LXR linux/include/linux/delay.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _LINUX_DELAY_H
   3#define _LINUX_DELAY_H
   4
   5/*
   6 * Copyright (C) 1993 Linus Torvalds
   7 *
   8 * Delay routines, using a pre-computed "loops_per_jiffy" value.
   9 *
  10 * Please note that ndelay(), udelay() and mdelay() may return early for
  11 * several reasons:
  12 *  1. computed loops_per_jiffy too low (due to the time taken to
  13 *     execute the timer interrupt.)
  14 *  2. cache behaviour affecting the time it takes to execute the
  15 *     loop function.
  16 *  3. CPU clock rate changes.
  17 *
  18 * Please see this thread:
  19 *   https://lists.openwall.net/linux-kernel/2011/01/09/56
  20 */
  21
  22#include <linux/kernel.h>
  23
  24extern unsigned long loops_per_jiffy;
  25
  26#include <asm/delay.h>
  27
  28/*
  29 * Using udelay() for intervals greater than a few milliseconds can
  30 * risk overflow for high loops_per_jiffy (high bogomips) machines. The
  31 * mdelay() provides a wrapper to prevent this.  For delays greater
  32 * than MAX_UDELAY_MS milliseconds, the wrapper is used.  Architecture
  33 * specific values can be defined in asm-???/delay.h as an override.
  34 * The 2nd mdelay() definition ensures GCC will optimize away the 
  35 * while loop for the common cases where n <= MAX_UDELAY_MS  --  Paul G.
  36 */
  37
  38#ifndef MAX_UDELAY_MS
  39#define MAX_UDELAY_MS   5
  40#endif
  41
  42#ifndef mdelay
  43#define mdelay(n) (\
  44        (__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
  45        ({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
  46#endif
  47
  48#ifndef ndelay
  49static inline void ndelay(unsigned long x)
  50{
  51        udelay(DIV_ROUND_UP(x, 1000));
  52}
  53#define ndelay(x) ndelay(x)
  54#endif
  55
  56extern unsigned long lpj_fine;
  57void calibrate_delay(void);
  58void __attribute__((weak)) calibration_delay_done(void);
  59void msleep(unsigned int msecs);
  60unsigned long msleep_interruptible(unsigned int msecs);
  61void usleep_range(unsigned long min, unsigned long max);
  62
  63static inline void ssleep(unsigned int seconds)
  64{
  65        msleep(seconds * 1000);
  66}
  67
  68/* see Documentation/timers/timers-howto.rst for the thresholds */
  69static inline void fsleep(unsigned long usecs)
  70{
  71        if (usecs <= 10)
  72                udelay(usecs);
  73        else if (usecs <= 20000)
  74                usleep_range(usecs, 2 * usecs);
  75        else
  76                msleep(DIV_ROUND_UP(usecs, 1000));
  77}
  78
  79#endif /* defined(_LINUX_DELAY_H) */
  80