1 files changed, 48 insertions, 0 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 1f5dde637457..f08e99c1d561 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -625,6 +625,54 @@ static void clocksource_enqueue(struct clocksource *cs)
         list_add(&cs->list, entry);
 }
 
+
+/*
+ * Maximum time we expect to go between ticks. This includes idle
+ * tickless time. It provides the trade off between selecting a
+ * mult/shift pair that is very precise but can only handle a short
+ * period of time, vs. a mult/shift pair that can handle long periods
+ * of time but isn't as precise.
+ *
+ * This is a subsystem constant, and actual hardware limitations
+ * may override it (ie: clocksources that wrap every 3 seconds).
+ */
+#define MAX_UPDATE_LENGTH 5 /* Seconds */
+
+/**
+ * __clocksource_register_scale - Used to install new clocksources
+ * @t:          clocksource to be registered
+ * @scale:      Scale factor multiplied against freq to get clocksource hz
+ * @freq:       clocksource frequency (cycles per second) divided by scale
+ *
+ * Returns -EBUSY if registration fails, zero otherwise.
+ *
+ * This *SHOULD NOT* be called directly! Please use the
+ * clocksource_register_hz() or clocksource_register_khz helper functions.
+ */
+int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
+{
+
+        /*
+         * Ideally we want to use  some of the limits used in
+         * clocksource_max_deferment, to provide a more informed
+         * MAX_UPDATE_LENGTH. But for now this just gets the
+         * register interface working properly.
+         */
+        clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
+                                      NSEC_PER_SEC/scale,
+                                      MAX_UPDATE_LENGTH*scale);
+        cs->max_idle_ns = clocksource_max_deferment(cs);
+
+        mutex_lock(&clocksource_mutex);
+        clocksource_enqueue(cs);
+        clocksource_select();
+        clocksource_enqueue_watchdog(cs);
+        mutex_unlock(&clocksource_mutex);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(__clocksource_register_scale);
+
+
 /**
  * clocksource_register - Used to install new clocksources
  * @t:          clocksource to be registered