ntp: Access tick_length variable via ntp_tick_length()

Currently the NTP managed tick_length value is accessed globally,
in preparations for locking cleanups, make sure it is accessed via
a function and mark it as static.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index ae7e136..f131ba6 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -28,7 +28,7 @@
 /* ACTHZ period (nsecs): */
 unsigned long			tick_nsec;
 
-u64				tick_length;
+static u64			tick_length;
 static u64			tick_length_base;
 
 static struct hrtimer		leap_timer;
@@ -360,6 +360,13 @@
 	pps_clear();
 }
 
+
+u64 ntp_tick_length(void)
+{
+	return tick_length;
+}
+
+
 /*
  * Leap second processing. If in leap-insert state at the end of the
  * day, the system clock is set back one second; if in leap-delete
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index f5d4d22..cdae246 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -811,7 +811,7 @@
 	 * Now calculate the error in (1 << look_ahead) ticks, but first
 	 * remove the single look ahead already included in the error.
 	 */
-	tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
+	tick_error = ntp_tick_length() >> (timekeeper.ntp_error_shift + 1);
 	tick_error -= timekeeper.xtime_interval >> 1;
 	error = ((error - tick_error) >> look_ahead) + tick_error;
 
@@ -994,7 +994,7 @@
 	timekeeper.raw_time.tv_nsec = raw_nsecs;
 
 	/* Accumulate error between NTP and clock interval */
-	timekeeper.ntp_error += tick_length << shift;
+	timekeeper.ntp_error += ntp_tick_length() << shift;
 	timekeeper.ntp_error -=
 	    (timekeeper.xtime_interval + timekeeper.xtime_remainder) <<
 				(timekeeper.ntp_error_shift + shift);
@@ -1042,7 +1042,7 @@
 	shift = ilog2(offset) - ilog2(timekeeper.cycle_interval);
 	shift = max(0, shift);
 	/* Bound shift to one less then what overflows tick_length */
-	maxshift = (8*sizeof(tick_length) - (ilog2(tick_length)+1)) - 1;
+	maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1;
 	shift = min(shift, maxshift);
 	while (offset >= timekeeper.cycle_interval) {
 		offset = logarithmic_accumulation(offset, shift);