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