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/* 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>

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);

        }

}