arch/mips/sgi-ip22/ip22-time.c

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Time operations for IP22 machines. Original code may come from
   7  * Ralf Baechle or David S. Miller (sorry guys, i'm really not sure)
   8  *
   9  * Copyright (C) 2001 by Ladislav Michl
  10  * Copyright (C) 2003, 06 Ralf Baechle (ralf@linux-mips.org)
  11  */
  12 #include <linux/bcd.h>
  13 #include <linux/init.h>
  14 #include <linux/irq.h>
  15 #include <linux/kernel.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/kernel_stat.h>
  18 #include <linux/time.h>
  19
  20 #include <asm/cpu.h>
  21 #include <asm/mipsregs.h>
  22 #include <asm/i8253.h>
  23 #include <asm/io.h>
  24 #include <asm/irq.h>
  25 #include <asm/time.h>
  26 #include <asm/sgialib.h>
  27 #include <asm/sgi/ioc.h>
  28 #include <asm/sgi/hpc3.h>
  29 #include <asm/sgi/ip22.h>
  30
  31 static unsigned long dosample(void)
  32 {
  33         u32 ct0, ct1;
  34         u8 msb, lsb;
  35
  36         /* Start the counter. */
  37         sgint->tcword = (SGINT_TCWORD_CNT2 | SGINT_TCWORD_CALL |
  38                          SGINT_TCWORD_MRGEN);
  39         sgint->tcnt2 = SGINT_TCSAMP_COUNTER & 0xff;
  40         sgint->tcnt2 = SGINT_TCSAMP_COUNTER >> 8;
  41
  42         /* Get initial counter invariant */
  43         ct0 = read_c0_count();
  44
  45         /* Latch and spin until top byte of counter2 is zero */
  46         do {
  47                 writeb(SGINT_TCWORD_CNT2 | SGINT_TCWORD_CLAT, &sgint->tcword);
  48                 lsb = readb(&sgint->tcnt2);
  49                 msb = readb(&sgint->tcnt2);
  50                 ct1 = read_c0_count();
  51         } while (msb);
  52
  53         /* Stop the counter. */
  54         writeb(SGINT_TCWORD_CNT2 | SGINT_TCWORD_CALL | SGINT_TCWORD_MSWST,
  55                &sgint->tcword);
  56         /*
  57          * Return the difference, this is how far the r4k counter increments
  58          * for every 1/HZ seconds. We round off the nearest 1 MHz of master
  59          * clock (= 1000000 / HZ / 2).
  60          */
  61
  62         return (ct1 - ct0) / (500000/HZ) * (500000/HZ);
  63 }
  64
  65 /*
  66  * Here we need to calibrate the cycle counter to at least be close.
  67  */
  68 __init void plat_time_init(void)
  69 {
  70         unsigned long r4k_ticks[3];
  71         unsigned long r4k_tick;
  72
  73         /*
  74          * Figure out the r4k offset, the algorithm is very simple and works in
  75          * _all_ cases as long as the 8254 counter register itself works ok (as
  76          * an interrupt driving timer it does not because of bug, this is why
  77          * we are using the onchip r4k counter/compare register to serve this
  78          * purpose, but for r4k_offset calculation it will work ok for us).
  79          * There are other very complicated ways of performing this calculation
  80          * but this one works just fine so I am not going to futz around. ;-)
  81          */
  82         printk(KERN_INFO "Calibrating system timer... ");
  83         dosample();     /* Prime cache. */
  84         dosample();     /* Prime cache. */
  85         /* Zero is NOT an option. */
  86         do {
  87                 r4k_ticks[0] = dosample();
  88         } while (!r4k_ticks[0]);
  89         do {
  90                 r4k_ticks[1] = dosample();
  91         } while (!r4k_ticks[1]);
  92
  93         if (r4k_ticks[0] != r4k_ticks[1]) {
  94                 printk("warning: timer counts differ, retrying... ");
  95                 r4k_ticks[2] = dosample();
  96                 if (r4k_ticks[2] == r4k_ticks[0]
  97                     || r4k_ticks[2] == r4k_ticks[1])
  98                         r4k_tick = r4k_ticks[2];
  99                 else {
 100                         printk("disagreement, using average... ");
 101                         r4k_tick = (r4k_ticks[0] + r4k_ticks[1]
 102                                    + r4k_ticks[2]) / 3;
 103                 }
 104         } else
 105                 r4k_tick = r4k_ticks[0];
 106
 107         printk("%d [%d.%04d MHz CPU]\n", (int) r4k_tick,
 108                 (int) (r4k_tick / (500000 / HZ)),
 109                 (int) (r4k_tick % (500000 / HZ)));
 110
 111         mips_hpt_frequency = r4k_tick * HZ;
 112
 113         if (ip22_is_fullhouse())
 114                 setup_pit_timer();
 115 }
 116
 117 /* Generic SGI handler for (spurious) 8254 interrupts */
 118 void indy_8254timer_irq(void)
 119 {
 120         int irq = SGI_8254_0_IRQ;
 121         ULONG cnt;
 122         char c;
 123
 124         irq_enter();
 125         kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
 126         printk(KERN_ALERT "Oops, got 8254 interrupt.\n");
 127         ArcRead(0, &c, 1, &cnt);
 128         ArcEnterInteractiveMode();
 129         irq_exit();
 130 }