microblaze: Improve ftrace time measuring

I had to comment sched_clock generic function because of broken toolchain.
It is fine grain timing.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/include/asm/setup.h

@@ -28,8 +28,6 @@ void disable_early_printk(void);
 void heartbeat(void);
 void setup_heartbeat(void);
 
-unsigned long long sched_clock(void);
-
 #   ifdef CONFIG_MMU
 extern void mmu_reset(void);
 extern void early_console_reg_tlb_alloc(unsigned int addr);

arch/microblaze/kernel/timer.c

@@ -235,6 +235,12 @@ static int __init microblaze_clocksource_init(void)
 	return 0;
 }
 
+/*
+ * We have to protect accesses before timer initialization
+ * and return 0 for sched_clock function below.
+ */
+static int timer_initialized;
+
 void __init time_init(void)
 {
 	u32 irq, i = 0;
@@ -289,4 +295,15 @@ void __init time_init(void)
 #endif
 	microblaze_clocksource_init();
 	microblaze_clockevent_init();
+	timer_initialized = 1;
+}
+
+unsigned long long notrace sched_clock(void)
+{
+	if (timer_initialized) {
+		struct clocksource *cs = &clocksource_microblaze;
+		cycle_t cyc = cs->read(NULL);
+		return clocksource_cyc2ns(cyc, cs->mult, cs->shift);
+	}
+	return 0;
 }