/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * Copyright (c) 2008-2021 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz and Don Ahn.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      from: @(#)clock.c       7.2 (Berkeley) 5/12/91
 * $FreeBSD: src/sys/i386/isa/clock.c,v 1.149.2.6 2002/11/02 04:41:50 iwasaki Exp $
 */

/*
 * Routines to handle clock hardware.
 */

/*
 * inittodr, settodr and support routines written
 * by Christoph Robitschko <chmr@edvz.tu-graz.ac.at>
 *
 * reintroduced and updated by Chris Stenton <chris@gnome.co.uk> 8/10/94
 */

#if 0
#include "opt_clock.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/eventhandler.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/sysctl.h>
#include <sys/cons.h>
#include <sys/kbio.h>
#include <sys/systimer.h>
#include <sys/globaldata.h>
#include <sys/machintr.h>
#include <sys/interrupt.h>

#include <sys/thread2.h>

#include <machine/clock.h>
#include <machine/cputypes.h>
#include <machine/frame.h>
#include <machine/ipl.h>
#include <machine/limits.h>
#include <machine/md_var.h>
#include <machine/psl.h>
#include <machine/segments.h>
#include <machine/smp.h>
#include <machine/specialreg.h>
#include <machine/intr_machdep.h>

#include <machine_base/apic/ioapic.h>
#include <machine_base/apic/ioapic_abi.h>
#include <machine_base/icu/icu.h>
#include <bus/isa/isa.h>
#include <bus/isa/rtc.h>
#include <machine_base/isa/timerreg.h>

SET_DECLARE(timecounter_init_set, const timecounter_init_t);
TIMECOUNTER_INIT(placeholder, NULL);

static void i8254_restore(void);
static void resettodr_on_shutdown(void *arg __unused);

/*
 * 32-bit time_t's can't reach leap years before 1904 or after 2036, so we
 * can use a simple formula for leap years.
 */
#define LEAPYEAR(y) ((u_int)(y) % 4 == 0)
#define DAYSPERYEAR   (31+28+31+30+31+30+31+31+30+31+30+31)

#ifndef TIMER_FREQ
#define TIMER_FREQ   1193182
#endif

static uint8_t i8254_walltimer_sel;
static uint16_t i8254_walltimer_cntr;
static int timer0_running;

int     adjkerntz;              /* local offset from GMT in seconds */
int     disable_rtc_set;        /* disable resettodr() if != 0 */
int     tsc_present;
int     tsc_invariant;
int     tsc_mpsync;
int     wall_cmos_clock;        /* wall CMOS clock assumed if != 0 */
tsc_uclock_t tsc_frequency;
tsc_uclock_t tsc_oneus_approx;  /* always at least 1, approx only */

enum tstate { RELEASED, ACQUIRED };
static enum tstate timer0_state;
static enum tstate timer1_state;
static enum tstate timer2_state;

int     i8254_cputimer_disable; /* No need to initialize i8254 cputimer. */

static  int     beeping = 0;
static  const u_char daysinmonth[] = {31,28,31,30,31,30,31,31,30,31,30,31};
static  u_char  rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
static  u_char  rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
static  int     rtc_loaded;

static  sysclock_t i8254_cputimer_div;

static int i8254_nointr;
static int i8254_intr_disable = 1;
TUNABLE_INT("hw.i8254.intr_disable", &i8254_intr_disable);

static int calibrate_timers_with_rtc = 0;
TUNABLE_INT("hw.calibrate_timers_with_rtc", &calibrate_timers_with_rtc);

static int calibrate_tsc_fast = 1;
TUNABLE_INT("hw.calibrate_tsc_fast", &calibrate_tsc_fast);

static int calibrate_test;
TUNABLE_INT("hw.tsc_calibrate_test", &calibrate_test);

static struct callout sysbeepstop_ch;

static sysclock_t i8254_cputimer_count(void);
static void i8254_cputimer_construct(struct cputimer *cputimer, sysclock_t last);
static void i8254_cputimer_destruct(struct cputimer *cputimer);

static struct cputimer  i8254_cputimer = {
    .next               = SLIST_ENTRY_INITIALIZER,
    .name               = "i8254",
    .pri                = CPUTIMER_PRI_8254,
    .type               = 0,    /* determined later */
    .count              = i8254_cputimer_count,
    .fromhz             = cputimer_default_fromhz,
    .fromus             = cputimer_default_fromus,
    .construct          = i8254_cputimer_construct,
    .destruct           = i8254_cputimer_destruct,
    .freq               = TIMER_FREQ
};

static void i8254_intr_reload(struct cputimer_intr *, sysclock_t);
static void i8254_intr_config(struct cputimer_intr *, const struct cputimer *);
static void i8254_intr_initclock(struct cputimer_intr *, boolean_t);

static struct cputimer_intr i8254_cputimer_intr = {
    .freq = TIMER_FREQ,
    .reload = i8254_intr_reload,
    .enable = cputimer_intr_default_enable,
    .config = i8254_intr_config,
    .restart = cputimer_intr_default_restart,
    .pmfixup = cputimer_intr_default_pmfixup,
    .initclock = i8254_intr_initclock,
    .pcpuhand = NULL,
    .next = SLIST_ENTRY_INITIALIZER,
    .name = "i8254",
    .type = CPUTIMER_INTR_8254,
    .prio = CPUTIMER_INTR_PRIO_8254,
    .caps = CPUTIMER_INTR_CAP_PS,
    .priv = NULL
};

/*
 * Use this to lwkt_switch() when the scheduler clock is not
 * yet running, otherwise lwkt_switch() won't do anything.
 * XXX needs cleaning up in lwkt_thread.c
 */
static void
lwkt_force_switch(void)
{
        crit_enter();
        lwkt_schedulerclock(curthread);
        crit_exit();
        lwkt_switch();
}

/*
 * timer0 clock interrupt.  Timer0 is in one-shot mode and has stopped
 * counting as of this interrupt.  We use timer1 in free-running mode (not
 * generating any interrupts) as our main counter.  Each cpu has timeouts
 * pending.
 *
 * This code is INTR_MPSAFE and may be called without the BGL held.
 */
static void
clkintr(void *dummy, void *frame_arg)
{
        static sysclock_t sysclock_count;       /* NOTE! Must be static */
        struct globaldata *gd = mycpu;
        struct globaldata *gscan;
        int n;

        /*
         * SWSTROBE mode is a one-shot, the timer is no longer running
         */
        timer0_running = 0;

