/* $NetBSD: kern_tc.c,v 1.80 2026/01/04 01:54:31 riastradh Exp $ */

/*-
 * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Andrew Doran.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*-
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
 * ---------------------------------------------------------------------------
 */

/*
 * https://papers.freebsd.org/2002/phk-timecounters.files/timecounter.pdf
 */

#include <sys/cdefs.h>
/* __FBSDID("$FreeBSD: src/sys/kern/kern_tc.c,v 1.166 2005/09/19 22:16:31 andre Exp $"); */
__KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.80 2026/01/04 01:54:31 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_ntp.h"
#endif

#include <sys/param.h>

#include <sys/atomic.h>
#include <sys/evcnt.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/reboot.h> /* XXX just to get AB_VERBOSE */
#include <sys/sdt.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#include <sys/timepps.h>
#include <sys/timetc.h>
#include <sys/timex.h>
#include <sys/xcall.h>

/*
 * A large step happens on boot.  This constant detects such steps.
 * It is relatively small so that ntp_update_second gets called enough
 * in the typical 'missed a couple of seconds' case, but doesn't loop
 * forever when the time step is large.
 */
#define LARGE_STEP      200

/*
 * Implement a dummy timecounter which we can use until we get a real one
 * in the air.  This allows the console and other early stuff to use
 * time services.
 */

static u_int
dummy_get_timecount(struct timecounter *tc)
{
        static u_int now;

        return ++now;
}

static struct timecounter dummy_timecounter = {
        .tc_get_timecount       = dummy_get_timecount,
        .tc_counter_mask        = ~0u,
        .tc_frequency           = 1000000,
        .tc_name                = "dummy",
        .tc_quality             = -1000000,
        .tc_priv                = NULL,
};

struct timehands {
        /* These fields must be initialized by the driver. */
        struct timecounter      *th_counter;     /* active timecounter */
        int64_t                 th_adjustment;   /* frequency adjustment */
                                                 /* (NTP/adjtime) */
        uint64_t                th_scale;        /* scale factor (counter */
                                                 /* tick->time) */
        uint64_t                th_offset_count; /* offset at last time */
                                                 /* update (tc_windup()) */
        struct bintime          th_offset;       /* bin (up)time at windup */
        struct timeval          th_microtime;    /* cached microtime */
        struct timespec         th_nanotime;     /* cached nanotime */
        /* Fields not to be copied in tc_windup start with th_generation. */
        volatile u_int          th_generation;   /* current generation */
        struct timehands        *th_next;        /* next timehand */
};

static struct timehands th0;
static struct timehands th9 = { .th_next = &th0, };
static struct timehands th8 = { .th_next = &th9, };
static struct timehands th7 = { .th_next = &th8, };
static struct timehands th6 = { .th_next = &th7, };
static struct timehands th5 = { .th_next = &th6, };
static struct timehands th4 = { .th_next = &th5, };
static struct timehands th3 = { .th_next = &th4, };
static struct timehands th2 = { .th_next = &th3, };
static struct timehands th1 = { .th_next = &th2, };
static struct timehands th0 = {
        .th_counter = &dummy_timecounter,
        .th_scale = (uint64_t)-1 / 1000000,
        .th_offset = { .sec = 1, .frac = 0 },
        .th_generation = 1,
        .th_next = &th1,
};

static struct timehands *volatile timehands = &th0;
struct timecounter *timecounter = &dummy_timecounter;
static struct timecounter *timecounters = &dummy_timecounter;

/* used by savecore(8) */
time_t time_second_legacy asm("time_second");

#ifdef __HAVE_ATOMIC64_LOADSTORE
volatile time_t time__second __cacheline_aligned = 1;
volatile time_t time__uptime __cacheline_aligned = 1;
#else
static volatile struct {
        uint32_t lo, hi;
} time__uptime32 __cacheline_aligned = {
        .lo = 1,
}, time__second32 __cacheline_aligned = {
        .lo = 1,
};
#endif

static struct {
        struct bintime bin;
        volatile unsigned gen;  /* even when stable, odd when changing */
} timebase __cacheline_aligned;

static int timestepwarnings;

kmutex_t timecounter_lock;
static u_int timecounter_mods;
static volatile int timecounter_removals = 1;
static u_int timecounter_bad;

#ifdef __HAVE_ATOMIC64_LOADSTORE

static inline void
setrealuptime(time_t second, time_t uptime)
{

        time_second_legacy = second;

        atomic_store_relaxed(&time__second, second);
        atomic_store_relaxed(&time__uptime, uptime);
}

#else

static inline void
setrealuptime(time_t second, time_t uptime)
{
        uint32_t seclo = second & 0xffffffff, sechi = second >> 32;
        uint32_t uplo = uptime & 0xffffffff, uphi = uptime >> 32;

        KDASSERT(mutex_owned(&timecounter_lock));

        time_second_legacy = second;

