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 #include <asm/mwait.h>
  24
  25 #ifdef CONFIG_SMP
  26 # include <asm/smp.h>
  27 #endif
  28
  29 /* simple loop based delay: */
  30 static 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: */
  51 static void delay_tsc(unsigned long __loops)
  52 {
  53         u64 bclock, now, loops = __loops;
  54         int cpu;
  55
  56         preempt_disable();
  57         cpu = smp_processor_id();
  58         bclock = rdtsc_ordered();
  59         for (;;) {
  60                 now = rdtsc_ordered();
  61                 if ((now - bclock) >= loops)
  62                         break;
  63
  64                 /* Allow RT tasks to run */
  65                 preempt_enable();
  66                 rep_nop();
  67                 preempt_disable();
  68
  69                 /*
  70                  * It is possible that we moved to another CPU, and
  71                  * since TSC's are per-cpu we need to calculate
  72                  * that. The delay must guarantee that we wait "at
  73                  * least" the amount of time. Being moved to another
  74                  * CPU could make the wait longer but we just need to
  75                  * make sure we waited long enough. Rebalance the
  76                  * counter for this CPU.
  77                  */
  78                 if (unlikely(cpu != smp_processor_id())) {
  79                         loops -= (now - bclock);
  80                         cpu = smp_processor_id();
  81                         bclock = rdtsc_ordered();
  82                 }
  83         }
  84         preempt_enable();
  85 }
  86
  87 /*
  88  * On some AMD platforms, MWAITX has a configurable 32-bit timer, that
  89  * counts with TSC frequency. The input value is the loop of the
  90  * counter, it will exit when the timer expires.
  91  */
  92 static void delay_mwaitx(unsigned long __loops)
  93 {
  94         u64 start, end, delay, loops = __loops;
  95
  96         start = rdtsc_ordered();
  97
  98         for (;;) {
  99                 delay = min_t(u64, MWAITX_MAX_LOOPS, loops);
 100
 101                 /*
 102                  * Use cpu_tss as a cacheline-aligned, seldomly
 103                  * accessed per-cpu variable as the monitor target.
 104                  */
 105                 __monitorx(raw_cpu_ptr(&cpu_tss), 0, 0);
 106
 107                 /*
 108                  * AMD, like Intel, supports the EAX hint and EAX=0xf
 109                  * means, do not enter any deep C-state and we use it
 110                  * here in delay() to minimize wakeup latency.
 111                  */
 112                 __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE);
 113
 114                 end = rdtsc_ordered();
 115
 116                 if (loops <= end - start)
 117                         break;
 118
 119                 loops -= end - start;
 120
 121                 start = end;
 122         }
 123 }
 124
 125 /*
 126  * Since we calibrate only once at boot, this
 127  * function should be set once at boot and not changed
 128  */
 129 static void (*delay_fn)(unsigned long) = delay_loop;
 130
 131 void use_tsc_delay(void)
 132 {
 133         if (delay_fn == delay_loop)
 134                 delay_fn = delay_tsc;
 135 }
 136
 137 void use_mwaitx_delay(void)
 138 {
 139         delay_fn = delay_mwaitx;
 140 }
 141
 142 int read_current_timer(unsigned long *timer_val)
 143 {
 144         if (delay_fn == delay_tsc) {
 145                 *timer_val = rdtsc();
 146                 return 0;
 147         }
 148         return -1;
 149 }
 150
 151 void __delay(unsigned long loops)
 152 {
 153         delay_fn(loops);
 154 }
 155 EXPORT_SYMBOL(__delay);
 156
 157 inline void __const_udelay(unsigned long xloops)
 158 {
 159         int d0;
 160
 161         xloops *= 4;
 162         asm("mull %%edx"
 163                 :"=d" (xloops), "=&a" (d0)
 164                 :"1" (xloops), "0"
 165                 (this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));
 166
 167         __delay(++xloops);
 168 }
 169 EXPORT_SYMBOL(__const_udelay);
 170
 171 void __udelay(unsigned long usecs)
 172 {
 173         __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
 174 }
 175 EXPORT_SYMBOL(__udelay);
 176
 177 void __ndelay(unsigned long nsecs)
 178 {
 179         __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
 180 }
 181 EXPORT_SYMBOL(__ndelay);