MIPS: sgi-ip27: Implement read_sched_clock

Use ip27 hub real time counter for sched_clock source. This implementation
will give high resolution cputime accounting.
Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: macro@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9483/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/sgi-ip27/ip27-timer.c

@@ -7,6 +7,7 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
+#include <linux/sched_clock.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
 #include <linux/param.h>
@@ -159,11 +160,18 @@ struct clocksource hub_rt_clocksource = {
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static u64 notrace hub_rt_read_sched_clock(void)
+{
+	return REMOTE_HUB_L(cputonasid(0), PI_RT_COUNT);
+}
+
 static void __init hub_rt_clocksource_init(void)
 {
 	struct clocksource *cs = &hub_rt_clocksource;
 
 	clocksource_register_hz(cs, CYCLES_PER_SEC);
+
+	sched_clock_register(hub_rt_read_sched_clock, 52, CYCLES_PER_SEC);
 }
 
 void __init plat_time_init(void)