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/math.h>
  23#include <linux/sched.h>
  24
  25extern unsigned long loops_per_jiffy;
  26
  27#include <asm/delay.h>
  28
  29/*
  30 * Using udelay() for intervals greater than a few milliseconds can
  31 * risk overflow for high loops_per_jiffy (high bogomips) machines. The
  32 * mdelay() provides a wrapper to prevent this.  For delays greater
  33 * than MAX_UDELAY_MS milliseconds, the wrapper is used.  Architecture
  34 * specific values can be defined in asm-???/delay.h as an override.
  35 * The 2nd mdelay() definition ensures GCC will optimize away the 
  36 * while loop for the common cases where n <= MAX_UDELAY_MS  --  Paul G.
  37 */
  38
  39#ifndef MAX_UDELAY_MS
  40#define MAX_UDELAY_MS   5
  41#endif
  42
  43#ifndef mdelay
  44#define mdelay(n) (\
  45        (__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
  46        ({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
  47#endif
  48
  49#ifndef ndelay
  50static inline void ndelay(unsigned long x)
  51{
  52        udelay(DIV_ROUND_UP(x, 1000));
  53}
  54#define ndelay(x) ndelay(x)
  55#endif
  56
  57extern unsigned long lpj_fine;
  58void calibrate_delay(void);
  59void __attribute__((weak)) calibration_delay_done(void);
  60void msleep(unsigned int msecs);
  61unsigned long msleep_interruptible(unsigned int msecs);
  62void usleep_range_state(unsigned long min, unsigned long max,
  63                        unsigned int state);
  64
  65static inline void usleep_range(unsigned long min, unsigned long max)
  66{
  67        usleep_range_state(min, max, TASK_UNINTERRUPTIBLE);
  68}
  69
  70static inline void usleep_idle_range(unsigned long min, unsigned long max)
  71{
  72        usleep_range_state(min, max, TASK_IDLE);
  73}
  74
  75static inline void ssleep(unsigned int seconds)
  76{
  77        msleep(seconds * 1000);
  78}
  79
  80/* see Documentation/timers/timers-howto.rst for the thresholds */
  81static inline void fsleep(unsigned long usecs)
  82{
  83        if (usecs <= 10)
  84                udelay(usecs);
  85        else if (usecs <= 20000)
  86                usleep_range(usecs, 2 * usecs);
  87        else
  88                msleep(DIV_ROUND_UP(usecs, 1000));
  89}
  90
  91#endif /* defined(_LINUX_DELAY_H) */
  92