        /*
         * XXX the dispatcher needs work.  right now we call systimer_intr()
         * directly or via IPI for any cpu with systimers queued, which is
         * usually *ALL* of them.  We need to use the LAPIC timer for this.
         */
        sysclock_count = sys_cputimer->count();
        for (n = 0; n < ncpus; ++n) {
            gscan = globaldata_find(n);
            if (TAILQ_FIRST(&gscan->gd_systimerq) == NULL)
                continue;
            if (gscan != gd) {
                lwkt_send_ipiq3(gscan, (ipifunc3_t)systimer_intr,
                                &sysclock_count, 1);
            } else {
                systimer_intr(&sysclock_count, 0, frame_arg);
            }
        }
}


/*
 * NOTE! not MP safe.
 */
int
acquire_timer2(int mode)
{
        if (timer2_state != RELEASED)
                return (-1);
        timer2_state = ACQUIRED;

        /*
         * This access to the timer registers is as atomic as possible
         * because it is a single instruction.  We could do better if we
         * knew the rate.
         */
        outb(TIMER_MODE, TIMER_SEL2 | (mode & 0x3f));
        return (0);
}

int
release_timer2(void)
{
        if (timer2_state != ACQUIRED)
                return (-1);
        outb(TIMER_MODE, TIMER_SEL2 | TIMER_SQWAVE | TIMER_16BIT);
        timer2_state = RELEASED;
        return (0);
}

#include "opt_ddb.h"
#ifdef DDB
#include <ddb/ddb.h>

DB_SHOW_COMMAND(rtc, rtc)
{
        kprintf("%02x/%02x/%02x %02x:%02x:%02x, A = %02x, B = %02x, C = %02x\n",
               rtcin(RTC_YEAR), rtcin(RTC_MONTH), rtcin(RTC_DAY),
               rtcin(RTC_HRS), rtcin(RTC_MIN), rtcin(RTC_SEC),
               rtcin(RTC_STATUSA), rtcin(RTC_STATUSB), rtcin(RTC_INTR));
}
#endif /* DDB */

/*
 * Return the current cpu timer count.
 */
static
sysclock_t
i8254_cputimer_count(void)
{
        static uint16_t cputimer_last;
        uint16_t count;
        sysclock_t ret;

        clock_lock();
        outb(TIMER_MODE, i8254_walltimer_sel | TIMER_LATCH);
        count = (uint8_t)inb(i8254_walltimer_cntr);     /* get countdown */
        count |= ((uint8_t)inb(i8254_walltimer_cntr) << 8);
        count = -count;                                 /* -> countup */
        if (count < cputimer_last)                      /* rollover */
                i8254_cputimer.base += 0x00010000U;
        ret = i8254_cputimer.base | count;
        cputimer_last = count;
        clock_unlock();

        return(ret);
}

/*
 * This function is called whenever the system timebase changes, allowing
 * us to calculate what is needed to convert a system timebase tick
 * into an 8254 tick for the interrupt timer.  If we can convert to a
 * simple shift, multiplication, or division, we do so.  Otherwise 64
 * bit arithmetic is required every time the interrupt timer is reloaded.
 */
static void
i8254_intr_config(struct cputimer_intr *cti, const struct cputimer *timer)
{
    sysclock_t freq;
    sysclock_t div;

    /*
     * Will a simple divide do the trick?
     */
    div = (timer->freq + (cti->freq / 2)) / cti->freq;
    freq = cti->freq * div;

    if (freq >= timer->freq - 1 && freq <= timer->freq + 1)
        i8254_cputimer_div = div;
    else
        i8254_cputimer_div = 0;
}

/*
 * Reload for the next timeout.  It is possible for the reload value
 * to be 0 or negative, indicating that an immediate timer interrupt
 * is desired.  For now make the minimum 2 ticks.
 *
 * We may have to convert from the system timebase to the 8254 timebase.
 */
static void
i8254_intr_reload(struct cputimer_intr *cti, sysclock_t reload)
{
    uint16_t count;

    if ((ssysclock_t)reload < 0)
            reload = 1;
    if (i8254_cputimer_div)
        reload /= i8254_cputimer_div;
    else
        reload = muldivu64(reload, cti->freq, sys_cputimer->freq);

    if (reload < 2)
        reload = 2;             /* minimum count */
    if (reload > 0xFFFF)
        reload = 0xFFFF;        /* almost full count (0 is full count) */

    clock_lock();
    if (timer0_running) {
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);     /* count-down timer */
        count = (uint8_t)inb(TIMER_CNTR0);              /* lsb */
        count |= ((uint8_t)inb(TIMER_CNTR0) << 8);      /* msb */
        if (reload < count) {
            outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
            outb(TIMER_CNTR0, (uint8_t)reload);         /* lsb */
            outb(TIMER_CNTR0, (uint8_t)(reload >> 8));  /* msb */
        }
    } else {
        timer0_running = 1;
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
        outb(TIMER_CNTR0, (uint8_t)reload);             /* lsb */
        outb(TIMER_CNTR0, (uint8_t)(reload >> 8));      /* msb */
    }
    clock_unlock();
}

/*
 * DELAY(usec)       - Spin for the specified number of microseconds.
 * DRIVERSLEEP(usec) - Spin for the specified number of microseconds,
 *                     but do a thread switch in the loop
 *
 * Relies on timer 1 counting down from (cputimer_freq / hz)
 * Note: timer had better have been programmed before this is first used!
 */
static void
DODELAY(int n, int doswitch)
{
        ssysclock_t delta, ticks_left;
        sysclock_t prev_tick, tick;

#ifdef DELAYDEBUG
        int getit_calls = 1;
        int n1;
        static int state = 0;

        if (state == 0) {
                state = 1;
                for (n1 = 1; n1 <= 10000000; n1 *= 10)
                        DELAY(n1);
                state = 2;
        }
        if (state == 1)
                kprintf("DELAY(%d)...", n);
#endif
        /*
         * Guard against the timer being uninitialized if we are called
         * early for console i/o.
         */
        if (timer0_state == RELEASED && i8254_cputimer_disable == 0)
                i8254_restore();

        /*
         * Read the counter first, so that the rest of the setup overhead is
         * counted.  Then calculate the number of hardware timer ticks
         * required, rounding up to be sure we delay at least the requested
         * number of microseconds.
         */
        prev_tick = sys_cputimer->count();
        ticks_left = muldivu64(n, sys_cputimer->freq + 999999, 1000000);

        /*
         * Loop until done.
         */
        while (ticks_left > 0) {
                tick = sys_cputimer->count();
#ifdef DELAYDEBUG
                ++getit_calls;
#endif
                delta = tick - prev_tick;
                prev_tick = tick;
                if (delta < 0)
                        delta = 0;
                ticks_left -= delta;
                if (doswitch && ticks_left > 0)
                        lwkt_switch();
                cpu_pause();
        }
#ifdef DELAYDEBUG
        if (state == 1)
                kprintf(" %d calls to getit() at %d usec each\n",
                        getit_calls, (n + 5) / getit_calls);
#endif
}