        /*
         * Fast path -- no wraparound, just updating the low bits, so
         * no need for seqlocked access.
         */
        if (__predict_true(sechi == time__second32.hi) &&
            __predict_true(uphi == time__uptime32.hi)) {
                atomic_store_relaxed(&time__second32.lo, seclo);
                atomic_store_relaxed(&time__uptime32.lo, uplo);
                return;
        }

        atomic_store_relaxed(&time__second32.hi, 0xffffffff);
        atomic_store_relaxed(&time__uptime32.hi, 0xffffffff);
        membar_producer();
        atomic_store_relaxed(&time__second32.lo, seclo);
        atomic_store_relaxed(&time__uptime32.lo, uplo);
        membar_producer();
        atomic_store_relaxed(&time__second32.hi, sechi);
        atomic_store_relaxed(&time__uptime32.hi, uphi);
}

time_t
getrealtime(void)
{
        uint32_t lo, hi;

        do {
                for (;;) {
                        hi = atomic_load_relaxed(&time__second32.hi);
                        if (__predict_true(hi != 0xffffffff))
                                break;
                        SPINLOCK_BACKOFF_HOOK;
                }
                membar_consumer();
                lo = atomic_load_relaxed(&time__second32.lo);
                membar_consumer();
        } while (hi != atomic_load_relaxed(&time__second32.hi));

        return ((time_t)hi << 32) | lo;
}

time_t
getuptime(void)
{
        uint32_t lo, hi;

        do {
                for (;;) {
                        hi = atomic_load_relaxed(&time__uptime32.hi);
                        if (__predict_true(hi != 0xffffffff))
                                break;
                        SPINLOCK_BACKOFF_HOOK;
                }
                membar_consumer();
                lo = atomic_load_relaxed(&time__uptime32.lo);
                membar_consumer();
        } while (hi != atomic_load_relaxed(&time__uptime32.hi));

        return ((time_t)hi << 32) | lo;
}

time_t
getboottime(void)
{

        return getrealtime() - getuptime();
}

uint32_t
getuptime32(void)
{

        return atomic_load_relaxed(&time__uptime32.lo);
}

#endif  /* !defined(__HAVE_ATOMIC64_LOADSTORE) */

/*
 * sysctl helper routine for kern.timercounter.hardware
 */
static int
sysctl_kern_timecounter_hardware(SYSCTLFN_ARGS)
{
        struct sysctlnode node;
        int error;
        char newname[MAX_TCNAMELEN];
        struct timecounter *newtc, *tc;

        tc = timecounter;

        strlcpy(newname, tc->tc_name, sizeof(newname));

        node = *rnode;
        node.sysctl_data = newname;
        node.sysctl_size = sizeof(newname);

        error = sysctl_lookup(SYSCTLFN_CALL(&node));

        if (error ||
            newp == NULL ||
            strncmp(newname, tc->tc_name, sizeof(newname)) == 0)
                return error;

        if (l != NULL && (error = kauth_authorize_system(l->l_cred,
            KAUTH_SYSTEM_TIME, KAUTH_REQ_SYSTEM_TIME_TIMECOUNTERS, newname,
            NULL, NULL)) != 0)
                return error;

        if (!cold)
                mutex_spin_enter(&timecounter_lock);
        error = SET_ERROR(EINVAL);
        for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) {
                if (strcmp(newname, newtc->tc_name) != 0)
                        continue;
                /* Warm up new timecounter. */
                (void)newtc->tc_get_timecount(newtc);
                (void)newtc->tc_get_timecount(newtc);
                timecounter = newtc;
                error = 0;
                break;
        }
        if (!cold)
                mutex_spin_exit(&timecounter_lock);
        return error;
}

static int
sysctl_kern_timecounter_choice(SYSCTLFN_ARGS)
{
        char buf[MAX_TCNAMELEN+48];
        char *where;
        const char *spc;
        struct timecounter *tc;
        size_t needed, left, slen;
        int error, mods;

        if (newp != NULL)
                return SET_ERROR(EPERM);
        if (namelen != 0)
                return SET_ERROR(EINVAL);

        mutex_spin_enter(&timecounter_lock);
 retry:
        spc = "";
        error = 0;
        needed = 0;
        left = *oldlenp;
        where = oldp;
        for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) {
                if (where == NULL) {
                        needed += sizeof(buf);  /* be conservative */
                } else {
                        slen = snprintf(buf, sizeof(buf), "%s%s(q=%d, f=%" PRId64
                                        " Hz)", spc, tc->tc_name, tc->tc_quality,
                                        tc->tc_frequency);
                        if (left < slen + 1)
                                break;
                        mods = timecounter_mods;
                        mutex_spin_exit(&timecounter_lock);
                        error = copyout(buf, where, slen + 1);
                        mutex_spin_enter(&timecounter_lock);
                        if (mods != timecounter_mods) {
                                goto retry;
                        }
                        spc = " ";
                        where += slen;
                        needed += slen;
                        left -= slen;
                }
        }
        mutex_spin_exit(&timecounter_lock);

        *oldlenp = needed;
        return error;
}

SYSCTL_SETUP(sysctl_timecounter_setup, "sysctl timecounter setup")
{
        const struct sysctlnode *node;

        sysctl_createv(clog, 0, NULL, &node,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "timecounter",
                       SYSCTL_DESCR("time counter information"),
                       NULL, 0, NULL, 0,
                       CTL_KERN, CTL_CREATE, CTL_EOL);

        if (node != NULL) {
                sysctl_createv(clog, 0, NULL, NULL,
                               CTLFLAG_PERMANENT,
                               CTLTYPE_STRING, "choice",
                               SYSCTL_DESCR("available counters"),
                               sysctl_kern_timecounter_choice, 0, NULL, 0,
                               CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);

                sysctl_createv(clog, 0, NULL, NULL,
                               CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                               CTLTYPE_STRING, "hardware",
                               SYSCTL_DESCR("currently active time counter"),
                               sysctl_kern_timecounter_hardware, 0, NULL, MAX_TCNAMELEN,
                               CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);

                sysctl_createv(clog, 0, NULL, NULL,
                               CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                               CTLTYPE_INT, "timestepwarnings",
                               SYSCTL_DESCR("log time steps"),
                               NULL, 0, &timestepwarnings, 0,
                               CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);
        }
}

