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: */ 29 static 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: */ 50 static 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 */ 93 static void (*delay_fn)(unsigned long) = delay_loop; 94 95 void use_tsc_delay(void) 96 { 97 delay_fn = delay_tsc; 98 } 99 100 int 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 } 108 109 void __delay(unsigned long loops) 110 { 111 delay_fn(loops); 112 } 113 EXPORT_SYMBOL(__delay); 114 115 inline 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 } 127 EXPORT_SYMBOL(__const_udelay); 128 129 void __udelay(unsigned long usecs) 130 { 131 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */ 132 } 133 EXPORT_SYMBOL(__udelay); 134 135 void __ndelay(unsigned long nsecs) 136 { 137 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */ 138 } 139 EXPORT_SYMBOL(__ndelay); 140