/* * linux/include/linux/timecounter.h * * based on code that migrated away from * linux/include/linux/clocksource.h * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. */ #ifndef _LINUX_TIMECOUNTER_H #define _LINUX_TIMECOUNTER_H #include <linux/types.h> /* simplify initialization of mask field */ #define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1) /** * struct cyclecounter - hardware abstraction for a free running counter * Provides completely state-free accessors to the underlying hardware. * Depending on which hardware it reads, the cycle counter may wrap * around quickly. Locking rules (if necessary) have to be defined * by the implementor and user of specific instances of this API. * * @read: returns the current cycle value * @mask: bitmask for two's complement * subtraction of non 64 bit counters, * see CYCLECOUNTER_MASK() helper macro * @mult: cycle to nanosecond multiplier * @shift: cycle to nanosecond divisor (power of two) */ struct cyclecounter { u64 (*read)(const struct cyclecounter *cc); u64 mask; u32 mult; u32 shift; }; /** * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds * Contains the state needed by timecounter_read() to detect * cycle counter wrap around. Initialize with * timecounter_init(). Also used to convert cycle counts into the * corresponding nanosecond counts with timecounter_cyc2time(). Users * of this code are responsible for initializing the underlying * cycle counter hardware, locking issues and reading the time * more often than the cycle counter wraps around. The nanosecond * counter will only wrap around after ~585 years. * * @cc: the cycle counter used by this instance * @cycle_last: most recent cycle counter value seen by * timecounter_read() * @nsec: continuously increasing count * @mask: bit mask for maintaining the 'frac' field * @frac: accumulated fractional nanoseconds */ struct timecounter { const struct cyclecounter *cc; u64 cycle_last; u64 nsec; u64 mask; u64 frac; }; /** * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds * @cc: Pointer to cycle counter. * @cycles: Cycles * @mask: bit mask for maintaining the 'frac' field * @frac: pointer to storage for the fractional nanoseconds. */ static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc, u64 cycles, u64 mask, u64 *frac) { u64 ns = (u64) cycles; ns = (ns * cc->mult) + *frac; *frac = ns & mask; return ns >> cc->shift; } /** * timecounter_adjtime - Shifts the time of the clock. * @delta: Desired change in nanoseconds. */ static inline void timecounter_adjtime(struct timecounter *tc, s64 delta) { tc->nsec += delta; } /** * timecounter_init - initialize a time counter * @tc: Pointer to time counter which is to be initialized/reset * @cc: A cycle counter, ready to be used. * @start_tstamp: Arbitrary initial time stamp. * * After this call the current cycle register (roughly) corresponds to * the initial time stamp. Every call to timecounter_read() increments * the time stamp counter by the number of elapsed nanoseconds. */ extern void timecounter_init(struct timecounter *tc, const struct cyclecounter *cc, u64 start_tstamp); /** * timecounter_read - return nanoseconds elapsed since timecounter_init() * plus the initial time stamp * @tc: Pointer to time counter. * * In other words, keeps track of time since the same epoch as * the function which generated the initial time stamp. */ extern u64 timecounter_read(struct timecounter *tc); /** * timecounter_cyc2time - convert a cycle counter to same * time base as values returned by * timecounter_read() * @tc: Pointer to time counter. * @cycle_tstamp: a value returned by tc->cc->read() * * Cycle counts that are converted correctly as long as they * fall into the interval [-1/2 max cycle count, +1/2 max cycle count], * with "max cycle count" == cs->mask+1. * * This allows conversion of cycle counter values which were generated * in the past. */ extern u64 timecounter_cyc2time(struct timecounter *tc, u64 cycle_tstamp); #endif