tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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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/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: */
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 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 */
92static 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 */
136static void (*delay_fn)(unsigned long) = delay_loop;
137
138void use_tsc_delay(void)
139{
140 if (delay_fn == delay_loop)
141 delay_fn = delay_tsc;
142}
143
144void use_mwaitx_delay(void)
145{
146 delay_fn = delay_mwaitx;
147}
148
149int 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
158void __delay(unsigned long loops)
159{
160 delay_fn(loops);
161}
162EXPORT_SYMBOL(__delay);
163
164inline 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}
176EXPORT_SYMBOL(__const_udelay);
177
178void __udelay(unsigned long usecs)
179{
180 __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
181}
182EXPORT_SYMBOL(__udelay);
183
184void __ndelay(unsigned long nsecs)
185{
186 __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
187}
188EXPORT_SYMBOL(__ndelay);