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: */ delay_loop(unsigned long loops)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: */ delay_tsc(unsigned long loops)51 static void delay_tsc(unsigned long loops) 52 { 53 unsigned long bclock, now; 54 int cpu; 55 56 preempt_disable(); 57 cpu = smp_processor_id(); 58 rdtscl(bclock); 59 for (;;) { 60 rdtscl(now); 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 rdtscl(bclock); 82 } 83 } 84 preempt_enable(); 85 } 86 87 /* 88 * Since we calibrate only once at boot, this 89 * function should be set once at boot and not changed 90 */ 91 static void (*delay_fn)(unsigned long) = delay_loop; 92 use_tsc_delay(void)93 void use_tsc_delay(void) 94 { 95 delay_fn = delay_tsc; 96 } 97 read_current_timer(unsigned long * timer_val)98 int __devinit read_current_timer(unsigned long *timer_val) 99 { 100 if (delay_fn == delay_tsc) { 101 rdtscll(*timer_val); 102 return 0; 103 } 104 return -1; 105 } 106 __delay(unsigned long loops)107 void __delay(unsigned long loops) 108 { 109 delay_fn(loops); 110 } 111 EXPORT_SYMBOL(__delay); 112 __const_udelay(unsigned long xloops)113 inline void __const_udelay(unsigned long xloops) 114 { 115 int d0; 116 117 xloops *= 4; 118 asm("mull %%edx" 119 :"=d" (xloops), "=&a" (d0) 120 :"1" (xloops), "0" 121 (cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4))); 122 123 __delay(++xloops); 124 } 125 EXPORT_SYMBOL(__const_udelay); 126 __udelay(unsigned long usecs)127 void __udelay(unsigned long usecs) 128 { 129 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */ 130 } 131 EXPORT_SYMBOL(__udelay); 132 __ndelay(unsigned long nsecs)133 void __ndelay(unsigned long nsecs) 134 { 135 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */ 136 } 137 EXPORT_SYMBOL(__ndelay); 138