uml: clocksource support

Add clocksource support.
Signed-off-by: NJeff Dike <jdike@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/time.c

@@ -97,6 +97,21 @@ static irqreturn_t um_timer(int irq, void *dev)
 	return IRQ_HANDLED;
 }
 
+static cycle_t itimer_read(void)
+{
+	return os_nsecs();
+}
+
+static struct clocksource itimer_clocksource = {
+	.name		= "itimer",
+	.rating		= 300,
+	.read		= itimer_read,
+	.mask		= CLOCKSOURCE_MASK(64),
+	.mult		= 1,
+	.shift		= 0,
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
 static void __init setup_itimer(void)
 {
 	int err;
@@ -111,6 +126,11 @@ static void __init setup_itimer(void)
 		clockevent_delta2ns(60 * HZ, &itimer_clockevent);
 	itimer_clockevent.min_delta_ns =
 		clockevent_delta2ns(1, &itimer_clockevent);
+	err = clocksource_register(&itimer_clocksource);
+	if (err) {
+		printk(KERN_ERR "clocksource_register returned %d\n", err);
+		return;
+	}
 	clockevents_register_device(&itimer_clockevent);
 }