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
  10 #include <asm/io.h>
  11 #include <asm/irq.h>
  12
  13 #include <asm/mach/time.h>
  14
  15 #include "common.h"
  16
  17 /*
  18  * ISA timer tick support
  19  */
  20 #define mSEC_10_from_14 ((14318180 + 100) / 200)
  21
  22 static unsigned long isa_gettimeoffset(void)
  23 {
  24         int count;
  25
  26         static int count_p = (mSEC_10_from_14/6);    /* for the first call after boot */
  27         static unsigned long jiffies_p = 0;
  28
  29         /*
  30          * cache volatile jiffies temporarily; we have IRQs turned off.
  31          */
  32         unsigned long jiffies_t;
  33
  34         /* timer count may underflow right here */
  35         outb_p(0x00, 0x43);     /* latch the count ASAP */
  36
  37         count = inb_p(0x40);    /* read the latched count */
  38
  39         /*
  40          * We do this guaranteed double memory access instead of a _p
  41          * postfix in the previous port access. Wheee, hackady hack
  42          */
  43         jiffies_t = jiffies;
  44
  45         count |= inb_p(0x40) << 8;
  46
  47         /* Detect timer underflows.  If we haven't had a timer tick since
  48            the last time we were called, and time is apparently going
  49            backwards, the counter must have wrapped during this routine. */
  50         if ((jiffies_t == jiffies_p) && (count > count_p))
  51                 count -= (mSEC_10_from_14/6);
  52         else
  53                 jiffies_p = jiffies_t;
  54
  55         count_p = count;
  56
  57         count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);
  58         count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);
  59
  60         return count;
  61 }
  62
  63 static irqreturn_t
  64 isa_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
  65 {
  66         write_seqlock(&xtime_lock);
  67         timer_tick(regs);
  68         write_sequnlock(&xtime_lock);
  69         return IRQ_HANDLED;
  70 }
  71
  72 static struct irqaction isa_timer_irq = {
  73         .name           = "ISA timer tick",
  74         .handler        = isa_timer_interrupt,
  75         .flags          = SA_INTERRUPT,
  76 };
  77
  78 static void __init isa_timer_init(void)
  79 {
  80         isa_rtc_init();
  81
  82         /* enable PIT timer */
  83         /* set for periodic (4) and LSB/MSB write (0x30) */
  84         outb(0x34, 0x43);
  85         outb((mSEC_10_from_14/6) & 0xFF, 0x40);
  86         outb((mSEC_10_from_14/6) >> 8, 0x40);
  87
  88         setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);
  89 }
  90
  91 struct sys_timer isa_timer = {
  92         .init           = isa_timer_init,
  93         .offset         = isa_gettimeoffset,
  94 };