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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 | } |
183 |
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