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Release 4.12 include/linux/timecounter.h

Directory: include/linux
 * 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
 * GNU General Public License for more details.


#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; }


Richard Cochran5798.28%266.67%
Thomas Gleixner11.72%133.33%

/** * 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; }


Richard Cochran21100.00%1100.00%

/** * 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

Overall Contributors

Richard Cochran19296.97%480.00%
Thomas Gleixner63.03%120.00%
Directory: include/linux
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