LXR linux/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: */
  26static 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: */
  41static 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 */
  56static void (*delay_fn)(unsigned long) = delay_loop;
  57
  58void use_tsc_delay(void)
  59{
  60        delay_fn = delay_tsc;
  61}
  62
  63int 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
  72void __delay(unsigned long loops)
  73{
  74        delay_fn(loops);
  75}
  76
  77inline 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
  90void __udelay(unsigned long usecs)
  91{
  92        __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
  93}
  94
  95void __ndelay(unsigned long nsecs)
  96{
  97        __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
  98}
  99
 100EXPORT_SYMBOL(__delay);
 101EXPORT_SYMBOL(__const_udelay);
 102EXPORT_SYMBOL(__udelay);
 103EXPORT_SYMBOL(__ndelay);
 104