ip22-time.c

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/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Time operations for IP22 machines. Original code may come from
 * Ralf Baechle or David S. Miller (sorry guys, i'm really not sure)
 *
 * Copyright (C) 2001 by Ladislav Michl
 * Copyright (C) 2003, 06 Ralf Baechle ([email protected])
 */
#include <linux/bcd.h>
#include <linux/i8253.h>
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/time.h>
#include <linux/ftrace.h>

#include <asm/cpu.h>
#include <asm/mipsregs.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/time.h>
#include <asm/sgialib.h>
#include <asm/sgi/ioc.h>
#include <asm/sgi/hpc3.h>
#include <asm/sgi/ip22.h>

static unsigned long dosample(void)
{
    u32 ct0, ct1;
    u8 msb;

    /* Start the counter. */
    sgint->tcword = (SGINT_TCWORD_CNT2 | SGINT_TCWORD_CALL |
             SGINT_TCWORD_MRGEN);
    sgint->tcnt2 = SGINT_TCSAMP_COUNTER & 0xff;
    sgint->tcnt2 = SGINT_TCSAMP_COUNTER >> 8;

    /* Get initial counter invariant */
    ct0 = read_c0_count();

    /* Latch and spin until top byte of counter2 is zero */
    do {
        writeb(SGINT_TCWORD_CNT2 | SGINT_TCWORD_CLAT, &sgint->tcword);
        (void) readb(&sgint->tcnt2);
        msb = readb(&sgint->tcnt2);
        ct1 = read_c0_count();
    } while (msb);

    /* Stop the counter. */
    writeb(SGINT_TCWORD_CNT2 | SGINT_TCWORD_CALL | SGINT_TCWORD_MSWST,
           &sgint->tcword);
    /*
     * Return the difference, this is how far the r4k counter increments
     * for every 1/HZ seconds. We round off the nearest 1 MHz of master
     * clock (= 1000000 / HZ / 2).
     */

    return (ct1 - ct0) / (500000/HZ) * (500000/HZ);
}

/*
 * Here we need to calibrate the cycle counter to at least be close.
 */
__init void plat_time_init(void)
{
    unsigned long r4k_ticks[3];
    unsigned long r4k_tick;

    /*
     * Figure out the r4k offset, the algorithm is very simple and works in
     * _all_ cases as long as the 8254 counter register itself works ok (as
     * an interrupt driving timer it does not because of bug, this is why
     * we are using the onchip r4k counter/compare register to serve this
     * purpose, but for r4k_offset calculation it will work ok for us).
     * There are other very complicated ways of performing this calculation
     * but this one works just fine so I am not going to futz around. ;-)
     */
    printk(KERN_INFO "Calibrating system timer... ");
    dosample(); /* Prime cache. */
    dosample(); /* Prime cache. */
    /* Zero is NOT an option. */
    do {
        r4k_ticks[0] = dosample();
    } while (!r4k_ticks[0]);
    do {
        r4k_ticks[1] = dosample();
    } while (!r4k_ticks[1]);

    if (r4k_ticks[0] != r4k_ticks[1]) {
        printk("warning: timer counts differ, retrying... ");
        r4k_ticks[2] = dosample();
        if (r4k_ticks[2] == r4k_ticks[0]
            || r4k_ticks[2] == r4k_ticks[1])
            r4k_tick = r4k_ticks[2];
        else {
            printk("disagreement, using average... ");
            r4k_tick = (r4k_ticks[0] + r4k_ticks[1]
                   + r4k_ticks[2]) / 3;
        }
    } else
        r4k_tick = r4k_ticks[0];

    printk("%d [%d.%04d MHz CPU]\n", (int) r4k_tick,
        (int) (r4k_tick / (500000 / HZ)),
        (int) (r4k_tick % (500000 / HZ)));

    mips_hpt_frequency = r4k_tick * HZ;

    if (ip22_is_fullhouse())
        setup_pit_timer();
}

/* Generic SGI handler for (spurious) 8254 interrupts */
void __irq_entry indy_8254timer_irq(void)
{
    int irq = SGI_8254_0_IRQ;
    ULONG cnt;
    char c;

    irq_enter();
    kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
    printk(KERN_ALERT "Oops, got 8254 interrupt.\n");
    ArcRead(0, &c, 1, &cnt);
    ArcEnterInteractiveMode();
    irq_exit();
}