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/module.h>
  14 #include <linux/sched.h>
  15 #include <linux/delay.h>
  16
  17 #include <asm/processor.h>
  18 #include <asm/delay.h>
  19 #include <asm/timer.h>
  20
  21 #ifdef CONFIG_SMP
  22 # include <asm/smp.h>
  23 #endif
  24
  25 /* simple loop based delay: */
  26 static void delay_loop(unsigned long loops)
  27 {
  28         int d0;
  29
  30         __asm__ __volatile__(
  31                 "\tjmp 1f\n"
  32                 ".align 16\n"
  33                 "1:\tjmp 2f\n"
  34                 ".align 16\n"
  35                 "2:\tdecl %0\n\tjns 2b"
  36                 :"=&a" (d0)
  37                 :"0" (loops));
  38 }
  39
  40 /* TSC based delay: */
  41 static void delay_tsc(unsigned long loops)
  42 {
  43         unsigned long bclock, now;
  44
  45         rdtscl(bclock);
  46         do {
  47                 rep_nop();
  48                 rdtscl(now);
  49         } while ((now-bclock) < loops);
  50 }
  51
  52 /*
  53  * Since we calibrate only once at boot, this
  54  * function should be set once at boot and not changed
  55  */
  56 static void (*delay_fn)(unsigned long) = delay_loop;
  57
  58 void use_tsc_delay(void)
  59 {
  60         delay_fn = delay_tsc;
  61 }
  62
  63 int read_current_timer(unsigned long *timer_val)
  64 {
  65         if (delay_fn == delay_tsc) {
  66                 rdtscl(*timer_val);
  67                 return 0;
  68         }
  69         return -1;
  70 }
  71
  72 void __delay(unsigned long loops)
  73 {
  74         delay_fn(loops);
  75 }
  76
  77 inline void __const_udelay(unsigned long xloops)
  78 {
  79         int d0;
  80
  81         xloops *= 4;
  82         __asm__("mull %0"
  83                 :"=d" (xloops), "=&a" (d0)
  84                 :"1" (xloops), "0"
  85                 (cpu_data[raw_smp_processor_id()].loops_per_jiffy * (HZ/4)));
  86
  87         __delay(++xloops);
  88 }
  89
  90 void __udelay(unsigned long usecs)
  91 {
  92         __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
  93 }
  94
  95 void __ndelay(unsigned long nsecs)
  96 {
  97         __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
  98 }
  99
 100 EXPORT_SYMBOL(__delay);
 101 EXPORT_SYMBOL(__const_udelay);
 102 EXPORT_SYMBOL(__udelay);
 103 EXPORT_SYMBOL(__ndelay);