timers: Split next timer interrupt logic

Split the logic for getting next timer interrupt (no matter of recalculated
or already stored in base->next_expiry) into a separate function named
next_timer_interrupt(). Make it available to local call sites only.

No functional change.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20240221090548.36600-10-anna-maria@linutronix.de

kernel/time/timer.c

@@ -1996,12 +1996,29 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
 	return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
 }
 
+static unsigned long next_timer_interrupt(struct timer_base *base,
+					  unsigned long basej)
+{
+	if (base->next_expiry_recalc)
+		next_expiry_recalc(base);
+
+	/*
+	 * Move next_expiry for the empty base into the future to prevent an
+	 * unnecessary raise of the timer softirq when the next_expiry value
+	 * will be reached even if there is no timer pending.
+	 */
+	if (!base->timers_pending)
+		base->next_expiry = basej + NEXT_TIMER_MAX_DELTA;
+
+	return base->next_expiry;
+}
+
 static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
 					     bool *idle)
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
-	unsigned long nextevt = basej + NEXT_TIMER_MAX_DELTA;
 	u64 expires = KTIME_MAX;
+	unsigned long nextevt;
 
 	/*
 	 * Pretend that there is no timer pending if the cpu is offline.
@@ -2014,24 +2031,13 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
 	}
 
 	raw_spin_lock(&base->lock);
-	if (base->next_expiry_recalc)
-		next_expiry_recalc(base);
+	nextevt = next_timer_interrupt(base, basej);
 
 	if (base->timers_pending) {
-		nextevt = base->next_expiry;
-
 		/* If we missed a tick already, force 0 delta */
 		if (time_before(nextevt, basej))
 			nextevt = basej;
 		expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
-	} else {
-		/*
-		 * Move next_expiry for the empty base into the future to
-		 * prevent a unnecessary raise of the timer softirq when the
-		 * next_expiry value will be reached even if there is no timer
-		 * pending.
-		 */
-		base->next_expiry = nextevt;
 	}
 
 	/*