Commit | Line | Data |
---|---|---|
1da177e4 LT |
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/sched.h> | |
8 | #include <linux/delay.h> | |
9 | #include <linux/init.h> | |
10 | ||
11 | static unsigned long preset_lpj; | |
12 | static int __init lpj_setup(char *str) | |
13 | { | |
14 | preset_lpj = simple_strtoul(str,NULL,0); | |
15 | return 1; | |
16 | } | |
17 | ||
18 | __setup("lpj=", lpj_setup); | |
19 | ||
20 | /* | |
21 | * This is the number of bits of precision for the loops_per_jiffy. Each | |
22 | * bit takes on average 1.5/HZ seconds. This (like the original) is a little | |
23 | * better than 1% | |
24 | */ | |
25 | #define LPS_PREC 8 | |
26 | ||
27 | void __devinit calibrate_delay(void) | |
28 | { | |
29 | unsigned long ticks, loopbit; | |
30 | int lps_precision = LPS_PREC; | |
31 | ||
32 | if (preset_lpj) { | |
33 | loops_per_jiffy = preset_lpj; | |
34 | printk("Calibrating delay loop (skipped)... " | |
35 | "%lu.%02lu BogoMIPS preset\n", | |
36 | loops_per_jiffy/(500000/HZ), | |
37 | (loops_per_jiffy/(5000/HZ)) % 100); | |
38 | } else { | |
39 | loops_per_jiffy = (1<<12); | |
40 | ||
41 | printk(KERN_DEBUG "Calibrating delay loop... "); | |
42 | while ((loops_per_jiffy <<= 1) != 0) { | |
43 | /* wait for "start of" clock tick */ | |
44 | ticks = jiffies; | |
45 | while (ticks == jiffies) | |
46 | /* nothing */; | |
47 | /* Go .. */ | |
48 | ticks = jiffies; | |
49 | __delay(loops_per_jiffy); | |
50 | ticks = jiffies - ticks; | |
51 | if (ticks) | |
52 | break; | |
53 | } | |
54 | ||
55 | /* | |
56 | * Do a binary approximation to get loops_per_jiffy set to | |
57 | * equal one clock (up to lps_precision bits) | |
58 | */ | |
59 | loops_per_jiffy >>= 1; | |
60 | loopbit = loops_per_jiffy; | |
61 | while (lps_precision-- && (loopbit >>= 1)) { | |
62 | loops_per_jiffy |= loopbit; | |
63 | ticks = jiffies; | |
64 | while (ticks == jiffies) | |
65 | /* nothing */; | |
66 | ticks = jiffies; | |
67 | __delay(loops_per_jiffy); | |
68 | if (jiffies != ticks) /* longer than 1 tick */ | |
69 | loops_per_jiffy &= ~loopbit; | |
70 | } | |
71 | ||
72 | /* Round the value and print it */ | |
73 | printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", | |
74 | loops_per_jiffy/(500000/HZ), | |
75 | (loops_per_jiffy/(5000/HZ)) % 100, | |
76 | loops_per_jiffy); | |
77 | } | |
78 | ||
79 | } |