#ifdef TC_COUNTERS
#define TC_STATS(name)                                                  \
static struct evcnt n##name =                                           \
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "timecounter", #name);     \
EVCNT_ATTACH_STATIC(n##name)
TC_STATS(binuptime);    TC_STATS(nanouptime);    TC_STATS(microuptime);
TC_STATS(bintime);      TC_STATS(nanotime);      TC_STATS(microtime);
TC_STATS(getbinuptime); TC_STATS(getnanouptime); TC_STATS(getmicrouptime);
TC_STATS(getbintime);   TC_STATS(getnanotime);   TC_STATS(getmicrotime);
TC_STATS(setclock);
#define TC_COUNT(var)   var.ev_count++
#undef TC_STATS
#else
#define TC_COUNT(var)   /* nothing */
#endif  /* TC_COUNTERS */

static void tc_windup(void);

/*
 * Return the difference between the timehands' counter value now and what
 * was when we copied it to the timehands' offset_count.
 */
static inline u_int
tc_delta(struct timehands *th)
{
        struct timecounter *tc;

        tc = th->th_counter;
        return (tc->tc_get_timecount(tc) -
                 th->th_offset_count) & tc->tc_counter_mask;
}

/*
 * Functions for reading the time.  We have to loop until we are sure that
 * the timehands that we operated on was not updated under our feet.  See
 * the comment in <sys/timevar.h> for a description of these 12 functions.
 */

void
binuptime(struct bintime *bt)
{
        struct timehands *th;
        lwp_t *l;
        u_int lgen, gen;

        TC_COUNT(nbinuptime);

        /*
         * Provide exclusion against tc_detach().
         *
         * We record the number of timecounter removals before accessing
         * timecounter state.  Note that the LWP can be using multiple
         * "generations" at once, due to interrupts (interrupted while in
         * this function).  Hardware interrupts will borrow the interrupted
         * LWP's l_tcgen value for this purpose, and can themselves be
         * interrupted by higher priority interrupts.  In this case we need
         * to ensure that the oldest generation in use is recorded.
         *
         * splsched() is too expensive to use, so we take care to structure
         * this code in such a way that it is not required.  Likewise, we
         * do not disable preemption.
         *
         * Memory barriers are also too expensive to use for such a
         * performance critical function.  The good news is that we do not
         * need memory barriers for this type of exclusion, as the thread
         * updating timecounter_removals will issue a broadcast cross call
         * before inspecting our l_tcgen value (this elides memory ordering
         * issues).
         *
         * XXX If the author of the above comment knows how to make it
         * safe to avoid memory barriers around the access to
         * th->th_generation, I'm all ears.
         */
        l = curlwp;
        lgen = l->l_tcgen;
        if (__predict_true(lgen == 0)) {
                l->l_tcgen = timecounter_removals;
        }
        __insn_barrier();

        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                *bt = th->th_offset;
                bintime_addx(bt, th->th_scale * tc_delta(th));
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);

        __insn_barrier();
        l->l_tcgen = lgen;
}

void
nanouptime(struct timespec *tsp)
{
        struct bintime bt;

        TC_COUNT(nnanouptime);
        binuptime(&bt);
        bintime2timespec(&bt, tsp);
}

void
microuptime(struct timeval *tvp)
{
        struct bintime bt;

        TC_COUNT(nmicrouptime);
        binuptime(&bt);
        bintime2timeval(&bt, tvp);
}

void
bintime(struct bintime *bt)
{
        struct bintime boottime;

        TC_COUNT(nbintime);
        binuptime(bt);
        getbinboottime(&boottime);
        bintime_add(bt, &boottime);
}

void
nanotime(struct timespec *tsp)
{
        struct bintime bt;

        TC_COUNT(nnanotime);
        bintime(&bt);
        bintime2timespec(&bt, tsp);
}

void
microtime(struct timeval *tvp)
{
        struct bintime bt;

        TC_COUNT(nmicrotime);
        bintime(&bt);
        bintime2timeval(&bt, tvp);
}

void
getbinuptime(struct bintime *bt)
{
        struct timehands *th;
        u_int gen;

        TC_COUNT(ngetbinuptime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                *bt = th->th_offset;
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
}

void
getnanouptime(struct timespec *tsp)
{
        struct timehands *th;
        u_int gen;

        TC_COUNT(ngetnanouptime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                bintime2timespec(&th->th_offset, tsp);
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
}

void
getmicrouptime(struct timeval *tvp)
{
        struct timehands *th;
        u_int gen;

        TC_COUNT(ngetmicrouptime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                bintime2timeval(&th->th_offset, tvp);
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
}

void
getbintime(struct bintime *bt)
{
        struct timehands *th;
        struct bintime boottime;
        u_int gen;

        TC_COUNT(ngetbintime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                *bt = th->th_offset;
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
        getbinboottime(&boottime);
        bintime_add(bt, &boottime);
}

static inline void
dogetnanotime(struct timespec *tsp)
{
        struct timehands *th;
        u_int gen;

        TC_COUNT(ngetnanotime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                *tsp = th->th_nanotime;
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
}

void
getnanotime(struct timespec *tsp)
{

        dogetnanotime(tsp);
}

void dtrace_getnanotime(struct timespec *tsp);

void
dtrace_getnanotime(struct timespec *tsp)
{

        dogetnanotime(tsp);
}

void
getmicrotime(struct timeval *tvp)
{
        struct timehands *th;
        u_int gen;

