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: */ 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 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 */ 94 static void (*delay_fn)(unsigned long) = delay_loop; 95 96 void use_tsc_delay(void) 97 { 98 delay_fn = delay_tsc; 99 } 100 101 int __devinit 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 } 109 110 void __delay(unsigned long loops) 111 { 112 delay_fn(loops); 113 } 114 EXPORT_SYMBOL(__delay); 115 116 inline 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 } 128 EXPORT_SYMBOL(__const_udelay); 129 130 void __udelay(unsigned long usecs) 131 { 132 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */ 133 } 134 EXPORT_SYMBOL(__udelay); 135 136 void __ndelay(unsigned long nsecs) 137 { 138 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */ 139 } 140 EXPORT_SYMBOL(__ndelay); 141