arch/i386/lib/delay.c

   1 /*
   2  *      Precise Delay Loops for i386
   3  *
   4  *      Copyright (C) 1993 Linus Torvalds
   5  *      Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   6  *
   7  *      The __delay function must _NOT_ be inlined as its execution time
   8  *      depends wildly on alignment on many x86 processors. The additional
   9  *      jump magic is needed to get the timing stable on all the CPU's
  10  *      we have to worry about.
  11  */
  12
  13 #include <linux/sched.h>
  14 #include <linux/delay.h>
  15 #include <asm/delay.h>
  16
  17 #ifdef __SMP__
  18 #include <asm/smp.h>
  19 #endif
  20
  21 int x86_udelay_tsc = 0;         /* Delay via TSC */
  22
  23
  24 /*
  25  *      Do a udelay using the TSC for any CPU that happens
  26  *      to have one that we trust. This could be optimised to avoid
  27  *      the multiply per loop but its a delay loop so who are we kidding...
  28  */
  29
  30 static void __rdtsc_delay(unsigned long loops)
  31 {
  32         unsigned long bclock, now;
  33
  34         rdtscl(bclock);
  35         do
  36         {
  37                 rdtscl(now);
  38         }
  39         while((now-bclock) < loops);
  40 }
  41
  42 /*
  43  *      Non TSC based delay loop for 386, 486, MediaGX
  44  */
  45
  46 static void __loop_delay(unsigned long loops)
  47 {
  48         int d0;
  49         __asm__ __volatile__(
  50                 "\tjmp 1f\n"
  51                 ".align 16\n"
  52                 "1:\tjmp 2f\n"
  53                 ".align 16\n"
  54                 "2:\tdecl %0\n\tjns 2b"
  55                 :"=&a" (d0)
  56                 :"0" (loops));
  57 }
  58
  59 void __delay(unsigned long loops)
  60 {
  61         if(x86_udelay_tsc)
  62                 __rdtsc_delay(loops);
  63         else
  64                 __loop_delay(loops);
  65 }
  66
  67 inline void __const_udelay(unsigned long xloops)
  68 {
  69         int d0;
  70         __asm__("mull %0"
  71                 :"=d" (xloops), "=&a" (d0)
  72                 :"1" (xloops),"0" (current_cpu_data.loops_per_sec));
  73         __delay(xloops);
  74 }
  75
  76 void __udelay(unsigned long usecs)
  77 {
  78         __const_udelay(usecs * 0x000010c6);  /* 2**32 / 1000000 */
  79 }