xref: /freebsd-11-stable/sys/x86/x86/delay.c

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * Copyright (c) 2010 Alexander Motin <mav@FreeBSD.org>
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz and Don Ahn.
 *
 * 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.
 * 4. 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
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/sys/x86/x86/delay.c 263008 2014-03-11 10:20:42Z royger $");

/* Generic x86 routines to handle delay */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/timetc.h>
#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/sched.h>

#include <machine/clock.h>
#include <machine/cpu.h>
#include <x86/init.h>

static u_int
get_tsc(__unused struct timecounter *tc)
{

	return (rdtsc32());
}

static int
delay_tc(int n)
{
	struct timecounter *tc;
	timecounter_get_t *func;
	uint64_t end, freq, now;
	u_int last, mask, u;

	tc = timecounter;
	freq = atomic_load_acq_64(&tsc_freq);
	if (tsc_is_invariant && freq != 0) {
		func = get_tsc;
		mask = ~0u;
	} else {
		if (tc->tc_quality <= 0)
			return (0);
		func = tc->tc_get_timecount;
		mask = tc->tc_counter_mask;
		freq = tc->tc_frequency;
	}
	now = 0;
	end = freq * n / 1000000;
	if (func == get_tsc)
		sched_pin();
	last = func(tc) & mask;
	do {
		cpu_spinwait();
		u = func(tc) & mask;
		if (u < last)
			now += mask - last + u + 1;
		else
			now += u - last;
		last = u;
	} while (now < end);
	if (func == get_tsc)
		sched_unpin();
	return (1);
}

void
DELAY(int n)
{

	if (delay_tc(n))
		return;

	init_ops.early_delay(n);
}