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#include <linux/init.h>
  20
  21#include <asm/processor.h>
  22#include <asm/delay.h>
  23#include <asm/timer.h>
  24
  25#ifdef CONFIG_SMP
  26# include <asm/smp.h>
  27#endif
  28
  29/* simple loop based delay: */
  30static void delay_loop(unsigned long loops)
  31{
  32        asm volatile(
  33                "       test %0,%0      \n"
  34                "       jz 3f           \n"
  35                "       jmp 1f          \n"
  36
  37                ".align 16              \n"
  38                "1:     jmp 2f          \n"
  39
  40                ".align 16              \n"
  41                "2:     dec %0          \n"
  42                "       jnz 2b          \n"
  43                "3:     dec %0          \n"
  44
  45                : /* we don't need output */
  46                :"a" (loops)
  47        );
  48}
  49
  50/* TSC based delay: */
  51static void delay_tsc(unsigned long __loops)
  52{
  53        u32 bclock, now, loops = __loops;
  54        int cpu;
  55
  56        preempt_disable();
  57        cpu = smp_processor_id();
  58        rdtsc_barrier();
  59        rdtscl(bclock);
  60        for (;;) {
  61                rdtsc_barrier();
  62                rdtscl(now);
  63                if ((now - bclock) >= loops)
  64                        break;
  65
  66                /* Allow RT tasks to run */
  67                preempt_enable();
  68                rep_nop();
  69                preempt_disable();
  70
  71                /*
  72                 * It is possible that we moved to another CPU, and
  73                 * since TSC's are per-cpu we need to calculate
  74                 * that. The delay must guarantee that we wait "at
  75                 * least" the amount of time. Being moved to another
  76                 * CPU could make the wait longer but we just need to
  77                 * make sure we waited long enough. Rebalance the
  78                 * counter for this CPU.
  79                 */
  80                if (unlikely(cpu != smp_processor_id())) {
  81                        loops -= (now - bclock);
  82                        cpu = smp_processor_id();
  83                        rdtsc_barrier();
  84                        rdtscl(bclock);
  85                }
  86        }
  87        preempt_enable();
  88}
  89
  90/*
  91 * Since we calibrate only once at boot, this
  92 * function should be set once at boot and not changed
  93 */
  94static void (*delay_fn)(unsigned long) = delay_loop;
  95
  96void use_tsc_delay(void)
  97{
  98        delay_fn = delay_tsc;
  99}
 100
 101int read_current_timer(unsigned long *timer_val)
 102{
 103        if (delay_fn == delay_tsc) {
 104                rdtscll(*timer_val);
 105                return 0;
 106        }
 107        return -1;
 108}
 109
 110void __delay(unsigned long loops)
 111{
 112        delay_fn(loops);
 113}
 114EXPORT_SYMBOL(__delay);
 115
 116inline void __const_udelay(unsigned long xloops)
 117{
 118        int d0;
 119
 120        xloops *= 4;
 121        asm("mull %%edx"
 122                :"=d" (xloops), "=&a" (d0)
 123                :"1" (xloops), "0"
 124                (this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));
 125
 126        __delay(++xloops);
 127}
 128EXPORT_SYMBOL(__const_udelay);
 129
 130void __udelay(unsigned long usecs)
 131{
 132        __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
 133}
 134EXPORT_SYMBOL(__udelay);
 135
 136void __ndelay(unsigned long nsecs)
 137{
 138        __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
 139}
 140EXPORT_SYMBOL(__ndelay);
 141