davinci: Implement sched_clock()

Overwrite the default implementation of sched_clock that is based on
jiffies by something more precise. This improves timestamps in ftrace.
Implementation is copied from OMAP platform code.
Signed-off-by: NAndreas Gaeer <Andreas.Gaer@baslerweb.com>
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>

arch/arm/mach-davinci/time.c

@@ -272,14 +272,35 @@ static cycle_t read_cycles(struct clocksource *cs)
 	return (cycles_t)timer32_read(t);
 }
 
+/*
+ * Kernel assumes that sched_clock can be called early but may not have
+ * things ready yet.
+ */
+static cycle_t read_dummy(struct clocksource *cs)
+{
+	return 0;
+}
+
+
 static struct clocksource clocksource_davinci = {
 	.rating		= 300,
-	.read		= read_cycles,
+	.read		= read_dummy,
 	.mask		= CLOCKSOURCE_MASK(32),
 	.shift		= 24,
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+/*
+ * Overwrite weak default sched_clock with something more precise
+ */
+unsigned long long notrace sched_clock(void)
+{
+	const cycle_t cyc = clocksource_davinci.read(&clocksource_davinci);
+
+	return clocksource_cyc2ns(cyc, clocksource_davinci.mult,
+				clocksource_davinci.shift);
+}
+
 /*
  * clockevent
  */
@@ -377,6 +398,7 @@ static void __init davinci_timer_init(void)
 	davinci_clock_tick_rate = clk_get_rate(timer_clk);
 
 	/* setup clocksource */
+	clocksource_davinci.read = read_cycles;
 	clocksource_davinci.name = id_to_name[clocksource_id];
 	clocksource_davinci.mult =
 		clocksource_khz2mult(davinci_clock_tick_rate/1000,