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1da177e4
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1/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
cd354f1a 7#include <linux/jiffies.h>
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8#include <linux/delay.h>
9#include <linux/init.h>
941e492b 10#include <linux/timex.h>
8a9e1b0f 11
bfe8df3d 12unsigned long preset_lpj;
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13static int __init lpj_setup(char *str)
14{
15 preset_lpj = simple_strtoul(str,NULL,0);
16 return 1;
17}
18
19__setup("lpj=", lpj_setup);
20
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21#ifdef ARCH_HAS_READ_CURRENT_TIMER
22
23/* This routine uses the read_current_timer() routine and gets the
24 * loops per jiffy directly, instead of guessing it using delay().
25 * Also, this code tries to handle non-maskable asynchronous events
26 * (like SMIs)
27 */
28#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
29#define MAX_DIRECT_CALIBRATION_RETRIES 5
30
31static unsigned long __devinit calibrate_delay_direct(void)
32{
33 unsigned long pre_start, start, post_start;
34 unsigned long pre_end, end, post_end;
35 unsigned long start_jiffies;
36 unsigned long tsc_rate_min, tsc_rate_max;
37 unsigned long good_tsc_sum = 0;
38 unsigned long good_tsc_count = 0;
39 int i;
40
41 if (read_current_timer(&pre_start) < 0 )
42 return 0;
43
44 /*
45 * A simple loop like
46 * while ( jiffies < start_jiffies+1)
47 * start = read_current_timer();
48 * will not do. As we don't really know whether jiffy switch
49 * happened first or timer_value was read first. And some asynchronous
50 * event can happen between these two events introducing errors in lpj.
51 *
52 * So, we do
53 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
54 * 2. check jiffy switch
55 * 3. start <- timer value before or after jiffy switch
56 * 4. post_start <- When we are sure that jiffy switch has happened
57 *
58 * Note, we don't know anything about order of 2 and 3.
59 * Now, by looking at post_start and pre_start difference, we can
60 * check whether any asynchronous event happened or not
61 */
62
63 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
64 pre_start = 0;
65 read_current_timer(&start);
66 start_jiffies = jiffies;
67 while (jiffies <= (start_jiffies + 1)) {
68 pre_start = start;
69 read_current_timer(&start);
70 }
71 read_current_timer(&post_start);
72
73 pre_end = 0;
74 end = post_start;
75 while (jiffies <=
76 (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
77 pre_end = end;
78 read_current_timer(&end);
79 }
80 read_current_timer(&post_end);
81
82 tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
83 tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
84
85 /*
86 * If the upper limit and lower limit of the tsc_rate is
87 * >= 12.5% apart, redo calibration.
88 */
89 if (pre_start != 0 && pre_end != 0 &&
90 (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
91 good_tsc_count++;
92 good_tsc_sum += tsc_rate_max;
93 }
94 }
95
96 if (good_tsc_count)
97 return (good_tsc_sum/good_tsc_count);
98
99 printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
100 "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
101 return 0;
102}
103#else
104static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
105#endif
106
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107/*
108 * This is the number of bits of precision for the loops_per_jiffy. Each
109 * bit takes on average 1.5/HZ seconds. This (like the original) is a little
110 * better than 1%
111 */
112#define LPS_PREC 8
113
114void __devinit calibrate_delay(void)
115{
116 unsigned long ticks, loopbit;
117 int lps_precision = LPS_PREC;
118
119 if (preset_lpj) {
120 loops_per_jiffy = preset_lpj;
121 printk("Calibrating delay loop (skipped)... "
122 "%lu.%02lu BogoMIPS preset\n",
123 loops_per_jiffy/(500000/HZ),
124 (loops_per_jiffy/(5000/HZ)) % 100);
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125 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
126 printk("Calibrating delay using timer specific routine.. ");
127 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
128 loops_per_jiffy/(500000/HZ),
129 (loops_per_jiffy/(5000/HZ)) % 100,
130 loops_per_jiffy);
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131 } else {
132 loops_per_jiffy = (1<<12);
133
134 printk(KERN_DEBUG "Calibrating delay loop... ");
135 while ((loops_per_jiffy <<= 1) != 0) {
136 /* wait for "start of" clock tick */
137 ticks = jiffies;
138 while (ticks == jiffies)
139 /* nothing */;
140 /* Go .. */
141 ticks = jiffies;
142 __delay(loops_per_jiffy);
143 ticks = jiffies - ticks;
144 if (ticks)
145 break;
146 }
147
148 /*
149 * Do a binary approximation to get loops_per_jiffy set to
150 * equal one clock (up to lps_precision bits)
151 */
152 loops_per_jiffy >>= 1;
153 loopbit = loops_per_jiffy;
154 while (lps_precision-- && (loopbit >>= 1)) {
155 loops_per_jiffy |= loopbit;
156 ticks = jiffies;
157 while (ticks == jiffies)
158 /* nothing */;
159 ticks = jiffies;
160 __delay(loops_per_jiffy);
161 if (jiffies != ticks) /* longer than 1 tick */
162 loops_per_jiffy &= ~loopbit;
163 }
164
165 /* Round the value and print it */
166 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
167 loops_per_jiffy/(500000/HZ),
168 (loops_per_jiffy/(5000/HZ)) % 100,
169 loops_per_jiffy);
170 }
171
172}