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
11#include <asm/timex.h>
12
13static unsigned long preset_lpj;
14static int __init lpj_setup(char *str)
15{
16	preset_lpj = simple_strtoul(str,NULL,0);
17	return 1;
18}
19
20__setup("lpj=", lpj_setup);
21
22#ifdef ARCH_HAS_READ_CURRENT_TIMER
23
24/* This routine uses the read_current_timer() routine and gets the
25 * loops per jiffy directly, instead of guessing it using delay().
26 * Also, this code tries to handle non-maskable asynchronous events
27 * (like SMIs)
28 */
29#define DELAY_CALIBRATION_TICKS			((HZ < 100) ? 1 : (HZ/100))
30#define MAX_DIRECT_CALIBRATION_RETRIES		5
31
32static unsigned long __devinit calibrate_delay_direct(void)
33{
34	unsigned long pre_start, start, post_start;
35	unsigned long pre_end, end, post_end;
36	unsigned long start_jiffies;
37	unsigned long tsc_rate_min, tsc_rate_max;
38	unsigned long good_tsc_sum = 0;
39	unsigned long good_tsc_count = 0;
40	int i;
41
42	if (read_current_timer(&pre_start) < 0 )
43		return 0;
44
45	/*
46	 * A simple loop like
47	 *	while ( jiffies < start_jiffies+1)
48	 *		start = read_current_timer();
49	 * will not do. As we don't really know whether jiffy switch
50	 * happened first or timer_value was read first. And some asynchronous
51	 * event can happen between these two events introducing errors in lpj.
52	 *
53	 * So, we do
54	 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
55	 * 2. check jiffy switch
56	 * 3. start <- timer value before or after jiffy switch
57	 * 4. post_start <- When we are sure that jiffy switch has happened
58	 *
59	 * Note, we don't know anything about order of 2 and 3.
60	 * Now, by looking at post_start and pre_start difference, we can
61	 * check whether any asynchronous event happened or not
62	 */
63
64	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
65		pre_start = 0;
66		read_current_timer(&start);
67		start_jiffies = jiffies;
68		while (jiffies <= (start_jiffies + 1)) {
69			pre_start = start;
70			read_current_timer(&start);
71		}
72		read_current_timer(&post_start);
73
74		pre_end = 0;
75		end = post_start;
76		while (jiffies <=
77		       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
78			pre_end = end;
79			read_current_timer(&end);
80		}
81		read_current_timer(&post_end);
82
83		tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
84		tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
85
86		/*
87	 	 * If the upper limit and lower limit of the tsc_rate is
88		 * >= 12.5% apart, redo calibration.
89		 */
90		if (pre_start != 0 && pre_end != 0 &&
91		    (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
92			good_tsc_count++;
93			good_tsc_sum += tsc_rate_max;
94		}
95	}
96
97	if (good_tsc_count)
98		return (good_tsc_sum/good_tsc_count);
99
100	printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
101	       "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
102	return 0;
103}
104#else
105static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
106#endif
107
108#if defined(CONFIG_BCM947XX) && defined(CONFIG_HWSIM)
109#include <asm/time.h>
110#endif
111
112/*
113 * This is the number of bits of precision for the loops_per_jiffy.  Each
114 * bit takes on average 1.5/HZ seconds.  This (like the original) is a little
115 * better than 1%
116 */
117#define LPS_PREC 8
118
119void __devinit calibrate_delay(void)
120{
121	unsigned long ticks, loopbit;
122	int lps_precision = LPS_PREC;
123
124#if defined(CONFIG_BCM947XX) && defined(CONFIG_HWSIM)
125	preset_lpj = 10 * (mips_hpt_frequency / 1000);
126#endif
127	if (preset_lpj) {
128		loops_per_jiffy = preset_lpj;
129		printk("Calibrating delay loop (skipped)... "
130			"%lu.%02lu BogoMIPS preset\n",
131			loops_per_jiffy/(500000/HZ),
132			(loops_per_jiffy/(5000/HZ)) % 100);
133	} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
134		printk("Calibrating delay using timer specific routine.. ");
135		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
136			loops_per_jiffy/(500000/HZ),
137			(loops_per_jiffy/(5000/HZ)) % 100,
138			loops_per_jiffy);
139	} else {
140		loops_per_jiffy = (1<<12);
141
142		printk(KERN_DEBUG "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;
154		}
155
156		/*
157		 * Do a binary approximation to get loops_per_jiffy set to
158		 * equal one clock (up to lps_precision bits)
159		 */
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;
171		}
172
173		/* Round the value and print it */
174		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
175			loops_per_jiffy/(500000/HZ),
176			(loops_per_jiffy/(5000/HZ)) % 100,
177			loops_per_jiffy);
178	}
179
180}
181