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 /* 97 * Timer value of 0 causes MWAITX to wait indefinitely, unless there 98 * is a store on the memory monitored by MONITORX. 99 */ 100 if (loops == 0) 101 return; 102 103 start = rdtsc_ordered(); 104 105 for (;;) { 106 delay = min_t(u64, MWAITX_MAX_LOOPS, loops); 107 108 /* 109 * Use cpu_tss as a cacheline-aligned, seldomly 110 * accessed per-cpu variable as the monitor target. 111 */ 112 __monitorx(raw_cpu_ptr(&cpu_tss), 0, 0); 113 114 /* 115 * AMD, like Intel, supports the EAX hint and EAX=0xf 116 * means, do not enter any deep C-state and we use it 117 * here in delay() to minimize wakeup latency. 118 */ 119 __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE); 120 121 end = rdtsc_ordered(); 122 123 if (loops <= end - start) 124 break; 125 126 loops -= end - start; 127 128 start = end; 129 } 130 } 131 132 /* 133 * Since we calibrate only once at boot, this 134 * function should be set once at boot and not changed 135 */ 136 static void (*delay_fn)(unsigned long) = delay_loop; 137 138 void use_tsc_delay(void) 139 { 140 if (delay_fn == delay_loop) 141 delay_fn = delay_tsc; 142 } 143 144 void use_mwaitx_delay(void) 145 { 146 delay_fn = delay_mwaitx; 147 } 148 149 int read_current_timer(unsigned long *timer_val) 150 { 151 if (delay_fn == delay_tsc) { 152 *timer_val = rdtsc(); 153 return 0; 154 } 155 return -1; 156 } 157 158 void __delay(unsigned long loops) 159 { 160 delay_fn(loops); 161 } 162 EXPORT_SYMBOL(__delay); 163 164 inline void __const_udelay(unsigned long xloops) 165 { 166 unsigned long lpj = this_cpu_read(cpu_info.loops_per_jiffy) ? : loops_per_jiffy; 167 int d0; 168 169 xloops *= 4; 170 asm("mull %%edx" 171 :"=d" (xloops), "=&a" (d0) 172 :"1" (xloops), "0" (lpj * (HZ / 4))); 173 174 __delay(++xloops); 175 } 176 EXPORT_SYMBOL(__const_udelay); 177 178 void __udelay(unsigned long usecs) 179 { 180 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */ 181 } 182 EXPORT_SYMBOL(__udelay); 183 184 void __ndelay(unsigned long nsecs) 185 { 186 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */ 187 } 188 EXPORT_SYMBOL(__ndelay); 189