arm: sched_clock: Enable HAVE_SCHED_CLOCK support without init_sched_clock

From: Kyungmin Park <[email protected]>

On Samsung Exynos4 series, EVT0 chip uses the s5p_timer with HAVE_SCHED_CLOCK and remains use the MCT timer without init_sched_clock.

The similar combination will be happend with other SOCs. some board use HAVE_SCHED_CLOCK or others are not.

To co-exist the these boards. check the sched_clock_update_fn when sched_clock_postinit is called and return if not defined.

---

index 9a46370..12c6b6b 100644
@@ -70,5 +70,8 @@ void __init init_sched_clock(struct clock_data *cd, void (*update)(void),
 
 void __init sched_clock_postinit(void)
 {
+	/* If init_sched_clock is not called, just return */
+	if (!sched_clock_update_fn)
+		return;
 	sched_clock_poll(sched_clock_timer.data);
 }

So in other words, sched_clock on exynos4 is broken because the update function won't be called, and it'll wrap well below the 64-bit ns range required of it.

NAK.

Right, even though MCT doesn't use the HAVE_SCHED_CLOCK, sched_clock is override with others.
It mean it should be implement the sched_clock for all boards if there are some boards use the HAVE_SCHED_CLOCK.

As I remember, there's attempt to solve the sched_clock registration issue. I'll check it.

Thank you,
Kyungmin Park