        TC_COUNT(ngetmicrotime);
        do {
                th = atomic_load_consume(&timehands);
                gen = th->th_generation;
                membar_consumer();
                *tvp = th->th_microtime;
                membar_consumer();
        } while (gen == 0 || gen != th->th_generation);
}

void
getnanoboottime(struct timespec *tsp)
{
        struct bintime bt;

        getbinboottime(&bt);
        bintime2timespec(&bt, tsp);
}

void
getmicroboottime(struct timeval *tvp)
{
        struct bintime bt;

        getbinboottime(&bt);
        bintime2timeval(&bt, tvp);
}

void
getbinboottime(struct bintime *basep)
{
        struct bintime base;
        unsigned gen;

        do {
                /* Spin until the timebase isn't changing.  */
                while ((gen = atomic_load_relaxed(&timebase.gen)) & 1)
                        SPINLOCK_BACKOFF_HOOK;

                /* Read out a snapshot of the timebase.  */
                membar_consumer();
                base = timebase.bin;
                membar_consumer();

                /* Restart if it changed while we were reading.  */
        } while (gen != atomic_load_relaxed(&timebase.gen));

        *basep = base;
}

/*
 * Initialize a new timecounter and possibly use it.
 */
void
tc_init(struct timecounter *tc)
{
        u_int u;

        KASSERTMSG(tc->tc_next == NULL, "timecounter %s already initialised",
            tc->tc_name);

        u = tc->tc_frequency / tc->tc_counter_mask;
        /* XXX: We need some margin here, 10% is a guess */
        u *= 11;
        u /= 10;
        if (u > hz && tc->tc_quality >= 0) {
                tc->tc_quality = -2000;
                aprint_verbose(
                    "timecounter: Timecounter \"%s\" frequency %ju Hz",
                            tc->tc_name, (uintmax_t)tc->tc_frequency);
                aprint_verbose(" -- Insufficient hz, needs at least %u\n", u);
        } else if (tc->tc_quality >= 0 || bootverbose) {
                aprint_verbose(
                    "timecounter: Timecounter \"%s\" frequency %ju Hz "
                    "quality %d\n", tc->tc_name, (uintmax_t)tc->tc_frequency,
                    tc->tc_quality);
        }

        mutex_spin_enter(&timecounter_lock);
        tc->tc_next = timecounters;
        timecounters = tc;
        timecounter_mods++;
        /*
         * Never automatically use a timecounter with negative quality.
         * Even though we run on the dummy counter, switching here may be
         * worse since this timecounter may not be monotonous.
         */
        if (tc->tc_quality >= 0 && (tc->tc_quality > timecounter->tc_quality ||
            (tc->tc_quality == timecounter->tc_quality &&
            tc->tc_frequency > timecounter->tc_frequency))) {
                (void)tc->tc_get_timecount(tc);
                (void)tc->tc_get_timecount(tc);
                timecounter = tc;
                tc_windup();
        }
        mutex_spin_exit(&timecounter_lock);
}

/*
 * Pick a new timecounter due to the existing counter going bad.
 */
static void
tc_pick(void)
{
        struct timecounter *best, *tc;

        KASSERT(mutex_owned(&timecounter_lock));

        for (best = tc = timecounters; tc != NULL; tc = tc->tc_next) {
                if (tc->tc_quality > best->tc_quality)
                        best = tc;
                else if (tc->tc_quality < best->tc_quality)
                        continue;
                else if (tc->tc_frequency > best->tc_frequency)
                        best = tc;
        }
        (void)best->tc_get_timecount(best);
        (void)best->tc_get_timecount(best);
        timecounter = best;
}

/*
 * A timecounter has gone bad, arrange to pick a new one at the next
 * clock tick.
 */
void
tc_gonebad(struct timecounter *tc)
{

        tc->tc_quality = -100;
        membar_producer();
        atomic_inc_uint(&timecounter_bad);
}

/*
 * Stop using a timecounter and remove it from the timecounters list.
 */
int
tc_detach(struct timecounter *target)
{
        struct timecounter *tc;
        struct timecounter **tcp = NULL;
        int removals;
        lwp_t *l;

        /* First, find the timecounter. */
        mutex_spin_enter(&timecounter_lock);
        for (tcp = &timecounters, tc = timecounters;
             tc != NULL;
             tcp = &tc->tc_next, tc = tc->tc_next) {
                if (tc == target)
                        break;
        }
        if (tc == NULL) {
                mutex_spin_exit(&timecounter_lock);
                return SET_ERROR(ESRCH);
        }

        /* And now, remove it. */
        *tcp = tc->tc_next;
        if (timecounter == target) {
                tc_pick();
                tc_windup();
        }
        timecounter_mods++;
        removals = timecounter_removals++;
        mutex_spin_exit(&timecounter_lock);

        /*
         * We now have to determine if any threads in the system are still
         * making use of this timecounter.
         *
         * We issue a broadcast cross call to elide memory ordering issues,
         * then scan all LWPs in the system looking at each's timecounter
         * generation number.  We need to see a value of zero (not actively
         * using a timecounter) or a value greater than our removal value.
         *
         * We may race with threads that read `timecounter_removals' and
         * and then get preempted before updating `l_tcgen'.  This is not
         * a problem, since it means that these threads have not yet started
         * accessing timecounter state.  All we do need is one clean
         * snapshot of the system where every thread appears not to be using
         * old timecounter state.
         */
        for (;;) {
                xc_barrier(0);

                mutex_enter(&proc_lock);
                LIST_FOREACH(l, &alllwp, l_list) {
                        if (l->l_tcgen == 0 || l->l_tcgen > removals) {
                                /*
                                 * Not using timecounter or old timecounter
                                 * state at time of our xcall or later.
                                 */
                                continue;
                        }
                        break;
                }
                mutex_exit(&proc_lock);

