linux/include/linux/delay.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_DELAY_H
#define _LINUX_DELAY_H

/*
 * Copyright (C) 1993 Linus Torvalds
 *
 * Delay routines, using a pre-computed "loops_per_jiffy" value.
 *
 * Please note that ndelay(), udelay() and mdelay() may return early for
 * several reasons:
 *  1. computed loops_per_jiffy too low (due to the time taken to
 *     execute the timer interrupt.)
 *  2. cache behaviour affecting the time it takes to execute the
 *     loop function.
 *  3. CPU clock rate changes.
 *
 * Please see this thread:
 *   https://lists.openwall.net/linux-kernel/2011/01/09/56
 */

#include <linux/math.h>
#include <linux/sched.h>

extern unsigned long loops_per_jiffy;

#include <asm/delay.h>

/*
 * Using udelay() for intervals greater than a few milliseconds can
 * risk overflow for high loops_per_jiffy (high bogomips) machines. The
 * mdelay() provides a wrapper to prevent this.  For delays greater
 * than MAX_UDELAY_MS milliseconds, the wrapper is used.  Architecture
 * specific values can be defined in asm-???/delay.h as an override.
 * The 2nd mdelay() definition ensures GCC will optimize away the 
 * while loop for the common cases where n <= MAX_UDELAY_MS  --  Paul G.
 */

#ifndef MAX_UDELAY_MS
#define MAX_UDELAY_MS …
#endif

#ifndef mdelay
#define mdelay(n) …
#endif

#ifndef ndelay
static inline void ndelay(unsigned long x)
{
	udelay(DIV_ROUND_UP(x, 1000));
}
#define ndelay …
#endif

extern unsigned long lpj_fine;
void calibrate_delay(void);
unsigned long calibrate_delay_is_known(void);
void __attribute__((weak)) calibration_delay_done(void);
void msleep(unsigned int msecs);
unsigned long msleep_interruptible(unsigned int msecs);
void usleep_range_state(unsigned long min, unsigned long max,
			unsigned int state);

static inline void usleep_range(unsigned long min, unsigned long max)
{ … }

static inline void usleep_idle_range(unsigned long min, unsigned long max)
{ … }

static inline void ssleep(unsigned int seconds)
{ … }

/* see Documentation/timers/timers-howto.rst for the thresholds */
static inline void fsleep(unsigned long usecs)
{ … }

#endif /* defined(_LINUX_DELAY_H) */