LXR linux/arch/x86/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 *      Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
   7 *
   8 *      The __delay function must _NOT_ be inlined as its execution time
   9 *      depends wildly on alignment on many x86 processors. The additional
  10 *      jump magic is needed to get the timing stable on all the CPU's
  11 *      we have to worry about.
  12 */
  13
  14#include <linux/module.h>
  15#include <linux/sched.h>
  16#include <linux/timex.h>
  17#include <linux/preempt.h>
  18#include <linux/delay.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: */
  29static void delay_loop(unsigned long loops)
  30{
  31        asm volatile(
  32                "       test %0,%0      \n"
  33                "       jz 3f           \n"
  34                "       jmp 1f          \n"
  35
  36                ".align 16              \n"
  37                "1:     jmp 2f          \n"
  38
  39                ".align 16              \n"
  40                "2:     dec %0          \n"
  41                "       jnz 2b          \n"
  42                "3:     dec %0          \n"
  43
  44                : /* we don't need output */
  45                :"a" (loops)
  46        );
  47}
  48
  49/* TSC based delay: */
  50static void delay_tsc(unsigned long __loops)
  51{
  52        u32 bclock, now, loops = __loops;
  53        int cpu;
  54
  55        preempt_disable();
  56        cpu = smp_processor_id();
  57        rdtsc_barrier();
  58        rdtscl(bclock);
  59        for (;;) {
  60                rdtsc_barrier();
  61                rdtscl(now);
  62                if ((now - bclock) >= loops)
  63                        break;
  64
  65                /* Allow RT tasks to run */
  66                preempt_enable();
  67                rep_nop();
  68                preempt_disable();
  69
  70                /*
  71                 * It is possible that we moved to another CPU, and
  72                 * since TSC's are per-cpu we need to calculate
  73                 * that. The delay must guarantee that we wait "at
  74                 * least" the amount of time. Being moved to another
  75                 * CPU could make the wait longer but we just need to
  76                 * make sure we waited long enough. Rebalance the
  77                 * counter for this CPU.
  78                 */
  79                if (unlikely(cpu != smp_processor_id())) {
  80                        loops -= (now - bclock);
  81                        cpu = smp_processor_id();
  82                        rdtsc_barrier();
  83                        rdtscl(bclock);
  84                }
  85        }
  86        preempt_enable();
  87}
  88
  89/*
  90 * Since we calibrate only once at boot, this
  91 * function should be set once at boot and not changed
  92 */
  93static void (*delay_fn)(unsigned long) = delay_loop;
  94
  95void use_tsc_delay(void)
  96{
  97        delay_fn = delay_tsc;
  98}
  99
 100int read_current_timer(unsigned long *timer_val)
 101{
 102        if (delay_fn == delay_tsc) {
 103                rdtscll(*timer_val);
 104                return 0;
 105        }
 106        return -1;
 107}
 108
 109void __delay(unsigned long loops)
 110{
 111        delay_fn(loops);
 112}
 113EXPORT_SYMBOL(__delay);
 114
 115inline void __const_udelay(unsigned long xloops)
 116{
 117        int d0;
 118
 119        xloops *= 4;
 120        asm("mull %%edx"
 121                :"=d" (xloops), "=&a" (d0)
 122                :"1" (xloops), "0"
 123                (this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));
 124
 125        __delay(++xloops);
 126}
 127EXPORT_SYMBOL(__const_udelay);
 128
 129void __udelay(unsigned long usecs)
 130{
 131        __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
 132}
 133EXPORT_SYMBOL(__udelay);
 134
 135void __ndelay(unsigned long nsecs)
 136{
 137        __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
 138}
 139EXPORT_SYMBOL(__ndelay);
 140