udelay.c

/*
 * This file is part of the flashrom project.
 *
 * Copyright (C) 2000 Silicon Integrated System Corporation
 * Copyright (C) 2009,2010 Carl-Daniel Hailfinger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#ifndef __LIBPAYLOAD__

#include <stdbool.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
#include <sys/time.h>
#include <stdlib.h>
#include <limits.h>
#include "flash.h"

static bool use_clock_gettime = false;

#if HAVE_CLOCK_GETTIME == 1

#ifdef _POSIX_MONOTONIC_CLOCK
static clockid_t clock_id = CLOCK_MONOTONIC;
#else
static clockid_t clock_id = CLOCK_REALTIME;
#endif

static void clock_usec_delay(int usecs)
{
	struct timespec now;
	clock_gettime(clock_id, &now);

	const long end_nsec = now.tv_nsec + usecs * 1000L;
	const struct timespec end = {
		end_nsec / (1000 * 1000 * 1000) + now.tv_sec,
		end_nsec % (1000 * 1000 * 1000)
	};
	do {
		clock_gettime(clock_id, &now);
	} while (now.tv_sec < end.tv_sec || (now.tv_sec == end.tv_sec && now.tv_nsec < end.tv_nsec));
}

static int clock_check_res(void)
{
	struct timespec res;
	if (!clock_getres(clock_id, &res)) {
		if (res.tv_sec == 0 && res.tv_nsec <= 100) {
			msg_pinfo("Using clock_gettime for delay loops (clk_id: %d, resolution: %ldns).\n",
				  (int)clock_id, res.tv_nsec);
			use_clock_gettime = true;
			return 1;
		}
	} else if (clock_id != CLOCK_REALTIME && errno == EINVAL) {
		/* Try again with CLOCK_REALTIME. */
		clock_id = CLOCK_REALTIME;
		return clock_check_res();
	}
	return 0;
}
#else

static inline void clock_usec_delay(int usecs) {}
static inline int clock_check_res(void) { return 0; }

#endif /* HAVE_CLOCK_GETTIME == 1 */

/* loops per microsecond */
static unsigned long micro = 1;

__attribute__ ((noinline)) void myusec_delay(unsigned int usecs)
{
	unsigned long i;
	for (i = 0; i < usecs * micro; i++) {
		/* Make sure the compiler doesn't optimize the loop away. */
		__asm__ volatile ("" : : "rm" (i) );
	}
}

static unsigned long measure_os_delay_resolution(void)
{
	unsigned long timeusec;
	struct timeval start, end;
	unsigned long counter = 0;

	gettimeofday(&start, NULL);
	timeusec = 0;

	while (!timeusec && (++counter < 1000000000)) {
		gettimeofday(&end, NULL);
		timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
			   (end.tv_usec - start.tv_usec);
		/* Protect against time going forward too much. */
		if ((end.tv_sec > start.tv_sec) &&
		    ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
			timeusec = 0;
		/* Protect against time going backwards during leap seconds. */
		if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
			timeusec = 0;
	}
	return timeusec;
}

static unsigned long measure_delay(unsigned int usecs)
{
	unsigned long timeusec;
	struct timeval start, end;

	gettimeofday(&start, NULL);
	myusec_delay(usecs);
	gettimeofday(&end, NULL);
	timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
		   (end.tv_usec - start.tv_usec);
	/* Protect against time going forward too much. */
	if ((end.tv_sec > start.tv_sec) &&
	    ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
		timeusec = LONG_MAX;
	/* Protect against time going backwards during leap seconds. */
	if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
		timeusec = 1;

	return timeusec;
}

void myusec_calibrate_delay(void)
{
	if (clock_check_res())
		return;

	unsigned long count = 1000;
	unsigned long timeusec, resolution;
	int i, tries = 0;

	msg_pinfo("Calibrating delay loop... ");
	resolution = measure_os_delay_resolution();
	if (resolution) {
		msg_pdbg("OS timer resolution is %lu usecs, ", resolution);
	} else {
		msg_pinfo("OS timer resolution is unusable. ");
	}

recalibrate:
	count = 1000;
	while (1) {
		timeusec = measure_delay(count);
		if (timeusec > 1000000 / 4)
			break;
		if (count >= ULONG_MAX / 2) {
			msg_pinfo("timer loop overflow, reduced precision. ");
			break;
		}
		count *= 2;
	}
	tries ++;

	/* Avoid division by zero, but in that case the loop is shot anyway. */
	if (!timeusec)
		timeusec = 1;

	/* Compute rounded up number of loops per microsecond. */
	micro = (count * micro) / timeusec + 1;
	msg_pdbg("%luM loops per second, ", micro);

	/* Did we try to recalibrate less than 5 times? */
	if (tries < 5) {
		/* Recheck our timing to make sure we weren't just hitting
		 * a scheduler delay or something similar.
		 */
		for (i = 0; i < 4; i++) {
			if (resolution && (resolution < 10)) {
				timeusec = measure_delay(100);
			} else if (resolution &&
				   (resolution < ULONG_MAX / 200)) {
				timeusec = measure_delay(resolution * 10) *
					   100 / (resolution * 10);
			} else {
				/* This workaround should be active for broken
				 * OS and maybe libpayload. The criterion
				 * here is horrible or non-measurable OS timer
				 * resolution which will result in
				 * measure_delay(100)=0 whereas a longer delay
				 * (1000 ms) may be sufficient
				 * to get a nonzero time measurement.
				 */
				timeusec = measure_delay(1000000) / 10000;
			}
			if (timeusec < 90) {
				msg_pdbg("delay more than 10%% too short (got "
					 "%lu%% of expected delay), "
					 "recalculating... ", timeusec);
				goto recalibrate;
			}
		}
	} else {
		msg_perr("delay loop is unreliable, trying to continue ");
	}

	/* We're interested in the actual precision. */
	timeusec = measure_delay(10);
	msg_pdbg("10 myus = %ld us, ", timeusec);
	timeusec = measure_delay(100);
	msg_pdbg("100 myus = %ld us, ", timeusec);
	timeusec = measure_delay(1000);
	msg_pdbg("1000 myus = %ld us, ", timeusec);
	timeusec = measure_delay(10000);
	msg_pdbg("10000 myus = %ld us, ", timeusec);
	timeusec = measure_delay(resolution * 4);
	msg_pdbg("%ld myus = %ld us, ", resolution * 4, timeusec);

	msg_pinfo("OK.\n");
}

/* Not very precise sleep. */
void internal_sleep(unsigned int usecs)
{
#if IS_WINDOWS
	Sleep((usecs + 999) / 1000);
#elif defined(__DJGPP__)
	sleep(usecs / 1000000);
	usleep(usecs % 1000000);
#else
	nanosleep(&(struct timespec){usecs / 1000000, (usecs * 1000) % 1000000000UL}, NULL);
#endif
}

/* Precise delay. */
void internal_delay(unsigned int usecs)
{
	/* If the delay is >1 s, use internal_sleep because timing does not need to be so precise. */
	if (usecs > 1000000) {
		internal_sleep(usecs);
	} else if (use_clock_gettime) {
		clock_usec_delay(usecs);
	} else {
		myusec_delay(usecs);
	}
}

#else
#include <libpayload.h>

void myusec_calibrate_delay(void)
{
	get_cpu_speed();
}

void internal_delay(unsigned int usecs)
{
	udelay(usecs);
}
#endif