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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 | ||
7 | #include <linux/jiffies.h> | |
8 | #include <linux/delay.h> | |
9 | #include <linux/init.h> | |
10 | #include <linux/timex.h> | |
11 | #include <linux/smp.h> | |
12 | ||
13 | unsigned long lpj_fine; | |
14 | unsigned long preset_lpj; | |
15 | static int __init lpj_setup(char *str) | |
16 | { | |
17 | preset_lpj = simple_strtoul(str,NULL,0); | |
18 | return 1; | |
19 | } | |
20 | ||
21 | __setup("lpj=", lpj_setup); | |
22 | ||
23 | #ifdef ARCH_HAS_READ_CURRENT_TIMER | |
24 | ||
25 | /* This routine uses the read_current_timer() routine and gets the | |
26 | * loops per jiffy directly, instead of guessing it using delay(). | |
27 | * Also, this code tries to handle non-maskable asynchronous events | |
28 | * (like SMIs) | |
29 | */ | |
30 | #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100)) | |
31 | #define MAX_DIRECT_CALIBRATION_RETRIES 5 | |
32 | ||
33 | static unsigned long __cpuinit calibrate_delay_direct(void) | |
34 | { | |
35 | unsigned long pre_start, start, post_start; | |
36 | unsigned long pre_end, end, post_end; | |
37 | unsigned long start_jiffies; | |
38 | unsigned long timer_rate_min, timer_rate_max; | |
39 | unsigned long good_timer_sum = 0; | |
40 | unsigned long good_timer_count = 0; | |
41 | int i; | |
42 | ||
43 | if (read_current_timer(&pre_start) < 0 ) | |
44 | return 0; | |
45 | ||
46 | /* | |
47 | * A simple loop like | |
48 | * while ( jiffies < start_jiffies+1) | |
49 | * start = read_current_timer(); | |
50 | * will not do. As we don't really know whether jiffy switch | |
51 | * happened first or timer_value was read first. And some asynchronous | |
52 | * event can happen between these two events introducing errors in lpj. | |
53 | * | |
54 | * So, we do | |
55 | * 1. pre_start <- When we are sure that jiffy switch hasn't happened | |
56 | * 2. check jiffy switch | |
57 | * 3. start <- timer value before or after jiffy switch | |
58 | * 4. post_start <- When we are sure that jiffy switch has happened | |
59 | * | |
60 | * Note, we don't know anything about order of 2 and 3. | |
61 | * Now, by looking at post_start and pre_start difference, we can | |
62 | * check whether any asynchronous event happened or not | |
63 | */ | |
64 | ||
65 | for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) { | |
66 | pre_start = 0; | |
67 | read_current_timer(&start); | |
68 | start_jiffies = jiffies; | |
69 | while (jiffies <= (start_jiffies + 1)) { | |
70 | pre_start = start; | |
71 | read_current_timer(&start); | |
72 | } | |
73 | read_current_timer(&post_start); | |
74 | ||
75 | pre_end = 0; | |
76 | end = post_start; | |
77 | while (jiffies <= | |
78 | (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) { | |
79 | pre_end = end; | |
80 | read_current_timer(&end); | |
81 | } | |
82 | read_current_timer(&post_end); | |
83 | ||
84 | timer_rate_max = (post_end - pre_start) / | |
85 | DELAY_CALIBRATION_TICKS; | |
86 | timer_rate_min = (pre_end - post_start) / | |
87 | DELAY_CALIBRATION_TICKS; | |
88 | ||
89 | /* | |
90 | * If the upper limit and lower limit of the timer_rate is | |
91 | * >= 12.5% apart, redo calibration. | |
92 | */ | |
93 | if (pre_start != 0 && pre_end != 0 && | |
94 | (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) { | |
95 | good_timer_count++; | |
96 | good_timer_sum += timer_rate_max; | |
97 | } | |
98 | } | |
99 | ||
100 | if (good_timer_count) | |
101 | return (good_timer_sum/good_timer_count); | |
102 | ||
103 | printk(KERN_WARNING "calibrate_delay_direct() failed to get a good " | |
104 | "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n"); | |
105 | return 0; | |
106 | } | |
107 | #else | |
108 | static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;} | |
109 | #endif | |
110 | ||
111 | /* | |
112 | * This is the number of bits of precision for the loops_per_jiffy. Each | |
113 | * bit takes on average 1.5/HZ seconds. This (like the original) is a little | |
114 | * better than 1% | |
115 | * For the boot cpu we can skip the delay calibration and assign it a value | |
116 | * calculated based on the timer frequency. | |
117 | * For the rest of the CPUs we cannot assume that the timer frequency is same as | |
118 | * the cpu frequency, hence do the calibration for those. | |
119 | */ | |
120 | #define LPS_PREC 8 | |
121 | ||
122 | void __cpuinit calibrate_delay(void) | |
123 | { | |
124 | unsigned long ticks, loopbit; | |
125 | int lps_precision = LPS_PREC; | |
126 | static bool printed; | |
127 | ||
128 | if (preset_lpj) { | |
129 | loops_per_jiffy = preset_lpj; | |
130 | if (!printed) | |
131 | pr_info("Calibrating delay loop (skipped) " | |
132 | "preset value.. "); | |
133 | } else if ((!printed) && lpj_fine) { | |
134 | loops_per_jiffy = lpj_fine; | |
135 | pr_info("Calibrating delay loop (skipped), " | |
136 | "value calculated using timer frequency.. "); | |
137 | } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) { | |
138 | if (!printed) | |
139 | pr_info("Calibrating delay using timer " | |
140 | "specific routine.. "); | |
141 | } else { | |
142 | loops_per_jiffy = (1<<12); | |
143 | ||
144 | if (!printed) | |
145 | pr_info("Calibrating delay loop... "); | |
146 | while ((loops_per_jiffy <<= 1) != 0) { | |
147 | /* wait for "start of" clock tick */ | |
148 | ticks = jiffies; | |
149 | while (ticks == jiffies) | |
150 | /* nothing */; | |
151 | /* Go .. */ | |
152 | ticks = jiffies; | |
153 | __delay(loops_per_jiffy); | |
154 | ticks = jiffies - ticks; | |
155 | if (ticks) | |
156 | break; | |
157 | } | |
158 | ||
159 | /* | |
160 | * Do a binary approximation to get loops_per_jiffy set to | |
161 | * equal one clock (up to lps_precision bits) | |
162 | */ | |
163 | loops_per_jiffy >>= 1; | |
164 | loopbit = loops_per_jiffy; | |
165 | while (lps_precision-- && (loopbit >>= 1)) { | |
166 | loops_per_jiffy |= loopbit; | |
167 | ticks = jiffies; | |
168 | while (ticks == jiffies) | |
169 | /* nothing */; | |
170 | ticks = jiffies; | |
171 | __delay(loops_per_jiffy); | |
172 | if (jiffies != ticks) /* longer than 1 tick */ | |
173 | loops_per_jiffy &= ~loopbit; | |
174 | } | |
175 | } | |
176 | if (!printed) | |
177 | pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n", | |
178 | loops_per_jiffy/(500000/HZ), | |
179 | (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy); | |
180 | ||
181 | printed = true; | |
182 | } |