                /*
                 * If the timecounter is still in use, wait at least 10ms
                 * before retrying.
                 */
                if (l == NULL) {
                        break;
                }
                (void)kpause("tcdetach", false, mstohz(10), NULL);
        }

        tc->tc_next = NULL;
        return 0;
}

/* Report the frequency of the current timecounter. */
uint64_t
tc_getfrequency(void)
{

        return atomic_load_consume(&timehands)->th_counter->tc_frequency;
}

/*
 * Step our concept of UTC.  This is done by modifying our estimate of
 * when we booted.
 */
void
tc_setclock(const struct timespec *ts)
{
        struct timespec ts2;
        struct bintime bt, bt2;

        mutex_spin_enter(&timecounter_lock);
        TC_COUNT(nsetclock);
        binuptime(&bt2);
        timespec2bintime(ts, &bt);
        bintime_sub(&bt, &bt2);
        bintime_add(&bt2, &timebase.bin);
        timebase.gen |= 1;      /* change in progress */
        membar_producer();
        timebase.bin = bt;
        membar_producer();
        timebase.gen++;         /* commit change */
        tc_windup();
        mutex_spin_exit(&timecounter_lock);

        if (timestepwarnings) {
                bintime2timespec(&bt2, &ts2);
                log(LOG_INFO,
                    "Time stepped from %lld.%09ld to %lld.%09ld\n",
                    (long long)ts2.tv_sec, ts2.tv_nsec,
                    (long long)ts->tv_sec, ts->tv_nsec);
        }
}

/*
 * Initialize the next struct timehands in the ring and make
 * it the active timehands.  Along the way we might switch to a different
 * timecounter and/or do seconds processing in NTP.  Slightly magic.
 */
static void
tc_windup(void)
{
        struct bintime bt;
        struct timehands *th, *tho;
        uint64_t scale;
        u_int delta, ncount, ogen;
        int i, s_update;
        time_t t;

        KASSERT(mutex_owned(&timecounter_lock));

        s_update = 0;

        /*
         * Make the next timehands a copy of the current one, but do not
         * overwrite the generation or next pointer.  While we update
         * the contents, the generation must be zero.  Ensure global
         * visibility of the generation before proceeding.
         */
        tho = timehands;
        th = tho->th_next;
        ogen = th->th_generation;
        th->th_generation = 0;
        membar_producer();
        bcopy(tho, th, offsetof(struct timehands, th_generation));

        /*
         * Capture a timecounter delta on the current timecounter and if
         * changing timecounters, a counter value from the new timecounter.
         * Update the offset fields accordingly.
         */
        delta = tc_delta(th);
        if (th->th_counter != timecounter)
                ncount = timecounter->tc_get_timecount(timecounter);
        else
                ncount = 0;
        th->th_offset_count += delta;
        bintime_addx(&th->th_offset, th->th_scale * delta);

        /*
         * Hardware latching timecounters may not generate interrupts on
         * PPS events, so instead we poll them.  There is a finite risk that
         * the hardware might capture a count which is later than the one we
         * got above, and therefore possibly in the next NTP second which might
         * have a different rate than the current NTP second.  It doesn't
         * matter in practice.
         */
        if (tho->th_counter->tc_poll_pps)
                tho->th_counter->tc_poll_pps(tho->th_counter);

        /*
         * Deal with NTP second processing.  The for loop normally
         * iterates at most once, but in extreme situations it might
         * keep NTP sane if timeouts are not run for several seconds.
         * At boot, the time step can be large when the TOD hardware
         * has been read, so on really large steps, we call
         * ntp_update_second only twice.  We need to call it twice in
         * case we missed a leap second.
         * If NTP is not compiled in ntp_update_second still calculates
         * the adjustment resulting from adjtime() calls.
         */
        bt = th->th_offset;
        bintime_add(&bt, &timebase.bin);
        i = bt.sec - tho->th_microtime.tv_sec;
        if (i > LARGE_STEP)
                i = 2;
        for (; i > 0; i--) {
                t = bt.sec;
                ntp_update_second(&th->th_adjustment, &bt.sec);
                s_update = 1;
                if (bt.sec != t) {
                        timebase.gen |= 1;      /* change in progress */
                        membar_producer();
                        timebase.bin.sec += bt.sec - t;
                        membar_producer();
                        timebase.gen++;         /* commit change */
                }
        }

        /* Update the UTC timestamps used by the get*() functions. */
        /* XXX shouldn't do this here.  Should force non-`get' versions. */
        bintime2timeval(&bt, &th->th_microtime);
        bintime2timespec(&bt, &th->th_nanotime);
        /* Now is a good time to change timecounters. */
        if (th->th_counter != timecounter) {
                th->th_counter = timecounter;
                th->th_offset_count = ncount;
                s_update = 1;
        }

