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         register unsigned long r0 __asm__("$0") = loops;
  16 #ifdef MODULE
  17         __asm__ __volatile__("lda $28,___delay; jsr $28,($28),0"
  18                              : "=r"(r0) : "r"(r0) : "$28");
  19 #else
  20         __asm__ __volatile__("bsr $28,___delay" : "=r"(r0) : "r"(r0) : "$28");
  21 #endif
  22 }
  23
  24 /*
  25  * division by multiplication: you don't have to worry about
  26  * loss of precision.
  27  *
  28  * Use only for very small delays ( < 1 msec).  Should probably use a
  29  * lookup table, really, as the multiplications take much too long with
  30  * short delays.  This is a "reasonable" implementation, though (and the
  31  * first constant multiplications gets optimized away if the delay is
  32  * a constant).
  33  *
  34  * Optimize small constants further by exposing the second multiplication
  35  * to the compiler.  In addition, mulq is 2 cycles faster than umulh.
  36  */
  37
  38 extern __inline__ void
  39 __udelay(unsigned long usecs, unsigned long lps)
  40 {
  41         /* compute (usecs * 2**64 / 10**6) * loops_per_sec / 2**64 */
  42
  43         usecs *= 0x000010c6f7a0b5edUL;          /* 2**64 / 1000000 */
  44         __asm__("umulh %1,%2,%0" :"=r" (usecs) :"r" (usecs),"r" (lps));
  45         __delay(usecs);
  46 }
  47
  48 extern __inline__ void
  49 __small_const_udelay(unsigned long usecs, unsigned long lps)
  50 {
  51         /* compute (usecs * 2**32 / 10**6) * loops_per_sec / 2**32 */
  52
  53         usecs *= 0x10c6;                /* 2^32 / 10^6 */
  54         usecs *= lps;
  55         usecs >>= 32;
  56         __delay(usecs);
  57 }
  58
  59 #ifdef __SMP__
  60 #define udelay(usecs)                                           \
  61         (__builtin_constant_p(usecs) && usecs < 0x100000000UL   \
  62          ? __small_const_udelay(usecs,                          \
  63                 cpu_data[smp_processor_id()].loops_per_sec)     \
  64          : __udelay(usecs,                                      \
  65                 cpu_data[smp_processor_id()].loops_per_sec))
  66 #else
  67 #define udelay(usecs)                                           \
  68         (__builtin_constant_p(usecs) && usecs < 0x100000000UL   \
  69          ? __small_const_udelay(usecs, loops_per_sec)           \
  70          : __udelay(usecs, loops_per_sec))
  71 #endif
  72
  73
  74 #endif /* defined(__ALPHA_DELAY_H) */