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: NJohn Stultz <john.stultz@linaro.org>

include/linux/timex.h

@@ -250,7 +250,7 @@ extern void ntp_clear(void);
 #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
 
 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
-extern u64 tick_length;
+extern u64 ntp_tick_length(void);
 
 extern void second_overflow(void);
 extern int do_adjtimex(struct timex *);

kernel/time/ntp.c

@@ -28,7 +28,7 @@ unsigned long			tick_usec = TICK_USEC;
 /* 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 @@ void ntp_clear(void)
 	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

kernel/time/timekeeping.c

@@ -811,7 +811,7 @@ static __always_inline int timekeeping_bigadjust(s64 error, s64 *interval,
 	 * 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 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
 	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 @@ static void update_wall_time(void)
 	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);