        /*-
         * Recalculate the scaling factor.  We want the number of 1/2^64
         * fractions of a second per period of the hardware counter, taking
         * into account the th_adjustment factor which the NTP PLL/adjtime(2)
         * processing provides us with.
         *
         * The th_adjustment is nanoseconds per second with 32 bit binary
         * fraction and we want 64 bit binary fraction of second:
         *
         *       x = a * 2^32 / 10^9 = a * 4.294967296
         *
         * The range of th_adjustment is +/- 5000PPM so inside a 64bit int
         * we can only multiply by about 850 without overflowing, but that
         * leaves suitably precise fractions for multiply before divide.
         *
         * Divide before multiply with a fraction of 2199/512 results in a
         * systematic undercompensation of 10PPM of th_adjustment.  On a
         * 5000PPM adjustment this is a 0.05PPM error.  This is acceptable.
         *
         * We happily sacrifice the lowest of the 64 bits of our result
         * to the goddess of code clarity.
         *
         */
        if (s_update) {
                scale = (uint64_t)1 << 63;
                scale += (th->th_adjustment / 1024) * 2199;
                scale /= th->th_counter->tc_frequency;
                th->th_scale = scale * 2;
        }
        /*
         * Now that the struct timehands is again consistent, set the new
         * generation number, making sure to not make it zero.  Ensure
         * changes are globally visible before changing.
         */
        if (++ogen == 0)
                ogen = 1;
        membar_producer();
        th->th_generation = ogen;

        /*
         * Go live with the new struct timehands.  Ensure changes are
         * globally visible before changing.
         */
        setrealuptime(th->th_microtime.tv_sec, th->th_offset.sec);
        atomic_store_release(&timehands, th);

        /*
         * Force users of the old timehand to move on.  This is
         * necessary for MP systems; we need to ensure that the
         * consumers will move away from the old timehand before
         * we begin updating it again when we eventually wrap
         * around.
         */
        if (++tho->th_generation == 0)
                tho->th_generation = 1;
}

/*
 * RFC 2783 PPS-API implementation.
 */

int
pps_ioctl(u_long cmd, void *data, struct pps_state *pps)
{
        pps_params_t *app;
        pps_info_t *pipi;
#ifdef PPS_SYNC
        int *epi;
#endif

        KASSERT(mutex_owned(&timecounter_lock));

        KASSERT(pps != NULL);

        switch (cmd) {
        case PPS_IOC_CREATE:
                return 0;
        case PPS_IOC_DESTROY:
                return 0;
        case PPS_IOC_SETPARAMS:
                app = (pps_params_t *)data;
                if (app->mode & ~pps->ppscap)
                        return SET_ERROR(EINVAL);
                pps->ppsparam = *app;
                return 0;
        case PPS_IOC_GETPARAMS:
                app = (pps_params_t *)data;
                *app = pps->ppsparam;
                app->api_version = PPS_API_VERS_1;
                return 0;
        case PPS_IOC_GETCAP:
                *(int*)data = pps->ppscap;
                return 0;
        case PPS_IOC_FETCH:
                pipi = (pps_info_t *)data;
                pps->ppsinfo.current_mode = pps->ppsparam.mode;
                *pipi = pps->ppsinfo;
                return 0;
        case PPS_IOC_KCBIND:
#ifdef PPS_SYNC
                epi = (int *)data;
                /* XXX Only root should be able to do this */
                if (*epi & ~pps->ppscap)
                        return SET_ERROR(EINVAL);
                pps->kcmode = *epi;
                return 0;
#else
                return SET_ERROR(EOPNOTSUPP);
#endif
        default:
                return SET_ERROR(EPASSTHROUGH);
        }
}

void
pps_init(struct pps_state *pps)
{

        KASSERT(mutex_owned(&timecounter_lock));

        pps->ppscap |= PPS_TSFMT_TSPEC;
        if (pps->ppscap & PPS_CAPTUREASSERT)
                pps->ppscap |= PPS_OFFSETASSERT;
        if (pps->ppscap & PPS_CAPTURECLEAR)
                pps->ppscap |= PPS_OFFSETCLEAR;
}

/*
 * capture a timestamp in the pps structure
 */
void
pps_capture(struct pps_state *pps)
{
        struct timehands *th;

        KASSERT(mutex_owned(&timecounter_lock));
        KASSERT(pps != NULL);

        th = timehands;
        pps->capgen = th->th_generation;
        pps->capth = th;
        pps->capcount = (uint64_t)tc_delta(th) + th->th_offset_count;
        if (pps->capgen != th->th_generation)
                pps->capgen = 0;
}

#ifdef PPS_DEBUG
int ppsdebug = 0;
#endif

/*
 * process a pps_capture()ed event
 */
void
pps_event(struct pps_state *pps, int event)
{
        pps_ref_event(pps, event, NULL, PPS_REFEVNT_PPS|PPS_REFEVNT_CAPTURE);
}

/*
 * extended pps api /  kernel pll/fll entry point
 *
 * feed reference time stamps to PPS engine
 *
 * will simulate a PPS event and feed
 * the NTP PLL/FLL if requested.
 *
 * the ref time stamps should be roughly once
 * a second but do not need to be exactly in phase
 * with the UTC second but should be close to it.
 * this relaxation of requirements allows callout
 * driven timestamping mechanisms to feed to pps
 * capture/kernel pll logic.
 *
 * calling pattern is:
 *  pps_capture() (for PPS_REFEVNT_{CAPTURE|CAPCUR})
 *  read timestamp from reference source
 *  pps_ref_event()
 *
 * supported refmodes:
 *  PPS_REFEVNT_CAPTURE
 *    use system timestamp of pps_capture()
 *  PPS_REFEVNT_CURRENT
 *    use system timestamp of this call
 *  PPS_REFEVNT_CAPCUR
 *    use average of read capture and current system time stamp
 *  PPS_REFEVNT_PPS
 *    assume timestamp on second mark - ref_ts is ignored
 *
 */

void
pps_ref_event(struct pps_state *pps,
              int event,
              struct bintime *ref_ts,
              int refmode
        )
{
        struct bintime bt;      /* current time */
        struct bintime btd;     /* time difference */
        struct bintime bt_ref;  /* reference time */
        struct timespec ts, *tsp, *osp;
        struct timehands *th;
        uint64_t tcount, acount, dcount, *pcount;
        int foff, gen;
#ifdef PPS_SYNC
        int fhard;
#endif
        pps_seq_t *pseq;

