1 files changed, 118 insertions, 0 deletions
diff --git a/arch/i386/kernel/i8253.c b/arch/i386/kernel/i8253.c
new file mode 100644
index 000000000000..477b24daff53
--- /dev/null
+++ b/arch/i386/kernel/i8253.c
@@ -0,0 +1,118 @@
+/*
+ * i8253.c  8253/PIT functions
+ *
+ */
+#include <linux/clocksource.h>
+#include <linux/spinlock.h>
+#include <linux/jiffies.h>
+#include <linux/sysdev.h>
+#include <linux/module.h>
+#include <linux/init.h>
+
+#include <asm/smp.h>
+#include <asm/delay.h>
+#include <asm/i8253.h>
+#include <asm/io.h>
+
+#include "io_ports.h"
+
+DEFINE_SPINLOCK(i8253_lock);
+EXPORT_SYMBOL(i8253_lock);
+
+void setup_pit_timer(void)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&i8253_lock, flags);
+	outb_p(0x34,PIT_MODE);		/* binary, mode 2, LSB/MSB, ch 0 */
+	udelay(10);
+	outb_p(LATCH & 0xff , PIT_CH0);	/* LSB */
+	udelay(10);
+	outb(LATCH >> 8 , PIT_CH0);	/* MSB */
+	spin_unlock_irqrestore(&i8253_lock, flags);
+}
+
+/*
+ * 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(void)
+{
+	unsigned long flags;
+	int count;
+	u32 jifs;
+	static int old_count;
+	static u32 old_jifs;
+
+	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_p(0x00, PIT_MODE);	/* latch the count ASAP */
+	count = inb_p(PIT_CH0);	/* read the latched count */
+	count |= inb_p(PIT_CH0) << 8;
+
+	/* VIA686a test code... reset the latch if count > max + 1 */
+	if (count > LATCH) {
+		outb_p(0x34, PIT_MODE);
+		outb_p(LATCH & 0xff, PIT_CH0);
+		outb(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;
+
+	spin_unlock_irqrestore(&i8253_lock, flags);
+
+	count = (LATCH - 1) - count;
+
+	return (cycle_t)(jifs * LATCH) + count;
+}
+
+static struct clocksource clocksource_pit = {
+	.name	= "pit",
+	.rating = 110,
+	.read	= pit_read,
+	.mask	= CLOCKSOURCE_MASK(32),
+	.mult	= 0,
+	.shift	= 20,
+};
+
+static int __init init_pit_clocksource(void)
+{
+	if (num_possible_cpus() > 4) /* PIT does not scale! */
+		return 0;
+
+	clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);
+	return clocksource_register(&clocksource_pit);
+}
+module_init(init_pit_clocksource);