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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165/* SPDX-License-Identifier: GPL-2.0-or-later *//* * linux/include/linux/timecounter.h * * based on code that migrated away from * linux/include/linux/clocksource.h */#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)(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 { 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. * * Returns: cycle counter cycles converted to 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. * @tc: The &struct timecounter to adjust * @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, 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. * * Returns: nanoseconds since the initial time stamp */extern u64 timecounter_read(struct timecounter *tc);
/* * This is like cyclecounter_cyc2ns(), but it is used for computing a * time previous to the time stored in the cycle counter. */static inline u64 cc_cyc2ns_backwards(const struct cyclecounter *cc, u64 cycles, u64 frac){ return ((cycles * cc->mult) - frac) >> cc->shift;}
/** * 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. * * Returns: cycle counter converted to nanoseconds since the initial time stamp */static inline u64 timecounter_cyc2time(const struct timecounter *tc, u64 cycle_tstamp){ const struct cyclecounter *cc = tc->cc; u64 delta = (cycle_tstamp - tc->cycle_last) & cc->mask; u64 nsec = tc->nsec, frac = tc->frac;
/* * Instead of always treating cycle_tstamp as more recent than * tc->cycle_last, detect when it is too far in the future and * treat it as old time stamp instead. */ if (unlikely(delta > cc->mask / 2)) { delta = (tc->cycle_last - cycle_tstamp) & cc->mask; nsec -= cc_cyc2ns_backwards(cc, delta, frac); } else { nsec += cyclecounter_cyc2ns(cc, delta, tc->mask, &frac); }
return nsec;}
#endif