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Linux/include/linux/delay.h

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  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  *   http://lists.openwall.net/linux-kernel/2011/01/09/56
 20  */
 21 
 22 #include <linux/kernel.h>
 23 
 24 extern 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
 49 static inline void ndelay(unsigned long x)
 50 {
 51         udelay(DIV_ROUND_UP(x, 1000));
 52 }
 53 #define ndelay(x) ndelay(x)
 54 #endif
 55 
 56 extern unsigned long lpj_fine;
 57 void calibrate_delay(void);
 58 void __attribute__((weak)) calibration_delay_done(void);
 59 void msleep(unsigned int msecs);
 60 unsigned long msleep_interruptible(unsigned int msecs);
 61 void usleep_range(unsigned long min, unsigned long max);
 62 
 63 static inline void ssleep(unsigned int seconds)
 64 {
 65         msleep(seconds * 1000);
 66 }
 67 
 68 #endif /* defined(_LINUX_DELAY_H) */
 69 

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