[net-next-2.6.git] / init / calibrate.c

/* calibrate.c: default delay calibration
 *
 * Excised from init/main.c
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/init.h>

#include <asm/timex.h>

static unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
	preset_lpj = simple_strtoul(str,NULL,0);
	return 1;
}

__setup("lpj=", lpj_setup);

#ifdef ARCH_HAS_READ_CURRENT_TIMER

/* This routine uses the read_current_timer() routine and gets the
 * loops per jiffy directly, instead of guessing it using delay().
 * Also, this code tries to handle non-maskable asynchronous events
 * (like SMIs)
 */
#define DELAY_CALIBRATION_TICKS			((HZ < 100) ? 1 : (HZ/100))
#define MAX_DIRECT_CALIBRATION_RETRIES		5

static unsigned long __devinit calibrate_delay_direct(void)
{
	unsigned long pre_start, start, post_start;
	unsigned long pre_end, end, post_end;
	unsigned long start_jiffies;
	unsigned long tsc_rate_min, tsc_rate_max;
	unsigned long good_tsc_sum = 0;
	unsigned long good_tsc_count = 0;
	int i;

	if (read_current_timer(&pre_start) < 0 )
		return 0;

	/*
	 * A simple loop like
	 *	while ( jiffies < start_jiffies+1)
	 *		start = read_current_timer();
	 * will not do. As we don't really know whether jiffy switch
	 * happened first or timer_value was read first. And some asynchronous
	 * event can happen between these two events introducing errors in lpj.
	 *
	 * So, we do
	 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
	 * 2. check jiffy switch
	 * 3. start <- timer value before or after jiffy switch
	 * 4. post_start <- When we are sure that jiffy switch has happened
	 *
	 * Note, we don't know anything about order of 2 and 3.
	 * Now, by looking at post_start and pre_start difference, we can
	 * check whether any asynchronous event happened or not
	 */

	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
		pre_start = 0;
		read_current_timer(&start);
		start_jiffies = jiffies;
		while (jiffies <= (start_jiffies + 1)) {
			pre_start = start;
			read_current_timer(&start);
		}
		read_current_timer(&post_start);

		pre_end = 0;
		end = post_start;
		while (jiffies <=
		       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
			pre_end = end;
			read_current_timer(&end);
		}
		read_current_timer(&post_end);

		tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
		tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;

		/*
	 	 * If the upper limit and lower limit of the tsc_rate is
		 * >= 12.5% apart, redo calibration.
		 */
		if (pre_start != 0 && pre_end != 0 &&
		    (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
			good_tsc_count++;
			good_tsc_sum += tsc_rate_max;
		}
	}

	if (good_tsc_count)
		return (good_tsc_sum/good_tsc_count);

	printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
	       "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
	return 0;
}
#else
static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
#endif

/*
 * This is the number of bits of precision for the loops_per_jiffy.  Each
 * bit takes on average 1.5/HZ seconds.  This (like the original) is a little
 * better than 1%
 */
#define LPS_PREC 8

void __devinit calibrate_delay(void)
{
	unsigned long ticks, loopbit;
	int lps_precision = LPS_PREC;

	if (preset_lpj) {
		loops_per_jiffy = preset_lpj;
		printk("Calibrating delay loop (skipped)... "
			"%lu.%02lu BogoMIPS preset\n",
			loops_per_jiffy/(500000/HZ),
			(loops_per_jiffy/(5000/HZ)) % 100);
	} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
		printk("Calibrating delay using timer specific routine.. ");
		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
			loops_per_jiffy/(500000/HZ),
			(loops_per_jiffy/(5000/HZ)) % 100,
			loops_per_jiffy);
	} else {
		loops_per_jiffy = (1<<12);

		printk(KERN_DEBUG "Calibrating delay loop... ");
		while ((loops_per_jiffy <<= 1) != 0) {
			/* wait for "start of" clock tick */
			ticks = jiffies;
			while (ticks == jiffies)
				/* nothing */;
			/* Go .. */
			ticks = jiffies;
			__delay(loops_per_jiffy);
			ticks = jiffies - ticks;
			if (ticks)
				break;
		}

