clocksource: convert x86 to generic i8253 clocksource

config X86_32

	def_bool !64BIT

	select CLKSRC_I8253

config X86_64

	def_bool 64BIT

#define PIT_CH0			0x40

#define PIT_CH2			0x42

#define PIT_LATCH	LATCH

extern raw_spinlock_t i8253_lock;

extern struct clock_event_device *global_clock_event;

}

#ifndef CONFIG_X86_64

/*

 * Since the PIT overflows every tick, its not very useful

 * to just read by itself. So use jiffies to emulate a free

 * running counter:

 */

static cycle_t pit_read(struct clocksource *cs)

{

	static int old_count;

	static u32 old_jifs;

	unsigned long flags;

	int count;

	u32 jifs;

	raw_spin_lock_irqsave(&i8253_lock, flags);

	/*

	 * Although our caller may have the read side of xtime_lock,

	 * this is now a seqlock, and we are cheating in this routine

	 * by having side effects on state that we cannot undo if

	 * there is a collision on the seqlock and our caller has to

	 * retry.  (Namely, old_jifs and old_count.)  So we must treat

	 * jiffies as volatile despite the lock.  We read jiffies

	 * before latching the timer count to guarantee that although

	 * the jiffies value might be older than the count (that is,

	 * the counter may underflow between the last point where

	 * jiffies was incremented and the point where we latch the

	 * count), it cannot be newer.

	 */

	jifs = jiffies;

	outb_pit(0x00, PIT_MODE);	/* latch the count ASAP */

	count = inb_pit(PIT_CH0);	/* read the latched count */

	count |= inb_pit(PIT_CH0) << 8;

	/* VIA686a test code... reset the latch if count > max + 1 */

	if (count > LATCH) {

		outb_pit(0x34, PIT_MODE);

		outb_pit(LATCH & 0xff, PIT_CH0);

		outb_pit(LATCH >> 8, PIT_CH0);

		count = LATCH - 1;

	}

	/*

	 * It's possible for count to appear to go the wrong way for a

	 * couple of reasons:

	 *

	 *  1. The timer counter underflows, but we haven't handled the

	 *     resulting interrupt and incremented jiffies yet.

	 *  2. Hardware problem with the timer, not giving us continuous time,

	 *     the counter does small "jumps" upwards on some Pentium systems,

	 *     (see c't 95/10 page 335 for Neptun bug.)

	 *

	 * Previous attempts to handle these cases intelligently were

	 * buggy, so we just do the simple thing now.

	 */

	if (count > old_count && jifs == old_jifs)

		count = old_count;

	old_count = count;

	old_jifs = jifs;

	raw_spin_unlock_irqrestore(&i8253_lock, flags);

	count = (LATCH - 1) - count;

	return (cycle_t)(jifs * LATCH) + count;

}

static struct clocksource pit_cs = {

	.name		= "pit",

	.rating		= 110,

	.read		= pit_read,

	.mask		= CLOCKSOURCE_MASK(32),

	.mult		= 0,

	.shift		= 20,

};

static int __init init_pit_clocksource(void)

{

	 /*

	    pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)

		return 0;

	pit_cs.mult = clocksource_hz2mult(CLOCK_TICK_RATE, pit_cs.shift);

	return clocksource_register(&pit_cs);

	return clocksource_i8253_init();

}

arch_initcall(init_pit_clocksource);