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
20#include <asm/processor.h>
21#include <asm/delay.h>
22#include <asm/timer.h>
23
24#ifdef CONFIG_SMP
25# include <asm/smp.h>
26#endif
27
28/* simple loop based delay: */
29static void delay_loop(unsigned long loops)
30{
31	asm volatile(
32		"	test %0,%0	\n"
33		"	jz 3f		\n"
34		"	jmp 1f		\n"
35
36		".align 16		\n"
37		"1:	jmp 2f		\n"
38
39		".align 16		\n"
40		"2:	dec %0		\n"
41		"	jnz 2b		\n"
42		"3:	dec %0		\n"
43
44		: /* we don't need output */
45		:"a" (loops)
46	);
47}
48
49/* TSC based delay: */
50static void delay_tsc(unsigned long __loops)
51{
52	u32 bclock, now, loops = __loops;
53	int cpu;
54
55	preempt_disable();
56	cpu = smp_processor_id();
57	rdtsc_barrier();
58	rdtscl(bclock);
59	for (;;) {
60		rdtsc_barrier();
61		rdtscl(now);
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			rdtsc_barrier();
83			rdtscl(bclock);
84		}
85	}
86	preempt_enable();
87}
88
89/*
90 * Since we calibrate only once at boot, this
91 * function should be set once at boot and not changed
92 */
93static void (*delay_fn)(unsigned long) = delay_loop;
94
95void use_tsc_delay(void)
96{
97	delay_fn = delay_tsc;
98}
99
100int read_current_timer(unsigned long *timer_val)
101{
102	if (delay_fn == delay_tsc) {
103		rdtscll(*timer_val);
104		return 0;
105	}
106	return -1;
107}
108
109void __delay(unsigned long loops)
110{
111	delay_fn(loops);
112}
113EXPORT_SYMBOL(__delay);
114
115inline void __const_udelay(unsigned long xloops)
116{
117	int d0;
118
119	xloops *= 4;
120	asm("mull %%edx"
121		:"=d" (xloops), "=&a" (d0)
122		:"1" (xloops), "0"
123		(this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));
124
125	__delay(++xloops);
126}
127EXPORT_SYMBOL(__const_udelay);
128
129void __udelay(unsigned long usecs)
130{
131	__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
132}
133EXPORT_SYMBOL(__udelay);
134
135void __ndelay(unsigned long nsecs)
136{
137	__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
138}
139EXPORT_SYMBOL(__ndelay);
140