/*
 * DELAY() never switches.
 */
void
DELAY(int n)
{
        DODELAY(n, 0);
}

/*
 * Returns non-zero if the specified time period has elapsed.  Call
 * first with last_clock set to 0.
 */
int
CHECKTIMEOUT(TOTALDELAY *tdd)
{
        sysclock_t delta;
        int us;

        if (tdd->started == 0) {
                if (timer0_state == RELEASED && i8254_cputimer_disable == 0)
                        i8254_restore();
                tdd->last_clock = sys_cputimer->count();
                tdd->started = 1;
                return(0);
        }
        delta = sys_cputimer->count() - tdd->last_clock;
        us = muldivu64(delta, 1000000, sys_cputimer->freq);
        tdd->last_clock += muldivu64(us, sys_cputimer->freq, 1000000);
        tdd->us -= us;

        return (tdd->us < 0);
}


/*
 * DRIVERSLEEP() does not switch if called with a spinlock held or
 * from a hard interrupt.
 */
void
DRIVERSLEEP(int usec)
{
        globaldata_t gd = mycpu;

        if (gd->gd_intr_nesting_level || gd->gd_spinlocks) {
                DODELAY(usec, 0);
        } else {
                DODELAY(usec, 1);
        }
}

static void
sysbeepstop(void *chan)
{
        outb(IO_PPI, inb(IO_PPI)&0xFC); /* disable counter2 output to speaker */
        beeping = 0;
        release_timer2();
}

int
sysbeep(int pitch, int period)
{
        if (acquire_timer2(TIMER_SQWAVE|TIMER_16BIT))
                return(-1);
        if (sysbeep_enable == 0)
                return(-1);
        /*
         * Nobody else is using timer2, we do not need the clock lock
         */
        outb(TIMER_CNTR2, pitch);
        outb(TIMER_CNTR2, (pitch>>8));
        if (!beeping) {
                /* enable counter2 output to speaker */
                outb(IO_PPI, inb(IO_PPI) | 3);
                beeping = period;
                callout_reset(&sysbeepstop_ch, period, sysbeepstop, NULL);
        }
        return (0);
}

/*
 * RTC support routines
 */

int
rtcin(int reg)
{
        u_char val;

        crit_enter();
        outb(IO_RTC, reg);
        inb(0x84);
        val = inb(IO_RTC + 1);
        inb(0x84);
        crit_exit();
        return (val);
}

static __inline void
writertc(u_char reg, u_char val)
{
        crit_enter();
        inb(0x84);
        outb(IO_RTC, reg);
        inb(0x84);
        outb(IO_RTC + 1, val);
        inb(0x84);              /* XXX work around wrong order in rtcin() */
        crit_exit();
}

static __inline int
readrtc(int port)
{
        return(bcd2bin(rtcin(port)));
}

static u_int
calibrate_clocks(void)
{
        tsc_uclock_t old_tsc;
        sysclock_t tot_count;
        sysclock_t count, prev_count;
        int sec, start_sec, timeout;

        if (bootverbose)
                kprintf("Calibrating clock(s) ...\n");
        if (!(rtcin(RTC_STATUSD) & RTCSD_PWR))
                goto fail;
        timeout = 100000000;

        /* Read the mc146818A seconds counter. */
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP)) {
                        sec = rtcin(RTC_SEC);
                        break;
                }
                if (--timeout == 0)
                        goto fail;
        }

        /* Wait for the mC146818A seconds counter to change. */
        start_sec = sec;
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP)) {
                        sec = rtcin(RTC_SEC);
                        if (sec != start_sec)
                                break;
                }
                if (--timeout == 0)
                        goto fail;
        }

        /* Start keeping track of the i8254 counter. */
        prev_count = sys_cputimer->count();
        tot_count = 0;

        if (tsc_present)
                old_tsc = rdtsc();
        else
                old_tsc = 0;            /* shut up gcc */

        /*
         * Wait for the mc146818A seconds counter to change.  Read the i8254
         * counter for each iteration since this is convenient and only
         * costs a few usec of inaccuracy. The timing of the final reads
         * of the counters almost matches the timing of the initial reads,
         * so the main cause of inaccuracy is the varying latency from
         * inside getit() or rtcin(RTC_STATUSA) to the beginning of the
         * rtcin(RTC_SEC) that returns a changed seconds count.  The
         * maximum inaccuracy from this cause is < 10 usec on 486's.
         */
        start_sec = sec;
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP))
                        sec = rtcin(RTC_SEC);
                count = sys_cputimer->count();
                tot_count += (sysclock_t)(count - prev_count);
                prev_count = count;
                if (sec != start_sec)
                        break;
                if (--timeout == 0)
                        goto fail;
        }

        /*
         * Read the cpu cycle counter.  The timing considerations are
         * similar to those for the i8254 clock.
         */
        if (tsc_present) {
                tsc_frequency = rdtsc() - old_tsc;
                if (bootverbose) {
                        kprintf("TSC clock: %jd Hz (Method A)\n",
                            (intmax_t)tsc_frequency);
                }
        }
        tsc_oneus_approx = ((tsc_frequency|1) + 999999) / 1000000;

        kprintf("i8254 clock: %lu Hz\n", tot_count);
        return (tot_count);

fail:
        kprintf("failed, using default i8254 clock of %lu Hz\n",
                i8254_cputimer.freq);
        return (i8254_cputimer.freq);
}

static void
i8254_restore(void)
{
        timer0_state = ACQUIRED;

        clock_lock();

        /*
         * Timer0 is our fine-grained variable clock interrupt
         */
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
        outb(TIMER_CNTR0, 2);   /* lsb */
        outb(TIMER_CNTR0, 0);   /* msb */
        clock_unlock();

        if (!i8254_nointr) {
                cputimer_intr_register(&i8254_cputimer_intr);
                cputimer_intr_select(&i8254_cputimer_intr, 0);
        }

        /*
         * Timer1 or timer2 is our free-running clock, but only if another
         * has not been selected.
         */
        cputimer_register(&i8254_cputimer);
        cputimer_select(&i8254_cputimer, 0);
}

static void
i8254_cputimer_construct(struct cputimer *timer, sysclock_t oldclock)
{
        int which;