        KASSERT(mutex_owned(&timecounter_lock));

        KASSERT(pps != NULL);

        /* pick up current time stamp if needed */
        if (refmode & (PPS_REFEVNT_CURRENT|PPS_REFEVNT_CAPCUR)) {
                /* pick up current time stamp */
                th = timehands;
                gen = th->th_generation;
                tcount = (uint64_t)tc_delta(th) + th->th_offset_count;
                if (gen != th->th_generation)
                        gen = 0;

                /* If the timecounter was wound up underneath us, bail out. */
                if (pps->capgen == 0 ||
                    pps->capgen != pps->capth->th_generation ||
                    gen == 0 ||
                    gen != pps->capgen) {
#ifdef PPS_DEBUG
                        if (ppsdebug & 0x1) {
                                log(LOG_DEBUG,
                                    "pps_ref_event(pps=%p, event=%d, ...): DROP (wind-up)\n",
                                    pps, event);
                        }
#endif
                        return;
                }
        } else {
                tcount = 0;     /* keep GCC happy */
        }

#ifdef PPS_DEBUG
        if (ppsdebug & 0x1) {
                struct timespec tmsp;

                if (ref_ts == NULL) {
                        tmsp.tv_sec = 0;
                        tmsp.tv_nsec = 0;
                } else {
                        bintime2timespec(ref_ts, &tmsp);
                }

                log(LOG_DEBUG,
                    "pps_ref_event(pps=%p, event=%d, ref_ts=%"PRIi64
                    ".%09"PRIi32", refmode=0x%1x)\n",
                    pps, event, tmsp.tv_sec, (int32_t)tmsp.tv_nsec, refmode);
        }
#endif

        /* setup correct event references */
        if (event == PPS_CAPTUREASSERT) {
                tsp = &pps->ppsinfo.assert_timestamp;
                osp = &pps->ppsparam.assert_offset;
                foff = pps->ppsparam.mode & PPS_OFFSETASSERT;
#ifdef PPS_SYNC
                fhard = pps->kcmode & PPS_CAPTUREASSERT;
#endif
                pcount = &pps->ppscount[0];
                pseq = &pps->ppsinfo.assert_sequence;
        } else {
                tsp = &pps->ppsinfo.clear_timestamp;
                osp = &pps->ppsparam.clear_offset;
                foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
#ifdef PPS_SYNC
                fhard = pps->kcmode & PPS_CAPTURECLEAR;
#endif
                pcount = &pps->ppscount[1];
                pseq = &pps->ppsinfo.clear_sequence;
        }

        /* determine system time stamp according to refmode */
        dcount = 0;             /* keep GCC happy */
        switch (refmode & PPS_REFEVNT_RMASK) {
        case PPS_REFEVNT_CAPTURE:
                acount = pps->capcount; /* use capture timestamp */
                break;

        case PPS_REFEVNT_CURRENT:
                acount = tcount; /* use current timestamp */
                break;

        case PPS_REFEVNT_CAPCUR:
                /*
                 * calculate counter value between pps_capture() and
                 * pps_ref_event()
                 */
                dcount = tcount - pps->capcount;
                acount = (dcount / 2) + pps->capcount;
                break;

        default:                /* ignore call error silently */
                return;
        }

        /*
         * If the timecounter changed, we cannot compare the count values, so
         * we have to drop the rest of the PPS-stuff until the next event.
         */
        if (pps->ppstc != pps->capth->th_counter) {
                pps->ppstc = pps->capth->th_counter;
                pps->capcount = acount;
                *pcount = acount;
                pps->ppscount[2] = acount;
#ifdef PPS_DEBUG
                if (ppsdebug & 0x1) {
                        log(LOG_DEBUG,
                            "pps_ref_event(pps=%p, event=%d, ...): DROP (time-counter change)\n",
                            pps, event);
                }
#endif
                return;
        }

        pps->capcount = acount;

        /* Convert the count to a bintime. */
        bt = pps->capth->th_offset;
        bintime_addx(&bt, pps->capth->th_scale * (acount - pps->capth->th_offset_count));
        bintime_add(&bt, &timebase.bin);

        if ((refmode & PPS_REFEVNT_PPS) == 0) {
                /* determine difference to reference time stamp */
                bt_ref = *ref_ts;

                btd = bt;
                bintime_sub(&btd, &bt_ref);

                /*
                 * simulate a PPS timestamp by dropping the fraction
                 * and applying the offset
                 */
                if (bt.frac >= (uint64_t)1<<63) /* skip to nearest second */
                        bt.sec++;
                bt.frac = 0;
                bintime_add(&bt, &btd);
        } else {
                /*
                 * create ref_ts from current time -
                 * we are supposed to be called on
                 * the second mark
                 */
                bt_ref = bt;
                if (bt_ref.frac >= (uint64_t)1<<63)     /* skip to nearest second */
                        bt_ref.sec++;
                bt_ref.frac = 0;
        }

        /* convert bintime to timestamp */
        bintime2timespec(&bt, &ts);

        /* If the timecounter was wound up underneath us, bail out. */
        if (pps->capgen != pps->capth->th_generation)
                return;

