clocksource: convert x86 to generic i8253 clocksource

Convert x86 i8253 clocksource code to use generic i8253 clocksource.
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/x86/Kconfig

@@ -8,6 +8,7 @@ config 64BIT
 
 config X86_32
 	def_bool !64BIT
+	select CLKSRC_I8253
 
 config X86_64
 	def_bool 64BIT

arch/x86/include/asm/i8253.h

@@ -6,6 +6,8 @@
 #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;

arch/x86/kernel/i8253.c

@@ -117,81 +117,6 @@ void __init setup_pit_timer(void)
 }
 
 #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)
 {
 	 /*
@@ -205,9 +130,7 @@ 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);