LXR linux/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
  16extern unsigned long loops_per_jiffy;
  17
  18extern 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
  36extern __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
  45extern __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
  54extern void __bad_udelay(void);         /* deliberately undefined */
  55extern 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__ */
  67