arch/x86/lib/delay_64.c

   1 /*
   2  *      Precise Delay Loops for x86-64
   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.
   9  */
  10
  11 #include <linux/module.h>
  12 #include <linux/sched.h>
  13 #include <linux/timex.h>
  14 #include <linux/preempt.h>
  15 #include <linux/delay.h>
  16 #include <linux/init.h>
  17
  18 #include <asm/delay.h>
  19 #include <asm/msr.h>
  20
  21 #ifdef CONFIG_SMP
  22 #include <asm/smp.h>
  23 #endif
  24
  25 int __devinit read_current_timer(unsigned long *timer_value)
  26 {
  27         rdtscll(*timer_value);
  28         return 0;
  29 }
  30
  31 void __delay(unsigned long loops)
  32 {
  33         unsigned bclock, now;
  34         int cpu;
  35
  36         preempt_disable();
  37         cpu = smp_processor_id();
  38         rdtscl(bclock);
  39         for (;;) {
  40                 rdtscl(now);
  41                 if ((now - bclock) >= loops)
  42                         break;
  43
  44                 /* Allow RT tasks to run */
  45                 preempt_enable();
  46                 rep_nop();
  47                 preempt_disable();
  48
  49                 /*
  50                  * It is possible that we moved to another CPU, and
  51                  * since TSC's are per-cpu we need to calculate
  52                  * that. The delay must guarantee that we wait "at
  53                  * least" the amount of time. Being moved to another
  54                  * CPU could make the wait longer but we just need to
  55                  * make sure we waited long enough. Rebalance the
  56                  * counter for this CPU.
  57                  */
  58                 if (unlikely(cpu != smp_processor_id())) {
  59                         loops -= (now - bclock);
  60                         cpu = smp_processor_id();
  61                         rdtscl(bclock);
  62                 }
  63         }
  64         preempt_enable();
  65 }
  66 EXPORT_SYMBOL(__delay);
  67
  68 inline void __const_udelay(unsigned long xloops)
  69 {
  70         __delay(((xloops * HZ *
  71                 cpu_data(raw_smp_processor_id()).loops_per_jiffy) >> 32) + 1);
  72 }
  73 EXPORT_SYMBOL(__const_udelay);
  74
  75 void __udelay(unsigned long usecs)
  76 {
  77         __const_udelay(usecs * 0x000010c7);  /* 2**32 / 1000000 (rounded up) */
  78 }
  79 EXPORT_SYMBOL(__udelay);
  80
  81 void __ndelay(unsigned long nsecs)
  82 {
  83         __const_udelay(nsecs * 0x00005);  /* 2**32 / 1000000000 (rounded up) */
  84 }
  85 EXPORT_SYMBOL(__ndelay);