        /*
         * Should we use timer 1 or timer 2 ?
         */
        which = 0;
        TUNABLE_INT_FETCH("hw.i8254.walltimer", &which);
        if (which != 1 && which != 2)
                which = 2;

        switch(which) {
        case 1:
                timer->name = "i8254_timer1";
                timer->type = CPUTIMER_8254_SEL1;
                i8254_walltimer_sel = TIMER_SEL1;
                i8254_walltimer_cntr = TIMER_CNTR1;
                timer1_state = ACQUIRED;
                break;
        case 2:
                timer->name = "i8254_timer2";
                timer->type = CPUTIMER_8254_SEL2;
                i8254_walltimer_sel = TIMER_SEL2;
                i8254_walltimer_cntr = TIMER_CNTR2;
                timer2_state = ACQUIRED;
                break;
        }

        timer->base = (oldclock + 0xFFFF) & 0xFFFFFFFFFFFF0000LU;

        clock_lock();
        outb(TIMER_MODE, i8254_walltimer_sel | TIMER_RATEGEN | TIMER_16BIT);
        outb(i8254_walltimer_cntr, 0);  /* lsb */
        outb(i8254_walltimer_cntr, 0);  /* msb */
        outb(IO_PPI, inb(IO_PPI) | 1);  /* bit 0: enable gate, bit 1: spkr */
        clock_unlock();
}

static void
i8254_cputimer_destruct(struct cputimer *timer)
{
        switch(timer->type) {
        case CPUTIMER_8254_SEL1:
            timer1_state = RELEASED;
            break;
        case CPUTIMER_8254_SEL2:
            timer2_state = RELEASED;
            break;
        default:
            break;
        }
        timer->type = 0;
}

static void
rtc_restore(void)
{
        /* Restore all of the RTC's "status" (actually, control) registers. */
        writertc(RTC_STATUSB, RTCSB_24HR);
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, rtc_statusb);
}

/*
 * Restore all the timers.
 *
 * This function is called to resynchronize our core timekeeping after a
 * long halt, e.g. from apm_default_resume() and friends.  It is also
 * called if after a BIOS call we have detected munging of the 8254.
 * It is necessary because cputimer_count() counter's delta may have grown
 * too large for nanouptime() and friends to handle, or (in the case of 8254
 * munging) might cause the SYSTIMER code to prematurely trigger.
 */
void
timer_restore(void)
{
        crit_enter();
        if (i8254_cputimer_disable == 0)
                i8254_restore();        /* restore timer_freq and hz */
        rtc_restore();                  /* reenable RTC interrupts */
        crit_exit();
}

#define MAX_MEASURE_RETRIES     100

static u_int64_t
do_measure(u_int64_t timer_latency, u_int64_t *latency, sysclock_t *time,
    int *retries)
{
        u_int64_t tsc1, tsc2;
        u_int64_t threshold;
        sysclock_t val;
        int cnt = 0;

        do {
                if (cnt > MAX_MEASURE_RETRIES/2)
                        threshold = timer_latency << 1;
                else
                        threshold = timer_latency + (timer_latency >> 2);

                cnt++;
                tsc1 = rdtsc_ordered();
                val = sys_cputimer->count();
                tsc2 = rdtsc_ordered();
        } while (timer_latency > 0 && cnt < MAX_MEASURE_RETRIES &&
            tsc2 - tsc1 > threshold);

        *retries = cnt - 1;
        *latency = tsc2 - tsc1;
        *time = val;
        return tsc1;
}

static u_int64_t
do_calibrate_cputimer(u_int usecs, u_int64_t timer_latency)
{
        if (calibrate_tsc_fast) {
                u_int64_t old_tsc1, start_lat1, new_tsc1, end_lat1;
                u_int64_t old_tsc2, start_lat2, new_tsc2, end_lat2;
                u_int64_t freq1, freq2;
                sysclock_t start1, end1, start2, end2;
                int retries1, retries2, retries3, retries4;

                DELAY(1000);
                old_tsc1 = do_measure(timer_latency, &start_lat1, &start1,
                    &retries1);
                DELAY(20000);
                old_tsc2 = do_measure(timer_latency, &start_lat2, &start2,
                    &retries2);
                DELAY(usecs);
                new_tsc1 = do_measure(timer_latency, &end_lat1, &end1,
                    &retries3);
                DELAY(20000);
                new_tsc2 = do_measure(timer_latency, &end_lat2, &end2,
                    &retries4);

                old_tsc1 += start_lat1;
                old_tsc2 += start_lat2;
                freq1 = (new_tsc1 - old_tsc1) + (start_lat1 + end_lat1) / 2;
                freq2 = (new_tsc2 - old_tsc2) + (start_lat2 + end_lat2) / 2;
                end1 -= start1;
                end2 -= start2;
                /* This should in practice be safe from overflows. */
                freq1 = muldivu64(freq1, sys_cputimer->freq, end1);
                freq2 = muldivu64(freq2, sys_cputimer->freq, end2);
                if (calibrate_test && (retries1 > 0 || retries2 > 0)) {
                        kprintf("%s: retries: %d, %d, %d, %d\n",
                            __func__, retries1, retries2, retries3, retries4);
                }
                if (calibrate_test) {
                        kprintf("%s: freq1=%ju freq2=%ju avg=%ju\n",
                            __func__, freq1, freq2, (freq1 + freq2) / 2);
                }
                return (freq1 + freq2) / 2;
        } else {
                u_int64_t old_tsc, new_tsc;
                u_int64_t freq;

                old_tsc = rdtsc_ordered();
                DELAY(usecs);
                new_tsc = rdtsc();
                freq = new_tsc - old_tsc;
                /* This should in practice be safe from overflows. */
                freq = (freq * 1000 * 1000) / usecs;
                return freq;
        }
}

/*
 * Initialize 8254 timer 0 early so that it can be used in DELAY().
 */
void
startrtclock(void)
{
        const timecounter_init_t **list;
        sysclock_t delta, freq;
        int forced_invariant = 0;

        callout_init_mp(&sysbeepstop_ch);

        /*
         * Can we use the TSC?
         *
         * NOTE: If running under qemu, probably a good idea to force the
         *       TSC because we are not likely to detect it as being
         *       invariant or mpsyncd if you don't.  This will greatly
         *       reduce SMP contention.
         */
        if (cpu_feature & CPUID_TSC) {
                tsc_present = 1;
                TUNABLE_INT_FETCH("hw.tsc_cputimer_force", &tsc_invariant);
                forced_invariant = tsc_invariant;

                if ((cpu_vendor_id == CPU_VENDOR_INTEL ||
                     cpu_vendor_id == CPU_VENDOR_AMD) &&
                    cpu_exthigh >= 0x80000007) {
                        u_int regs[4];

                        do_cpuid(0x80000007, regs);
                        if (regs[3] & 0x100) {
                                tsc_invariant = 1;
                                forced_invariant = 0;
                        }
                }
        } else {
                tsc_present = 0;
        }

        /*
         * Initial RTC state, don't do anything unexpected
         */
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, RTCSB_24HR);

        SET_FOREACH(list, timecounter_init_set) {
                if ((*list)->configure != NULL)
                        (*list)->configure();
        }

        /*
         * If tsc_frequency is already initialized now, and a flag is set
         * that i8254 timer is unneeded, we are done.
         */
        if (tsc_frequency != 0 && i8254_cputimer_disable != 0)
                goto done;

