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Linux/include/linux/delay.h

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

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