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ip22-time.c

/*
 * 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 (ralf@linux-mips.org)
 */
#include <linux/bcd.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 <asm/cpu.h>
#include <asm/mipsregs.h>
#include <asm/i8253.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, lsb;

      /* 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);
            lsb = 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 indy_8254timer_irq(void)
{
      int irq = SGI_8254_0_IRQ;
      ULONG cnt;
      char c;

      irq_enter();
      kstat_this_cpu.irqs[irq]++;
      printk(KERN_ALERT "Oops, got 8254 interrupt.\n");
      ArcRead(0, &c, 1, &cnt);
      ArcEnterInteractiveMode();
      irq_exit();
}

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