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/export.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); 182