clocksource: Add __clocksource_updatefreq_hz/khz methods

To properly handle clocksources that change frequencies
at the clocksource->enable() point, this patch adds
a method that will update the clocksource's mult/shift and
max_idle_ns values.

Signed-off-by: John Stultz <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/clocksource.h

···
  */
 extern int
 __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq);
+extern void
+__clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq);
 
 static inline int clocksource_register_hz(struct clocksource *cs, u32 hz)
 {
···
 	return __clocksource_register_scale(cs, 1000, khz);
 }
 
+static inline void __clocksource_updatefreq_hz(struct clocksource *cs, u32 hz)
+{
+	__clocksource_updatefreq_scale(cs, 1, hz);
+}
+
+static inline void __clocksource_updatefreq_khz(struct clocksource *cs, u32 khz)
+{
+	__clocksource_updatefreq_scale(cs, 1000, khz);
+}
 
 static inline void
 clocksource_calc_mult_shift(struct clocksource *cs, u32 freq, u32 minsec)

kernel/time/clocksource.c

···
 #define MAX_UPDATE_LENGTH 5 /* Seconds */
 
 /**
+ * __clocksource_updatefreq_scale - Used update clocksource with new freq
+ * @t:		clocksource to be registered
+ * @scale:	Scale factor multiplied against freq to get clocksource hz
+ * @freq:	clocksource frequency (cycles per second) divided by scale
+ *
+ * This should only be called from the clocksource->enable() method.
+ *
+ * This *SHOULD NOT* be called directly! Please use the
+ * clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
+ */
+void __clocksource_updatefreq_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);
+}
+EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
+
+/**
  * __clocksource_register_scale - Used to install new clocksources
  * @t:		clocksource to be registered
  * @scale:	Scale factor multiplied against freq to get clocksource hz
···
 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);
+	/* Intialize mult/shift and max_idle_ns */
+	__clocksource_updatefreq_scale(cs, scale, freq);
 
+	/* Add clocksource to the clcoksource list */
 	mutex_lock(&clocksource_mutex);
 	clocksource_enqueue(cs);
 	clocksource_select();