include/asm-alpha/delay.h

   1 #ifndef __ALPHA_DELAY_H
   2 #define __ALPHA_DELAY_H
   3
   4 #include <asm/smp.h>
   5
   6 /*
   7  * Copyright (C) 1993 Linus Torvalds
   8  *
   9  * Delay routines, using a pre-computed "loops_per_second" value.
  10  */
  11
  12 extern __inline__ void
  13 __delay(unsigned long loops)
  14 {
  15         __asm__ __volatile__(".align 3\n"
  16                 "1:\tsubq %0,1,%0\n\t"
  17                 "bge %0,1b": "=r" (loops) : "0" (loops));
  18 }
  19
  20 /*
  21  * division by multiplication: you don't have to worry about
  22  * loss of precision.
  23  *
  24  * Use only for very small delays ( < 1 msec).  Should probably use a
  25  * lookup table, really, as the multiplications take much too long with
  26  * short delays.  This is a "reasonable" implementation, though (and the
  27  * first constant multiplications gets optimized away if the delay is
  28  * a constant).
  29  *
  30  * Optimize small constants further by exposing the second multiplication
  31  * to the compiler.  In addition, mulq is 2 cycles faster than umulh.
  32  */
  33
  34 extern __inline__ void
  35 __udelay(unsigned long usecs, unsigned long lps)
  36 {
  37         /* compute (usecs * 2**64 / 10**6) * loops_per_sec / 2**64 */
  38
  39         usecs *= 0x000010c6f7a0b5edUL;          /* 2**64 / 1000000 */
  40         __asm__("umulh %1,%2,%0" :"=r" (usecs) :"r" (usecs),"r" (lps));
  41         __delay(usecs);
  42 }
  43
  44 extern __inline__ void
  45 __small_const_udelay(unsigned long usecs, unsigned long lps)
  46 {
  47         /* compute (usecs * 2**32 / 10**6) * loops_per_sec / 2**32 */
  48
  49         usecs *= 0x10c6;                /* 2^32 / 10^6 */
  50         usecs *= lps;
  51         usecs >>= 32;
  52         __delay(usecs);
  53 }
  54
  55 #ifdef __SMP__
  56 #define udelay(usecs)                                           \
  57         (__builtin_constant_p(usecs) && usecs < 0x100000000UL   \
  58          ? __small_const_udelay(usecs,                          \
  59                 cpu_data[smp_processor_id()].loops_per_sec)     \
  60          : __udelay(usecs,                                      \
  61                 cpu_data[smp_processor_id()].loops_per_sec))
  62 #else
  63 #define udelay(usecs)                                           \
  64         (__builtin_constant_p(usecs) && usecs < 0x100000000UL   \
  65          ? __small_const_udelay(usecs, loops_per_sec)           \
  66          : __udelay(usecs, loops_per_sec))
  67 #endif
  68
  69
  70 #endif /* defined(__ALPHA_DELAY_H) */