MIPS: csrc-ioasic: Implement read_sched_clock

Use DEC I/O ASIC's free-running counter for sched_clock source. This
implementation will give high resolution cputime accounting.

Acked-by: Maciej W. Rozycki <macro@linux-mips.org>
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/9482/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/csrc-ioasic.c

@@ -14,6 +14,7 @@
  *  GNU General Public License for more details.
  */
 #include <linux/clocksource.h>
+#include <linux/sched_clock.h>
 #include <linux/init.h>
 
 #include <asm/ds1287.h>
@@ -33,6 +34,11 @@ static struct clocksource clocksource_dec = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static u64 notrace dec_ioasic_read_sched_clock(void)
+{
+	return ioasic_read(IO_REG_FCTR);
+}
+
 int __init dec_ioasic_clocksource_init(void)
 {
 	unsigned int freq;
@@ -61,5 +67,8 @@ int __init dec_ioasic_clocksource_init(void)
 
 	clocksource_dec.rating = 200 + freq / 10000000;
 	clocksource_register_hz(&clocksource_dec, freq);
+
+	sched_clock_register(dec_ioasic_read_sched_clock, 32, freq);
+
 	return 0;
 }