1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Precise Delay Loops for i386 4 * 5 * Copyright (C) 1993 Linus Torvalds 6 * Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz> 7 * Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com> 8 * 9 * The __delay function must _NOT_ be inlined as its execution time 10 * depends wildly on alignment on many x86 processors. The additional 11 * jump magic is needed to get the timing stable on all the CPU's 12 * we have to worry about. 13 */ 14 15 #include <linux/export.h> 16 #include <linux/sched.h> 17 #include <linux/timex.h> 18 #include <linux/preempt.h> 19 #include <linux/delay.h> 20 21 #include <asm/processor.h> 22 #include <asm/delay.h> 23 #include <asm/timer.h> 24 #include <asm/mwait.h> 25 26 #ifdef CONFIG_SMP 27 # include <asm/smp.h> 28 #endif 29 30 /* simple loop based delay: */ 31 static void delay_loop(unsigned long loops) 32 { 33 asm volatile( 34 " test %0,%0 \n" 35 " jz 3f \n" 36 " jmp 1f \n" 37 38 ".align 16 \n" 39 "1: jmp 2f \n" 40 41 ".align 16 \n" 42 "2: dec %0 \n" 43 " jnz 2b \n" 44 "3: dec %0 \n" 45 46 : /* we don't need output */ 47 :"a" (loops) 48 ); 49 } 50 51 /* TSC based delay: */ 52 static void delay_tsc(unsigned long __loops) 53 { 54 u64 bclock, now, loops = __loops; 55 int cpu; 56 57 preempt_disable(); 58 cpu = smp_processor_id(); 59 bclock = rdtsc_ordered(); 60 for (;;) { 61 now = rdtsc_ordered(); 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 bclock = rdtsc_ordered(); 83 } 84 } 85 preempt_enable(); 86 } 87 88 /* 89 * On some AMD platforms, MWAITX has a configurable 32-bit timer, that 90 * counts with TSC frequency. The input value is the loop of the 91 * counter, it will exit when the timer expires. 92 */ 93 static void delay_mwaitx(unsigned long __loops) 94 { 95 u64 start, end, delay, loops = __loops; 96 97 /* 98 * Timer value of 0 causes MWAITX to wait indefinitely, unless there 99 * is a store on the memory monitored by MONITORX. 100 */ 101 if (loops == 0) 102 return; 103 104 start = rdtsc_ordered(); 105 106 for (;;) { 107 delay = min_t(u64, MWAITX_MAX_LOOPS, loops); 108 109 /* 110 * Use cpu_tss_rw as a cacheline-aligned, seldomly 111 * accessed per-cpu variable as the monitor target. 112 */ 113 __monitorx(raw_cpu_ptr(&cpu_tss_rw), 0, 0); 114 115 /* 116 * AMD, like Intel, supports the EAX hint and EAX=0xf 117 * means, do not enter any deep C-state and we use it 118 * here in delay() to minimize wakeup latency. 119 */ 120 __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE); 121 122 end = rdtsc_ordered(); 123 124 if (loops <= end - start) 125 break; 126 127 loops -= end - start; 128 129 start = end; 130 } 131 } 132 133 /* 134 * Since we calibrate only once at boot, this 135 * function should be set once at boot and not changed 136 */ 137 static void (*delay_fn)(unsigned long) = delay_loop; 138 139 void use_tsc_delay(void) 140 { 141 if (delay_fn == delay_loop) 142 delay_fn = delay_tsc; 143 } 144 145 void use_mwaitx_delay(void) 146 { 147 delay_fn = delay_mwaitx; 148 } 149 150 int read_current_timer(unsigned long *timer_val) 151 { 152 if (delay_fn == delay_tsc) { 153 *timer_val = rdtsc(); 154 return 0; 155 } 156 return -1; 157 } 158 159 void __delay(unsigned long loops) 160 { 161 delay_fn(loops); 162 } 163 EXPORT_SYMBOL(__delay); 164 165 void __const_udelay(unsigned long xloops) 166 { 167 unsigned long lpj = this_cpu_read(cpu_info.loops_per_jiffy) ? : loops_per_jiffy; 168 int d0; 169 170 xloops *= 4; 171 asm("mull %%edx" 172 :"=d" (xloops), "=&a" (d0) 173 :"1" (xloops), "0" (lpj * (HZ / 4))); 174 175 __delay(++xloops); 176 } 177 EXPORT_SYMBOL(__const_udelay); 178 179 void __udelay(unsigned long usecs) 180 { 181 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */ 182 } 183 EXPORT_SYMBOL(__udelay); 184 185 void __ndelay(unsigned long nsecs) 186 { 187 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */ 188 } 189 EXPORT_SYMBOL(__ndelay); 190