        /*
         * Set the 8254 timer0 in TIMER_SWSTROBE mode and cause it to
         * generate an interrupt, which we will ignore for now.
         *
         * Set the 8254 timer1 in TIMER_RATEGEN mode and load 0x0000
         * (so it counts a full 2^16 and repeats).  We will use this timer
         * for our counting.
         */
        if (i8254_cputimer_disable == 0)
                i8254_restore();

        kprintf("Using cputimer %s for TSC calibration\n", sys_cputimer->name);

        /*
         * When booting without verbose messages, it's pointless to run the
         * calibrate_clocks() calibration code, when we don't use the
         * results in any way. With bootverbose, we are at least printing
         *  this information to the kernel log.
         */
        if (i8254_cputimer_disable != 0 ||
            (calibrate_timers_with_rtc == 0 && !bootverbose)) {
                goto skip_rtc_based;
        }

        freq = calibrate_clocks();
#ifdef CLK_CALIBRATION_LOOP
        if (bootverbose) {
                int c;

                cnpoll(TRUE);
                kprintf("Press a key on the console to "
                        "abort clock calibration\n");
                while ((c = cncheckc()) == -1 || c == NOKEY)
                        calibrate_clocks();
                cnpoll(FALSE);
        }
#endif

        /*
         * Use the calibrated i8254 frequency if it seems reasonable.
         * Otherwise use the default, and don't use the calibrated i586
         * frequency.
         */
        delta = freq > i8254_cputimer.freq ?
                freq - i8254_cputimer.freq : i8254_cputimer.freq - freq;
        if (delta < i8254_cputimer.freq / 100) {
                if (calibrate_timers_with_rtc == 0) {
                        kprintf(
"hw.calibrate_timers_with_rtc not set - using default i8254 frequency\n");
                        freq = i8254_cputimer.freq;
                }
                /*
                 * NOTE:
                 * Interrupt timer's freq must be adjusted
                 * before we change the cuptimer's frequency.
                 */
                i8254_cputimer_intr.freq = freq;
                cputimer_set_frequency(&i8254_cputimer, freq);
        } else {
                if (bootverbose)
                        kprintf("%lu Hz differs from default of %lu Hz "
                                "by more than 1%%\n",
                                freq, i8254_cputimer.freq);
                tsc_frequency = 0;
        }

        if (tsc_frequency != 0 && calibrate_timers_with_rtc == 0) {
                kprintf("hw.calibrate_timers_with_rtc not "
                        "set - using old calibration method\n");
                tsc_frequency = 0;
        }

skip_rtc_based:
        if (tsc_present && tsc_frequency == 0) {
                u_int cnt;
                u_int64_t cputime_latency_tsc = 0, max = 0, min = 0;
                int i;

                for (i = 0; i < 10; i++) {
                        /* Warm up */
                        (void)sys_cputimer->count();
                }
                for (i = 0; i < 100; i++) {
                        u_int64_t old_tsc, new_tsc;

                        old_tsc = rdtsc_ordered();
                        (void)sys_cputimer->count();
                        new_tsc = rdtsc_ordered();
                        cputime_latency_tsc += (new_tsc - old_tsc);
                        if (max < (new_tsc - old_tsc))
                                max = new_tsc - old_tsc;
                        if (min == 0 || min > (new_tsc - old_tsc))
                                min = new_tsc - old_tsc;
                }
                cputime_latency_tsc /= 100;
                kprintf(
                    "Timer latency (in TSC ticks): %lu min=%lu max=%lu\n",
                    cputime_latency_tsc, min, max);
                /* XXX Instead of this, properly filter out outliers. */
                cputime_latency_tsc = min;

                if (calibrate_test > 0) {
                        u_int64_t values[20], avg = 0;
                        for (i = 1; i <= 20; i++) {
                                u_int64_t freq;

                                freq = do_calibrate_cputimer(i * 100 * 1000,
                                    cputime_latency_tsc);
                                values[i - 1] = freq;
                        }
                        /* Compute an average TSC for the 1s to 2s delays. */
                        for (i = 10; i < 20; i++)
                                avg += values[i];
                        avg /= 10;
                        for (i = 0; i < 20; i++) {
                                kprintf("%ums: %lu (Diff from average: %ld)\n",
                                    (i + 1) * 100, values[i],
                                    (int64_t)(values[i] - avg));
                        }
                }

                if (calibrate_tsc_fast > 0) {
                        /* HPET would typically be >10MHz */
                        if (sys_cputimer->freq >= 10000000)
                                cnt = 200000;
                        else
                                cnt = 500000;
                } else {
                        cnt = 1000000;
                }

                tsc_frequency = do_calibrate_cputimer(cnt, cputime_latency_tsc);
                if (bootverbose && calibrate_timers_with_rtc) {
                        kprintf("TSC clock: %jd Hz (Method B)\n",
                            (intmax_t)tsc_frequency);
                }
        }

done:
        if (tsc_present) {
                kprintf("TSC clock: %jd Hz, %sinvariant%s\n",
                        (intmax_t)tsc_frequency,
                        tsc_invariant ? "" : "NOT ",
                        forced_invariant ? " (forced)" : "");
        }
        tsc_oneus_approx = ((tsc_frequency|1) + 999999) / 1000000;

        EVENTHANDLER_REGISTER(shutdown_post_sync, resettodr_on_shutdown,
                              NULL, SHUTDOWN_PRI_LAST);
}

/*
 * Sync the time of day back to the RTC on shutdown, but only if
 * we have already loaded it and have not crashed.
 */
static void
resettodr_on_shutdown(void *arg __unused)
{
        if (rtc_loaded && panicstr == NULL) {
                resettodr();
        }
}

/*
 * Initialize the time of day register, based on the time base which is, e.g.
 * from a filesystem.
 */
void
inittodr(time_t base)
{
        time_t          sec, days;
        int             year, month;
        int             y, m;
        struct timespec ts;

        if (base) {
                ts.tv_sec = base;
                ts.tv_nsec = 0;
                set_timeofday(&ts);
        }

        /* Look if we have a RTC present and the time is valid */
        if (!(rtcin(RTC_STATUSD) & RTCSD_PWR))
                goto wrong_time;

