linux/kernel/time/timecounter.c
Marc Kleine-Budde 07ff4aed01 time/timecounter: Mark 1st argument of timecounter_cyc2time() as const
The timecounter is not modified in this function. Mark it as const.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210303103544.994855-1-mkl@pengutronix.de
2021-04-16 21:03:50 +02:00

100 lines
2.5 KiB
C

// SPDX-License-Identifier: GPL-2.0+
/*
* Based on clocksource code. See commit 74d23cc704d1
*/
#include <linux/export.h>
#include <linux/timecounter.h>
void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc,
u64 start_tstamp)
{
tc->cc = cc;
tc->cycle_last = cc->read(cc);
tc->nsec = start_tstamp;
tc->mask = (1ULL << cc->shift) - 1;
tc->frac = 0;
}
EXPORT_SYMBOL_GPL(timecounter_init);
/**
* timecounter_read_delta - get nanoseconds since last call of this function
* @tc: Pointer to time counter
*
* When the underlying cycle counter runs over, this will be handled
* correctly as long as it does not run over more than once between
* calls.
*
* The first call to this function for a new time counter initializes
* the time tracking and returns an undefined result.
*/
static u64 timecounter_read_delta(struct timecounter *tc)
{
u64 cycle_now, cycle_delta;
u64 ns_offset;
/* read cycle counter: */
cycle_now = tc->cc->read(tc->cc);
/* calculate the delta since the last timecounter_read_delta(): */
cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
/* convert to nanoseconds: */
ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta,
tc->mask, &tc->frac);
/* update time stamp of timecounter_read_delta() call: */
tc->cycle_last = cycle_now;
return ns_offset;
}
u64 timecounter_read(struct timecounter *tc)
{
u64 nsec;
/* increment time by nanoseconds since last call */
nsec = timecounter_read_delta(tc);
nsec += tc->nsec;
tc->nsec = nsec;
return nsec;
}
EXPORT_SYMBOL_GPL(timecounter_read);
/*
* This is like cyclecounter_cyc2ns(), but it is used for computing a
* time previous to the time stored in the cycle counter.
*/
static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
u64 cycles, u64 mask, u64 frac)
{
u64 ns = (u64) cycles;
ns = ((ns * cc->mult) - frac) >> cc->shift;
return ns;
}
u64 timecounter_cyc2time(const struct timecounter *tc,
u64 cycle_tstamp)
{
u64 delta = (cycle_tstamp - tc->cycle_last) & tc->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 (delta > tc->cc->mask / 2) {
delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
} else {
nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
}
return nsec;
}
EXPORT_SYMBOL_GPL(timecounter_cyc2time);