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/*
* 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
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