        /* wait for time update to complete */
        /* If RTCSA_TUP is zero, we have at least 244us before next update */
        crit_enter();
        while (rtcin(RTC_STATUSA) & RTCSA_TUP) {
                crit_exit();
                crit_enter();
        }

        days = 0;
#ifdef USE_RTC_CENTURY
        year = readrtc(RTC_YEAR) + readrtc(RTC_CENTURY) * 100;
#else
        year = readrtc(RTC_YEAR) + 1900;
        if (year < 1970)
                year += 100;
#endif
        if (year < 1970) {
                crit_exit();
                goto wrong_time;
        }
        month = readrtc(RTC_MONTH);
        for (m = 1; m < month; m++)
                days += daysinmonth[m-1];
        if ((month > 2) && LEAPYEAR(year))
                days ++;
        days += readrtc(RTC_DAY) - 1;
        for (y = 1970; y < year; y++)
                days += DAYSPERYEAR + LEAPYEAR(y);
        sec = ((( days * 24 +
                  readrtc(RTC_HRS)) * 60 +
                  readrtc(RTC_MIN)) * 60 +
                  readrtc(RTC_SEC));
        /* sec now contains the number of seconds, since Jan 1 1970,
           in the local time zone */

        sec += tz.tz_minuteswest * 60 + (wall_cmos_clock ? adjkerntz : 0);

        if (time_second <= sec - 2 || time_second >= sec + 2) {
                /* badly off, adjust it */
                ts.tv_sec = sec;
                ts.tv_nsec = 0;
                set_timeofday(&ts);
        }
        rtc_loaded = 1;
        crit_exit();
        return;

wrong_time:
        kprintf("Invalid time in real time clock.\n");
        kprintf("Check and reset the date immediately!\n");
}

/*
 * Write system time back to RTC
 */
void
resettodr(void)
{
        struct timeval tv;
        unsigned long tm;
        int m;
        int y;

        if (disable_rtc_set)
                return;

        microtime(&tv);
        tm = tv.tv_sec;

        crit_enter();
        /* Disable RTC updates and interrupts. */
        writertc(RTC_STATUSB, RTCSB_HALT | RTCSB_24HR);

        /* Calculate local time to put in RTC */

        tm -= tz.tz_minuteswest * 60 + (wall_cmos_clock ? adjkerntz : 0);

        writertc(RTC_SEC, bin2bcd(tm%60)); tm /= 60;    /* Write back Seconds */
        writertc(RTC_MIN, bin2bcd(tm%60)); tm /= 60;    /* Write back Minutes */
        writertc(RTC_HRS, bin2bcd(tm%24)); tm /= 24;    /* Write back Hours   */

        /* We have now the days since 01-01-1970 in tm */
        writertc(RTC_WDAY, (tm+4)%7);                   /* Write back Weekday */
        for (y = 1970, m = DAYSPERYEAR + LEAPYEAR(y);
             tm >= m;
             y++,      m = DAYSPERYEAR + LEAPYEAR(y))
             tm -= m;

        /* Now we have the years in y and the day-of-the-year in tm */
        writertc(RTC_YEAR, bin2bcd(y%100));             /* Write back Year    */
#ifdef USE_RTC_CENTURY
        writertc(RTC_CENTURY, bin2bcd(y/100));          /* ... and Century    */
#endif
        for (m = 0; ; m++) {
                int ml;

                ml = daysinmonth[m];
                if (m == 1 && LEAPYEAR(y))
                        ml++;
                if (tm < ml)
                        break;
                tm -= ml;
        }

        writertc(RTC_MONTH, bin2bcd(m + 1));            /* Write back Month   */
        writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */

        /* Reenable RTC updates and interrupts. */
        writertc(RTC_STATUSB, rtc_statusb);
        crit_exit();
}

static int
i8254_ioapic_trial(int irq, struct cputimer_intr *cti)
{
        sysclock_t base;
        long lastcnt;

        /*
         * Following code assumes the 8254 is the cpu timer,
         * so make sure it is.
         */
        /*KKASSERT(sys_cputimer == &i8254_cputimer); (tested by CuteLarva) */
        KKASSERT(cti == &i8254_cputimer_intr);

        lastcnt = get_interrupt_counter(irq, mycpuid);

        /*
         * Force an 8254 Timer0 interrupt and wait 1/100s for
         * it to happen, then see if we got it.
         */
        kprintf("IOAPIC: testing 8254 interrupt delivery...");

        i8254_intr_reload(cti, sys_cputimer->fromus(2));
        base = sys_cputimer->count();
        while (sys_cputimer->count() - base < sys_cputimer->freq / 100)
                ; /* nothing */

        if (get_interrupt_counter(irq, mycpuid) - lastcnt == 0) {
                kprintf(" failed\n");
                return ENOENT;
        } else {
                kprintf(" success\n");
        }
        return 0;
}

/*
 * Start both clocks running.  DragonFly note: the stat clock is no longer
 * used.  Instead, 8254 based systimers are used for all major clock
 * interrupts.
 */
static void
i8254_intr_initclock(struct cputimer_intr *cti, boolean_t selected)
{
        void *clkdesc = NULL;
        int irq = 0, mixed_mode = 0, error;

        KKASSERT(mycpuid == 0);

        if (!selected && i8254_intr_disable)
                goto nointr;

        /*
         * The stat interrupt mask is different without the
         * statistics clock.  Also, don't set the interrupt
         * flag which would normally cause the RTC to generate
         * interrupts.
         */
        rtc_statusb = RTCSB_24HR;

        /* Finish initializing 8254 timer 0. */
        if (ioapic_enable) {
                irq = machintr_legacy_intr_find(0, INTR_TRIGGER_EDGE,
                        INTR_POLARITY_HIGH);
                if (irq < 0) {
mixed_mode_setup:
                        error = ioapic_conf_legacy_extint(0);
                        if (!error) {
                                irq = machintr_legacy_intr_find(0,
                                    INTR_TRIGGER_EDGE, INTR_POLARITY_HIGH);
                                if (irq < 0)
                                        error = ENOENT;
                        }

                        if (error) {
                                if (!selected) {
                                        kprintf("IOAPIC: setup mixed mode for "
                                                "irq 0 failed: %d\n", error);
                                        goto nointr;
                                } else {
                                        panic("IOAPIC: setup mixed mode for "
                                              "irq 0 failed: %d\n", error);
                                }
                        }
                        mixed_mode = 1;
                }
                clkdesc = register_int(irq, clkintr, NULL, "clk",
                                       NULL,
                                       INTR_EXCL | INTR_CLOCK |
                                       INTR_NOPOLL | INTR_MPSAFE |
                                       INTR_NOENTROPY, 0);
        } else {
                register_int(0, clkintr, NULL, "clk", NULL,
                             INTR_EXCL | INTR_CLOCK |
                             INTR_NOPOLL | INTR_MPSAFE |
                             INTR_NOENTROPY, 0);
        }

