36 struct cyclecounter { 37 cycle_t (*read)(const struct cyclecounter *cc); 38 cycle_t mask; 39 u32 mult; 40 u32 shift; 41 }; 42 43 /** 44 * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds 45 * Contains the state needed by timecounter_read() to detect 46 * cycle counter wrap around. Initialize with 47 * timecounter_init(). Also used to convert cycle counts into the 48 * corresponding nanosecond counts with timecounter_cyc2time(). Users 49 * of this code are responsible for initializing the underlying 50 * cycle counter hardware, locking issues and reading the time 51 * more often than the cycle counter wraps around. The nanosecond 52 * counter will only wrap around after ~585 years. 53 * 54 * @cc: the cycle counter used by this instance 55 * @cycle_last: most recent cycle counter value seen by 56 * timecounter_read() 57 * @nsec: continuously increasing count 58 * @mask: bit mask for maintaining the 'frac' field 59 * @frac: accumulated fractional nanoseconds 60 */ 61 struct timecounter { 62 const struct cyclecounter *cc; 63 cycle_t cycle_last; 64 u64 nsec; 65 u64 mask; 66 u64 frac; 67 }; 68 69 /** 70 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds 71 * @cc: Pointer to cycle counter. 72 * @cycles: Cycles 73 * @mask: bit mask for maintaining the 'frac' field 74 * @frac: pointer to storage for the fractional nanoseconds. 75 */ 76 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc, 77 cycle_t cycles, u64 mask, u64 *frac) 78 { 79 u64 ns = (u64) cycles; 80 81 ns = (ns * cc->mult) + *frac; 82 *frac = ns & mask; 83 return ns >> cc->shift; 84 } 85 86 /** 87 * timecounter_adjtime - Shifts the time of the clock. 88 * @delta: Desired change in nanoseconds. 89 */ 90 static inline void timecounter_adjtime(struct timecounter *tc, s64 delta) 91 { 92 tc->nsec += delta; 93 } 94 95 /** 96 * timecounter_init - initialize a time counter 97 * @tc: Pointer to time counter which is to be initialized/reset 98 * @cc: A cycle counter, ready to be used. 99 * @start_tstamp: Arbitrary initial time stamp. 100 * 101 * After this call the current cycle register (roughly) corresponds to 102 * the initial time stamp. Every call to timecounter_read() increments 103 * the time stamp counter by the number of elapsed nanoseconds. 104 */ 105 extern void timecounter_init(struct timecounter *tc, 106 const struct cyclecounter *cc, 107 u64 start_tstamp); 108 109 /** 110 * timecounter_read - return nanoseconds elapsed since timecounter_init() 111 * plus the initial time stamp 112 * @tc: Pointer to time counter. 113 * 114 * In other words, keeps track of time since the same epoch as 115 * the function which generated the initial time stamp. 116 */ 117 extern u64 timecounter_read(struct timecounter *tc); 118 119 /** 120 * timecounter_cyc2time - convert a cycle counter to same 121 * time base as values returned by 122 * timecounter_read() 123 * @tc: Pointer to time counter. 124 * @cycle_tstamp: a value returned by tc->cc->read() 125 * 126 * Cycle counts that are converted correctly as long as they 127 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count], 128 * with "max cycle count" == cs->mask+1. 129 * 130 * This allows conversion of cycle counter values which were generated 131 * in the past. 132 */ 133 extern u64 timecounter_cyc2time(struct timecounter *tc, 134 cycle_t cycle_tstamp); 135 136 #endif 137