		/*
		 * Do a binary approximation to get loops_per_jiffy set to
		 * equal one clock (up to lps_precision bits)
		 */
		loops_per_jiffy >>= 1;
		loopbit = loops_per_jiffy;
		while (lps_precision-- && (loopbit >>= 1)) {
			loops_per_jiffy |= loopbit;
			ticks = jiffies;
			while (ticks == jiffies)
				/* nothing */;
			ticks = jiffies;
			__delay(loops_per_jiffy);
			if (jiffies != ticks)	/* longer than 1 tick */
				loops_per_jiffy &= ~loopbit;
		}

		/* Round the value and print it */
		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
			loops_per_jiffy/(500000/HZ),
			(loops_per_jiffy/(5000/HZ)) % 100,
			loops_per_jiffy);
	}

}
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
cd354f1a	7	#include <linux/jiffies.h>
1da177e4 LT	8	#include <linux/delay.h>
	9	#include <linux/init.h>
	10
8a9e1b0f VP	11	#include <asm/timex.h>
8a9e1b0f VP	12
1da177e4 LT	13	static unsigned long preset_lpj;
	14	static 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
8a9e1b0f VP	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
	32	static 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
105	static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
106	#endif
107
1da177e4 LT	108	/*
	109	* This is the number of bits of precision for the loops_per_jiffy. Each
	110	* bit takes on average 1.5/HZ seconds. This (like the original) is a little
	111	* better than 1%
	112	*/
	113	#define LPS_PREC 8
	114
	115	void __devinit calibrate_delay(void)
	116	{
	117	unsigned long ticks, loopbit;
	118	int lps_precision = LPS_PREC;
	119
	120	if (preset_lpj) {
	121	loops_per_jiffy = preset_lpj;
	122	printk("Calibrating delay loop (skipped)... "
	123	"%lu.%02lu BogoMIPS preset\n",
	124	loops_per_jiffy/(500000/HZ),
	125	(loops_per_jiffy/(5000/HZ)) % 100);
8a9e1b0f VP	126	} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
	127	printk("Calibrating delay using timer specific routine.. ");
	128	printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
	129	loops_per_jiffy/(500000/HZ),
	130	(loops_per_jiffy/(5000/HZ)) % 100,
	131	loops_per_jiffy);
1da177e4 LT	132	} else {
	133	loops_per_jiffy = (1<<12);
	134
	135	printk(KERN_DEBUG "Calibrating delay loop... ");
	136	while ((loops_per_jiffy <<= 1) != 0) {
	137	/* wait for "start of" clock tick */
	138	ticks = jiffies;
	139	while (ticks == jiffies)
	140	/* nothing */;
	141	/* Go .. */
	142	ticks = jiffies;
	143	__delay(loops_per_jiffy);
	144	ticks = jiffies - ticks;
	145	if (ticks)
	146	break;
	147	}
	148
	149	/*
	150	* Do a binary approximation to get loops_per_jiffy set to
	151	* equal one clock (up to lps_precision bits)
	152	*/
	153	loops_per_jiffy >>= 1;
	154	loopbit = loops_per_jiffy;
	155	while (lps_precision-- && (loopbit >>= 1)) {
	156	loops_per_jiffy \|= loopbit;
	157	ticks = jiffies;
	158	while (ticks == jiffies)
	159	/* nothing */;
	160	ticks = jiffies;
	161	__delay(loops_per_jiffy);
	162	if (jiffies != ticks) /* longer than 1 tick */
	163	loops_per_jiffy &= ~loopbit;
	164	}
	165
	166	/* Round the value and print it */
	167	printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
	168	loops_per_jiffy/(500000/HZ),
	169	(loops_per_jiffy/(5000/HZ)) % 100,
	170	loops_per_jiffy);
	171	}
	172
	173	}