tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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: */
30static 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: */
51static void delay_tsc(unsigned long loops)
52{
53 unsigned long bclock, now;
54 int cpu;
55
56 preempt_disable();
57 cpu = smp_processor_id();
58 rdtscl(bclock);
59 for (;;) {
60 rdtscl(now);
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 rdtscl(bclock);
82 }
83 }
84 preempt_enable();
85}
86
87/*
88 * Since we calibrate only once at boot, this
89 * function should be set once at boot and not changed
90 */
91static void (*delay_fn)(unsigned long) = delay_loop;
92
93void use_tsc_delay(void)
94{
95 delay_fn = delay_tsc;
96}
97
98int __devinit read_current_timer(unsigned long *timer_val)
99{
100 if (delay_fn == delay_tsc) {
101 rdtscll(*timer_val);
102 return 0;
103 }
104 return -1;
105}
106
107void __delay(unsigned long loops)
108{
109 delay_fn(loops);
110}
111EXPORT_SYMBOL(__delay);
112
113inline void __const_udelay(unsigned long xloops)
114{
115 int d0;
116
117 xloops *= 4;
118 asm("mull %%edx"
119 :"=d" (xloops), "=&a" (d0)
120 :"1" (xloops), "0"
121 (cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4)));
122
123 __delay(++xloops);
124}
125EXPORT_SYMBOL(__const_udelay);
126
127void __udelay(unsigned long usecs)
128{
129 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
130}
131EXPORT_SYMBOL(__udelay);
132
133void __ndelay(unsigned long nsecs)
134{
135 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
136}
137EXPORT_SYMBOL(__ndelay);