        /* store time stamp */
        *pcount = pps->capcount;
        (*pseq)++;
        *tsp = ts;

        /* add offset correction */
        if (foff) {
                timespecadd(tsp, osp, tsp);
                if (tsp->tv_nsec < 0) {
                        tsp->tv_nsec += 1000000000;
                        tsp->tv_sec -= 1;
                }
        }

#ifdef PPS_DEBUG
        if (ppsdebug & 0x2) {
                struct timespec ts2;
                struct timespec ts3;

                bintime2timespec(&bt_ref, &ts2);

                bt.sec = 0;
                bt.frac = 0;

                if (refmode & PPS_REFEVNT_CAPCUR) {
                            bintime_addx(&bt, pps->capth->th_scale * dcount);
                }
                bintime2timespec(&bt, &ts3);

                log(LOG_DEBUG, "ref_ts=%"PRIi64".%09"PRIi32
                    ", ts=%"PRIi64".%09"PRIi32", read latency=%"PRIi64" ns\n",
                    ts2.tv_sec, (int32_t)ts2.tv_nsec,
                    tsp->tv_sec, (int32_t)tsp->tv_nsec,
                    timespec2ns(&ts3));
        }
#endif

#ifdef PPS_SYNC
        if (fhard) {
                uint64_t scale;
                uint64_t div;

                /*
                 * Feed the NTP PLL/FLL.
                 * The FLL wants to know how many (hardware) nanoseconds
                 * elapsed since the previous event (mod 1 second) thus
                 * we are actually looking at the frequency difference scaled
                 * in nsec.
                 * As the counter time stamps are not truly at 1Hz
                 * we need to scale the count by the elapsed
                 * reference time.
                 * valid sampling interval: [0.5..2[ sec
                 */

                /* calculate elapsed raw count */
                tcount = pps->capcount - pps->ppscount[2];
                pps->ppscount[2] = pps->capcount;
                tcount &= pps->capth->th_counter->tc_counter_mask;

                /* calculate elapsed ref time */
                btd = bt_ref;
                bintime_sub(&btd, &pps->ref_time);
                pps->ref_time = bt_ref;

                /* check that we stay below 2 sec */
                if (btd.sec < 0 || btd.sec > 1)
                        return;

                /* we want at least 0.5 sec between samples */
                if (btd.sec == 0 && btd.frac < (uint64_t)1<<63)
                        return;

                /*
                 * calculate cycles per period by multiplying
                 * the frequency with the elapsed period
                 * we pick a fraction of 30 bits
                 * ~1ns resolution for elapsed time
                 */
                div   = (uint64_t)btd.sec << 30;
                div  |= (btd.frac >> 34) & (((uint64_t)1 << 30) - 1);
                div  *= pps->capth->th_counter->tc_frequency;
                div >>= 30;

                if (div == 0)   /* safeguard */
                        return;

                scale = (uint64_t)1 << 63;
                scale /= div;
                scale *= 2;

                bt.sec = 0;
                bt.frac = 0;
                bintime_addx(&bt, scale * tcount);
                bintime2timespec(&bt, &ts);

#ifdef PPS_DEBUG
                if (ppsdebug & 0x4) {
                        struct timespec ts2;
                        int64_t df;

                        bintime2timespec(&bt_ref, &ts2);
                        df = timespec2ns(&ts);
                        if (df > 500000000)
                                df -= 1000000000;
                        log(LOG_DEBUG, "hardpps: ref_ts=%"PRIi64
                            ".%09"PRIi32", ts=%"PRIi64".%09"PRIi32
                            ", freqdiff=%"PRIi64" ns/s\n",
                            ts2.tv_sec, (int32_t)ts2.tv_nsec,
                            tsp->tv_sec, (int32_t)tsp->tv_nsec,
                            df);
                }
#endif

                hardpps(tsp, timespec2ns(&ts));
        }
#endif
}

/*
 * Timecounters need to be updated every so often to prevent the hardware
 * counter from overflowing.  Updating also recalculates the cached values
 * used by the get*() family of functions, so their precision depends on
 * the update frequency.
 */

static int tc_tick;

void
tc_ticktock(void)
{
        static int count;

        if (++count < tc_tick)
                return;
        count = 0;
        mutex_spin_enter(&timecounter_lock);
        if (__predict_false(timecounter_bad != 0)) {
                /* An existing timecounter has gone bad, pick a new one. */
                (void)atomic_swap_uint(&timecounter_bad, 0);
                if (timecounter->tc_quality < 0) {
                        tc_pick();
                }
        }
        tc_windup();
        mutex_spin_exit(&timecounter_lock);
}

void
inittimecounter(void)
{
        u_int p;

        mutex_init(&timecounter_lock, MUTEX_DEFAULT, IPL_HIGH);

        /*
         * Set the initial timeout to
         * max(1, <approx. number of hardclock ticks in a millisecond>).
         * People should probably not use the sysctl to set the timeout
         * to smaller than its initial value, since that value is the
         * smallest reasonable one.  If they want better timestamps they
         * should use the non-"get"* functions.
         */
        if (hz > 1000)
                tc_tick = (hz + 500) / 1000;
        else
                tc_tick = 1;
        p = (tc_tick * 1000000) / hz;
        aprint_verbose("timecounter: Timecounters tick every %d.%03u msec\n",
            p / 1000, p % 1000);

        /* warm up new timecounter (again) and get rolling. */
        (void)timecounter->tc_get_timecount(timecounter);
        (void)timecounter->tc_get_timecount(timecounter);
}