arch/x86/lib/delay_32.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/timex.h>
  16 #include <linux/preempt.h>
  17 #include <linux/delay.h>
  18 #include <linux/init.h>
  19
  20 #include <asm/processor.h>
  21 #include <asm/delay.h>
  22 #include <asm/timer.h>
  23
  24 #ifdef CONFIG_SMP
  25 # include <asm/smp.h>
  26 #endif
  27
  28 /* simple loop based delay: */
  29 static void delay_loop(unsigned long loops)
  30 {
  31         int d0;
  32
  33         __asm__ __volatile__(
  34                 "\tjmp 1f\n"
  35                 ".align 16\n"
  36                 "1:\tjmp 2f\n"
  37                 ".align 16\n"
  38                 "2:\tdecl %0\n\tjns 2b"
  39                 :"=&a" (d0)
  40                 :"0" (loops));
  41 }
  42
  43 /* TSC based delay: */
  44 static void delay_tsc(unsigned long loops)
  45 {
  46         unsigned long bclock, now;
  47
  48         preempt_disable();              /* TSC's are per-cpu */
  49         rdtscl(bclock);
  50         do {
  51                 rep_nop();
  52                 rdtscl(now);
  53         } while ((now-bclock) < loops);
  54         preempt_enable();
  55 }
  56
  57 /*
  58  * Since we calibrate only once at boot, this
  59  * function should be set once at boot and not changed
  60  */
  61 static void (*delay_fn)(unsigned long) = delay_loop;
  62
  63 void use_tsc_delay(void)
  64 {
  65         delay_fn = delay_tsc;
  66 }
  67
  68 int __devinit read_current_timer(unsigned long *timer_val)
  69 {
  70         if (delay_fn == delay_tsc) {
  71                 rdtscl(*timer_val);
  72                 return 0;
  73         }
  74         return -1;
  75 }
  76
  77 void __delay(unsigned long loops)
  78 {
  79         delay_fn(loops);
  80 }
  81
  82 inline void __const_udelay(unsigned long xloops)
  83 {
  84         int d0;
  85
  86         xloops *= 4;
  87         __asm__("mull %0"
  88                 :"=d" (xloops), "=&a" (d0)
  89                 :"1" (xloops), "0"
  90                 (cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4)));
  91
  92         __delay(++xloops);
  93 }
  94
  95 void __udelay(unsigned long usecs)
  96 {
  97         __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
  98 }
  99
 100 void __ndelay(unsigned long nsecs)
 101 {
 102         __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
 103 }
 104
 105 EXPORT_SYMBOL(__delay);
 106 EXPORT_SYMBOL(__const_udelay);
 107 EXPORT_SYMBOL(__udelay);
 108 EXPORT_SYMBOL(__ndelay);