tick/sched: Add function description for tick_nohz_next_event()

The return value of tick_nohz_next_event() is not obvious at the first
glance. Add a kernel-doc compatible function description which also covers
return values.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240123164702.55612-4-anna-maria@linutronix.de

kernel/time/tick-sched.c

@@ -799,6 +799,16 @@ static inline bool local_timer_softirq_pending(void)
 	return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
 }
 
+/**
+ * tick_nohz_next_event() - return the clock monotonic based next event
+ * @ts:		pointer to tick_sched struct
+ * @cpu:	CPU number
+ *
+ * Return:
+ * *%0		- When the next event is a maximum of TICK_NSEC in the future
+ *		  and the tick is not stopped yet
+ * *%next_event	- Next event based on clock monotonic
+ */
 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
 {
 	u64 basemono, next_tick, delta, expires;