tty-ldisc: get rid of tty_ldisc_try_get() helper function
[linux-2.6/mini2440.git] / init / calibrate.c
bloba379c9061199c64368936a88f91353992a4d5f92
1 /* calibrate.c: default delay calibration
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
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>
13 unsigned long lpj_fine;
14 unsigned long preset_lpj;
15 static int __init lpj_setup(char *str)
17 preset_lpj = simple_strtoul(str,NULL,0);
18 return 1;
21 __setup("lpj=", lpj_setup);
23 #ifdef ARCH_HAS_READ_CURRENT_TIMER
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)
30 #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
31 #define MAX_DIRECT_CALIBRATION_RETRIES 5
33 static unsigned long __cpuinit calibrate_delay_direct(void)
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;
43 if (read_current_timer(&pre_start) < 0 )
44 return 0;
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.
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
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
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);
73 read_current_timer(&post_start);
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);
82 read_current_timer(&post_end);
84 timer_rate_max = (post_end - pre_start) /
85 DELAY_CALIBRATION_TICKS;
86 timer_rate_min = (pre_end - post_start) /
87 DELAY_CALIBRATION_TICKS;
90 * If the upper limit and lower limit of the timer_rate is
91 * >= 12.5% apart, redo calibration.
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;
100 if (good_timer_count)
101 return (good_timer_sum/good_timer_count);
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;
107 #else
108 static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
109 #endif
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.
120 #define LPS_PREC 8
122 void __cpuinit calibrate_delay(void)
124 unsigned long ticks, loopbit;
125 int lps_precision = LPS_PREC;
127 if (preset_lpj) {
128 loops_per_jiffy = preset_lpj;
129 printk(KERN_INFO
130 "Calibrating delay loop (skipped) preset value.. ");
131 } else if ((smp_processor_id() == 0) && lpj_fine) {
132 loops_per_jiffy = lpj_fine;
133 printk(KERN_INFO
134 "Calibrating delay loop (skipped), "
135 "value calculated using timer frequency.. ");
136 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
137 printk(KERN_INFO
138 "Calibrating delay using timer specific routine.. ");
139 } else {
140 loops_per_jiffy = (1<<12);
142 printk(KERN_INFO "Calibrating delay loop... ");
143 while ((loops_per_jiffy <<= 1) != 0) {
144 /* wait for "start of" clock tick */
145 ticks = jiffies;
146 while (ticks == jiffies)
147 /* nothing */;
148 /* Go .. */
149 ticks = jiffies;
150 __delay(loops_per_jiffy);
151 ticks = jiffies - ticks;
152 if (ticks)
153 break;
157 * Do a binary approximation to get loops_per_jiffy set to
158 * equal one clock (up to lps_precision bits)
160 loops_per_jiffy >>= 1;
161 loopbit = loops_per_jiffy;
162 while (lps_precision-- && (loopbit >>= 1)) {
163 loops_per_jiffy |= loopbit;
164 ticks = jiffies;
165 while (ticks == jiffies)
166 /* nothing */;
167 ticks = jiffies;
168 __delay(loops_per_jiffy);
169 if (jiffies != ticks) /* longer than 1 tick */
170 loops_per_jiffy &= ~loopbit;
173 printk(KERN_CONT "%lu.%02lu BogoMIPS (lpj=%lu)\n",
174 loops_per_jiffy/(500000/HZ),
175 (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);