arch/arm/mach-footbridge/isa-timer.c

   1 /*
   2  *  linux/arch/arm/mach-footbridge/isa-timer.c
   3  *
   4  *  Copyright (C) 1998 Russell King.
   5  *  Copyright (C) 1998 Phil Blundell
   6  */
   7 #include <linux/init.h>
   8 #include <linux/interrupt.h>
   9 #include <linux/irq.h>
  10 #include <linux/io.h>
  11
  12 #include <asm/irq.h>
  13
  14 #include <asm/mach/time.h>
  15
  16 #include "common.h"
  17
  18 /*
  19  * ISA timer tick support
  20  */
  21 #define mSEC_10_from_14 ((14318180 + 100) / 200)
  22
  23 static unsigned long isa_gettimeoffset(void)
  24 {
  25         int count;
  26
  27         static int count_p = (mSEC_10_from_14/6);    /* for the first call after boot */
  28         static unsigned long jiffies_p = 0;
  29
  30         /*
  31          * cache volatile jiffies temporarily; we have IRQs turned off.
  32          */
  33         unsigned long jiffies_t;
  34
  35         /* timer count may underflow right here */
  36         outb_p(0x00, 0x43);     /* latch the count ASAP */
  37
  38         count = inb_p(0x40);    /* read the latched count */
  39
  40         /*
  41          * We do this guaranteed double memory access instead of a _p
  42          * postfix in the previous port access. Wheee, hackady hack
  43          */
  44         jiffies_t = jiffies;
  45
  46         count |= inb_p(0x40) << 8;
  47
  48         /* Detect timer underflows.  If we haven't had a timer tick since
  49            the last time we were called, and time is apparently going
  50            backwards, the counter must have wrapped during this routine. */
  51         if ((jiffies_t == jiffies_p) && (count > count_p))
  52                 count -= (mSEC_10_from_14/6);
  53         else
  54                 jiffies_p = jiffies_t;
  55
  56         count_p = count;
  57
  58         count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);
  59         count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);
  60
  61         return count;
  62 }
  63
  64 static irqreturn_t
  65 isa_timer_interrupt(int irq, void *dev_id)
  66 {
  67         timer_tick();
  68         return IRQ_HANDLED;
  69 }
  70
  71 static struct irqaction isa_timer_irq = {
  72         .name           = "ISA timer tick",
  73         .handler        = isa_timer_interrupt,
  74         .flags          = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
  75 };
  76
  77 static void __init isa_timer_init(void)
  78 {
  79         /* enable PIT timer */
  80         /* set for periodic (4) and LSB/MSB write (0x30) */
  81         outb(0x34, 0x43);
  82         outb((mSEC_10_from_14/6) & 0xFF, 0x40);
  83         outb((mSEC_10_from_14/6) >> 8, 0x40);
  84
  85         setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);
  86 }
  87
  88 struct sys_timer isa_timer = {
  89         .init           = isa_timer_init,
  90         .offset         = isa_gettimeoffset,
  91 };