/* *  linux/arch/arm/mach-footbridge/isa-timer.c * *  Copyright (C) 1998 Russell King. *  Copyright (C) 1998 Phil Blundell */#include <linux/init.h>#include <linux/interrupt.h>#include <asm/io.h>#include <asm/irq.h>#include <asm/mach/time.h>#include "common.h"/* * ISA timer tick support */#define mSEC_10_from_14 ((14318180 + 100) / 200)static unsigned long isa_gettimeoffset(void){	int count;	static int count_p = (mSEC_10_from_14/6);    /* for the first call after boot */	static unsigned long jiffies_p = 0;	/*	 * cache volatile jiffies temporarily; we have IRQs turned off. 	 */	unsigned long jiffies_t;	/* timer count may underflow right here */	outb_p(0x00, 0x43);	/* latch the count ASAP */	count = inb_p(0x40);	/* read the latched count */	/*	 * We do this guaranteed double memory access instead of a _p 	 * postfix in the previous port access. Wheee, hackady hack	 */ 	jiffies_t = jiffies;	count |= inb_p(0x40) << 8;	/* Detect timer underflows.  If we haven't had a timer tick since 	   the last time we were called, and time is apparently going	   backwards, the counter must have wrapped during this routine. */	if ((jiffies_t == jiffies_p) && (count > count_p))		count -= (mSEC_10_from_14/6);	else		jiffies_p = jiffies_t;	count_p = count;	count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);	count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);	return count;}static irqreturn_tisa_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs){	write_seqlock(&xtime_lock);	timer_tick(regs);	write_sequnlock(&xtime_lock);	return IRQ_HANDLED;}static struct irqaction isa_timer_irq = {	.name		= "ISA timer tick",	.handler	= isa_timer_interrupt,	.flags		= SA_INTERRUPT | SA_TIMER,};static void __init isa_timer_init(void){	isa_rtc_init();	/* enable PIT timer */	/* set for periodic (4) and LSB/MSB write (0x30) */	outb(0x34, 0x43);	outb((mSEC_10_from_14/6) & 0xFF, 0x40);	outb((mSEC_10_from_14/6) >> 8, 0x40);	setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);}struct sys_timer isa_timer = {	.init		= isa_timer_init,	.offset		= isa_gettimeoffset,};