// 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,
                      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);