        /* Initialize RTC. */
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, RTCSB_24HR);

        if (ioapic_enable) {
                error = i8254_ioapic_trial(irq, cti);
                if (error) {
                        if (mixed_mode) {
                                if (!selected) {
                                        kprintf("IOAPIC: mixed mode for irq %d "
                                                "trial failed: %d\n",
                                                irq, error);
                                        goto nointr;
                                } else {
                                        panic("IOAPIC: mixed mode for irq %d "
                                              "trial failed: %d\n", irq, error);
                                }
                        } else {
                                kprintf("IOAPIC: warning 8254 is not connected "
                                        "to the correct pin, try mixed mode\n");
                                unregister_int(clkdesc, 0);
                                goto mixed_mode_setup;
                        }
                }
        }
        return;

nointr:
        i8254_nointr = 1; /* don't try to register again */
        cputimer_intr_deregister(cti);
}

void
setstatclockrate(int newhz)
{
        if (newhz == RTC_PROFRATE)
                rtc_statusa = RTCSA_DIVIDER | RTCSA_PROF;
        else
                rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
        writertc(RTC_STATUSA, rtc_statusa);
}

#if 0
static unsigned
tsc_get_timecount(struct timecounter *tc)
{
        return (rdtsc());
}
#endif

#ifdef KERN_TIMESTAMP
#define KERN_TIMESTAMP_SIZE 16384
static u_long tsc[KERN_TIMESTAMP_SIZE] ;
SYSCTL_OPAQUE(_debug, OID_AUTO, timestamp, CTLFLAG_RD, tsc,
        sizeof(tsc), "LU", "Kernel timestamps");
void
_TSTMP(u_int32_t x)
{
        static int i;

        tsc[i] = (u_int32_t)rdtsc();
        tsc[i+1] = x;
        i = i + 2;
        if (i >= KERN_TIMESTAMP_SIZE)
                i = 0;
        tsc[i] = 0; /* mark last entry */
}
#endif /* KERN_TIMESTAMP */

static int
hw_i8254_timestamp(SYSCTL_HANDLER_ARGS)
{
        sysclock_t count;
        uint64_t tscval;
        char buf[32];

        crit_enter();
        if (sys_cputimer == &i8254_cputimer)
                count = sys_cputimer->count();
        else
                count = 0;
        if (tsc_present)
                tscval = rdtsc();
        else
                tscval = 0;
        crit_exit();

        ksnprintf(buf, sizeof(buf), "%016lx %016lx", count, tscval);
        return(SYSCTL_OUT(req, buf, strlen(buf) + 1));
}

struct tsc_mpsync_info {
        volatile int            tsc_ready_cnt;
        volatile int            tsc_done_cnt;
        volatile int            tsc_command;
        volatile int            unused01[5];
        struct {
                uint64_t        v;
                uint64_t        unused02;
        } tsc_saved[MAXCPU];
} __cachealign;

#if 0
static void
tsc_mpsync_test_loop(struct tsc_mpsync_thr *info)
{
        struct globaldata *gd = mycpu;
        tsc_uclock_t test_end, test_begin;
        u_int i;

        if (bootverbose) {
                kprintf("cpu%d: TSC testing MP synchronization ...\n",
                    gd->gd_cpuid);
        }

        test_begin = rdtsc_ordered();
        /* Run test for 100ms */
        test_end = test_begin + (tsc_frequency / 10);

        arg->tsc_mpsync = 1;
        arg->tsc_target = test_begin;

#define TSC_TEST_TRYMAX         1000000 /* Make sure we could stop */
#define TSC_TEST_TRYMIN         50000

        for (i = 0; i < TSC_TEST_TRYMAX; ++i) {
                struct lwkt_cpusync cs;

                crit_enter();
                lwkt_cpusync_init(&cs, gd->gd_other_cpus,
                    tsc_mpsync_test_remote, arg);
                lwkt_cpusync_interlock(&cs);
                cpu_pause();
                arg->tsc_target = rdtsc_ordered();
                cpu_mfence();
                lwkt_cpusync_deinterlock(&cs);
                crit_exit();
                cpu_pause();

                if (!arg->tsc_mpsync) {
                        kprintf("cpu%d: TSC is not MP synchronized @%u\n",
                            gd->gd_cpuid, i);
                        break;
                }
                if (arg->tsc_target > test_end && i >= TSC_TEST_TRYMIN)
                        break;
        }

#undef TSC_TEST_TRYMIN
#undef TSC_TEST_TRYMAX

        if (arg->tsc_target == test_begin) {
                kprintf("cpu%d: TSC does not tick?!\n", gd->gd_cpuid);
                /* XXX disable TSC? */
                tsc_invariant = 0;
                arg->tsc_mpsync = 0;
                return;
        }

        if (arg->tsc_mpsync && bootverbose) {
                kprintf("cpu%d: TSC is MP synchronized after %u tries\n",
                    gd->gd_cpuid, i);
        }
}

#endif

#define TSC_TEST_COUNT          50000

static void
tsc_mpsync_ap_thread(void *xinfo)
{
        struct tsc_mpsync_info *info = xinfo;
        int cpu = mycpuid;
        int i;

        /*
         * Tell main loop that we are ready and wait for initiation
         */
        atomic_add_int(&info->tsc_ready_cnt, 1);
        while (info->tsc_command == 0) {
                lwkt_force_switch();
        }

        /*
         * Run test for 10000 loops or until tsc_done_cnt != 0 (another
         * cpu has finished its test), then increment done.
         */
        crit_enter();
        for (i = 0; i < TSC_TEST_COUNT && info->tsc_done_cnt == 0; ++i) {
                info->tsc_saved[cpu].v = rdtsc_ordered();
        }
        crit_exit();
        atomic_add_int(&info->tsc_done_cnt, 1);

        lwkt_exit();
}

static void
tsc_mpsync_test(void)
{
        enum { TSCOK, TSCNEG, TSCSPAN } error = TSCOK;
        int cpu;
        int try;

        if (!tsc_invariant) {
                /* Not even invariant TSC */
                kprintf("TSC is not invariant, "
                        "no further tests will be performed\n");
                return;
        }

        if (ncpus == 1) {
                /* Only one CPU */
                tsc_mpsync = 1;
                return;
        }

        /*
         * Forcing can be used w/qemu to reduce contention
         */
        TUNABLE_INT_FETCH("hw.tsc_cputimer_force", &tsc_mpsync);

        if (tsc_mpsync == 0) {
                switch (cpu_vendor_id) {
                case CPU_VENDOR_INTEL:
                        /*
                         * Intel probably works
                         */
                        break;

                case CPU_VENDOR_AMD:
                        /*
                         * For AMD 15h and 16h (i.e. The Bulldozer and Jaguar
                         * architectures) we have to watch out for
                         * Erratum 778:
                         *     "Processor Core Time Stamp Counters May
                         *      Experience Drift"
                         * This Erratum is only listed for cpus in Family
                         * 15h < Model 30h and for 16h < Model 30h.
                         *
                         * AMD < Bulldozer probably doesn't work
                         */
                        if (CPUID_TO_FAMILY(cpu_id) == 0x15 ||
                            CPUID_TO_FAMILY(cpu_id) == 0x16) {
                                if (CPUID_TO_MODEL(cpu_id) < 0x30)
                                        return;
                        } else if (CPUID_TO_FAMILY(cpu_id) < 0x17) {
                                return;
                        }
                        break;

                default:
                        /* probably won't work */
                        return;
                }
        } else if (tsc_mpsync < 0) {
                kprintf("TSC MP synchronization test is disabled\n");
                tsc_mpsync = 0;
                return;
        }

