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 	u32 bclock, now, loops = __loops;
54 	int cpu;
55 
56 	preempt_disable();
57 	cpu = smp_processor_id();
58 	rdtsc_barrier();
59 	rdtscl(bclock);
60 	for (;;) {
61 		rdtsc_barrier();
62 		rdtscl(now);
63 		if ((now - bclock) >= loops)
64 			break;
65 
66 		/* Allow RT tasks to run */
67 		preempt_enable();
68 		rep_nop();
69 		preempt_disable();
70 
71 		/*
72 		 * It is possible that we moved to another CPU, and
73 		 * since TSC's are per-cpu we need to calculate
74 		 * that. The delay must guarantee that we wait "at
75 		 * least" the amount of time. Being moved to another
76 		 * CPU could make the wait longer but we just need to
77 		 * make sure we waited long enough. Rebalance the
78 		 * counter for this CPU.
79 		 */
80 		if (unlikely(cpu != smp_processor_id())) {
81 			loops -= (now - bclock);
82 			cpu = smp_processor_id();
83 			rdtsc_barrier();
84 			rdtscl(bclock);
85 		}
86 	}
87 	preempt_enable();
88 }
89 
90 /*
91  * Since we calibrate only once at boot, this
92  * function should be set once at boot and not changed
93  */
94 static void (*delay_fn)(unsigned long) = delay_loop;
95 
use_tsc_delay(void)96 void use_tsc_delay(void)
97 {
98 	delay_fn = delay_tsc;
99 }
100 
read_current_timer(unsigned long * timer_val)101 int __devinit read_current_timer(unsigned long *timer_val)
102 {
103 	if (delay_fn == delay_tsc) {
104 		rdtscll(*timer_val);
105 		return 0;
106 	}
107 	return -1;
108 }
109 
__delay(unsigned long loops)110 void __delay(unsigned long loops)
111 {
112 	delay_fn(loops);
113 }
114 EXPORT_SYMBOL(__delay);
115 
__const_udelay(unsigned long xloops)116 inline void __const_udelay(unsigned long xloops)
117 {
118 	int d0;
119 
120 	xloops *= 4;
121 	asm("mull %%edx"
122 		:"=d" (xloops), "=&a" (d0)
123 		:"1" (xloops), "0"
124 		(this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));
125 
126 	__delay(++xloops);
127 }
128 EXPORT_SYMBOL(__const_udelay);
129 
__udelay(unsigned long usecs)130 void __udelay(unsigned long usecs)
131 {
132 	__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
133 }
134 EXPORT_SYMBOL(__udelay);
135 
__ndelay(unsigned long nsecs)136 void __ndelay(unsigned long nsecs)
137 {
138 	__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
139 }
140 EXPORT_SYMBOL(__ndelay);
141