include/asm-ppc/delay.h

   1 #ifdef __KERNEL__
   2 #ifndef _PPC_DELAY_H
   3 #define _PPC_DELAY_H
   4
   5 #include <asm/param.h>
   6
   7 /*
   8  * Copyright 1996, Paul Mackerras.
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * as published by the Free Software Foundation; either version
  13  * 2 of the License, or (at your option) any later version.
  14  */
  15
  16 extern unsigned long loops_per_jiffy;
  17
  18 extern void __delay(unsigned int loops);
  19
  20 /*
  21  * Note that 19 * 226 == 4294 ==~ 2^32 / 10^6, so
  22  * loops = (4294 * usecs * loops_per_jiffy * HZ) / 2^32.
  23  *
  24  * The mulhwu instruction gives us loops = (a * b) / 2^32.
  25  * We choose a = usecs * 19 * HZ and b = loops_per_jiffy * 226
  26  * because this lets us support a wide range of HZ and
  27  * loops_per_jiffy values without either a or b overflowing 2^32.
  28  * Thus we need usecs * HZ <= (2^32 - 1) / 19 = 226050910 and
  29  * loops_per_jiffy <= (2^32 - 1) / 226 = 19004280
  30  * (which corresponds to ~3800 bogomips at HZ = 100).
  31  *  -- paulus
  32  */
  33 #define __MAX_UDELAY    (226050910UL/HZ)        /* maximum udelay argument */
  34 #define __MAX_NDELAY    (4294967295UL/HZ)       /* maximum ndelay argument */
  35
  36 extern __inline__ void __udelay(unsigned int x)
  37 {
  38         unsigned int loops;
  39
  40         __asm__("mulhwu %0,%1,%2" : "=r" (loops) :
  41                 "r" (x), "r" (loops_per_jiffy * 226));
  42         __delay(loops);
  43 }
  44
  45 extern __inline__ void __ndelay(unsigned int x)
  46 {
  47         unsigned int loops;
  48
  49         __asm__("mulhwu %0,%1,%2" : "=r" (loops) :
  50                 "r" (x), "r" (loops_per_jiffy * 5));
  51         __delay(loops);
  52 }
  53
  54 extern void __bad_udelay(void);         /* deliberately undefined */
  55 extern void __bad_ndelay(void);         /* deliberately undefined */
  56
  57 #define udelay(n) (__builtin_constant_p(n)? \
  58         ((n) > __MAX_UDELAY? __bad_udelay(): __udelay((n) * (19 * HZ))) : \
  59         __udelay((n) * (19 * HZ)))
  60
  61 #define ndelay(n) (__builtin_constant_p(n)? \
  62         ((n) > __MAX_NDELAY? __bad_ndelay(): __ndelay((n) * HZ)) : \
  63         __ndelay((n) * HZ))
  64
  65 #endif /* defined(_PPC_DELAY_H) */
  66 #endif /* __KERNEL__ */