        /*
         * Test even if forced to 1 above.  If forced, we will use the TSC
         * even if the test fails.  (set forced to -1 to disable entirely).
         */
        kprintf("TSC testing MP synchronization ...\n");
        kprintf("TSC testing MP: NOTE! CPU pwrsave will inflate latencies!\n");

        /*
         * Test that the TSC is monotonically increasing across CPU
         * switches.  Otherwise time will get really messed up if the
         * TSC is selected as the timebase.
         *
         * Test 4 times
         */
        for (try = 0; tsc_frequency && try < 4; ++try) {
                tsc_uclock_t last;
                tsc_uclock_t next;
                tsc_sclock_t delta;
                tsc_sclock_t lo_delta = 0x7FFFFFFFFFFFFFFFLL;
                tsc_sclock_t hi_delta = -0x7FFFFFFFFFFFFFFFLL;

                last = rdtsc();
                for (cpu = 0; cpu < ncpus; ++cpu) {
                        lwkt_migratecpu(cpu);
                        next = rdtsc();
                        if (cpu == 0) {
                                last = next;
                                continue;
                        }

                        delta = next - last;
                        if (delta < 0) {
                                kprintf("TSC cpu-delta NEGATIVE: "
                                        "cpu %d to %d (%ld)\n",
                                        cpu - 1, cpu, delta);
                                error = TSCNEG;
                        }
                        if (lo_delta > delta)
                                lo_delta = delta;
                        if (hi_delta < delta)
                                hi_delta = delta;
                        last = next;
                }
                last = rdtsc();
                for (cpu = ncpus - 2; cpu >= 0; --cpu) {
                        lwkt_migratecpu(cpu);
                        next = rdtsc();
                        delta = next - last;
                        if (delta <= 0) {
                                kprintf("TSC cpu-delta WAS NEGATIVE! "
                                        "cpu %d to %d (%ld)\n",
                                        cpu + 1, cpu, delta);
                                error = TSCNEG;
                        }
                        if (lo_delta > delta)
                                lo_delta = delta;
                        if (hi_delta < delta)
                                hi_delta = delta;
                        last = next;
                }
                kprintf("TSC cpu-delta test complete, %ldns to %ldns ",
                        muldivu64(lo_delta, 1000000000, tsc_frequency),
                        muldivu64(hi_delta, 1000000000, tsc_frequency));
                if (error != TSCOK) {
                        kprintf("FAILURE\n");
                        break;
                }
                kprintf("SUCCESS\n");
        }

        /*
         * Test TSC MP synchronization on APs.
         *
         * Test 4 times.
         */
        for (try = 0; tsc_frequency && try < 4; ++try) {
                struct tsc_mpsync_info info;
                uint64_t last;
                int64_t xworst;
                int64_t xdelta;
                int64_t delta;

                bzero(&info, sizeof(info));

                for (cpu = 0; cpu < ncpus; ++cpu) {
                        thread_t td;
                        lwkt_create(tsc_mpsync_ap_thread, &info, &td,
                                    NULL, TDF_NOSTART, cpu,
                                    "tsc mpsync %d", cpu);
                        lwkt_setpri_initial(td, curthread->td_pri);
                        lwkt_schedule(td);
                }
                while (info.tsc_ready_cnt != ncpus)
                        lwkt_force_switch();

                /*
                 * All threads are ready, start the test and wait for
                 * completion.
                 */
                info.tsc_command = 1;
                while (info.tsc_done_cnt != ncpus)
                        lwkt_force_switch();

                /*
                 * Process results
                 */
                last = info.tsc_saved[0].v;
                delta = 0;
                xworst = 0;
                for (cpu = 0; cpu < ncpus; ++cpu) {
                        xdelta = (int64_t)(info.tsc_saved[cpu].v - last);
                        last = info.tsc_saved[cpu].v;
                        if (xdelta < 0)
                                xdelta = -xdelta;
                        if (xworst < xdelta)
                                xworst = xdelta;
                        delta += xdelta;

                }

                /*
                 * Result from attempt.  Break-out if we succeeds, otherwise
                 * try again (up to 4 times).  This might be in a VM so we
                 * need to be robust.
                 */
                kprintf("TSC cpu concurrency test complete, worst=%ldns, "
                        "avg=%ldns ",
                        muldivu64(xworst, 1000000000, tsc_frequency),
                        muldivu64(delta / ncpus, 1000000000, tsc_frequency));
                if (delta / ncpus > tsc_frequency / 100) {
                        kprintf("FAILURE\n");
                }
                if (delta / ncpus < tsc_frequency / 100000) {
                        kprintf("SUCCESS\n");
                        if (error == TSCOK)
                                tsc_mpsync = 1;
                        break;
                }
                kprintf("INDETERMINATE\n");
        }

        if (tsc_mpsync)
                kprintf("TSC is MP synchronized\n");
        else
                kprintf("TSC is not MP synchronized\n");
}
SYSINIT(tsc_mpsync, SI_BOOT2_FINISH_SMP, SI_ORDER_ANY, tsc_mpsync_test, NULL);

static SYSCTL_NODE(_hw, OID_AUTO, i8254, CTLFLAG_RW, 0, "I8254");
SYSCTL_UINT(_hw_i8254, OID_AUTO, freq, CTLFLAG_RD, &i8254_cputimer.freq, 0,
            "frequency");
SYSCTL_PROC(_hw_i8254, OID_AUTO, timestamp, CTLTYPE_STRING|CTLFLAG_RD,
            0, 0, hw_i8254_timestamp, "A", "");

SYSCTL_INT(_hw, OID_AUTO, tsc_present, CTLFLAG_RD,
            &tsc_present, 0, "TSC Available");
SYSCTL_INT(_hw, OID_AUTO, tsc_invariant, CTLFLAG_RD,
            &tsc_invariant, 0, "Invariant TSC");
SYSCTL_INT(_hw, OID_AUTO, tsc_mpsync, CTLFLAG_RD,
            &tsc_mpsync, 0, "TSC is synchronized across CPUs");
SYSCTL_QUAD(_hw, OID_AUTO, tsc_frequency, CTLFLAG_RD,
            &tsc_frequency, 0, "TSC Frequency");