timekeeping: Refactor timekeeping helpers

Simplify the usage of timekeeping sanity checking, in preparation for
consolidating timekeeping helpers. This works towards eliminating
timekeeping_delta_to_ns() in favour of timekeeping_cycles_to_ns().

No functional change.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-14-adrian.hunter@intel.com

kernel/time/timekeeping.c

@@ -237,7 +237,7 @@ static void timekeeping_check_update(struct timekeeper *tk, u64 offset)
 	}
 }
 
-static inline u64 timekeeping_get_delta(const struct tk_read_base *tkr)
+static inline u64 timekeeping_debug_get_delta(const struct tk_read_base *tkr)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
 	u64 now, last, mask, max, delta;
@@ -281,17 +281,9 @@ static inline u64 timekeeping_get_delta(const struct tk_read_base *tkr)
 static inline void timekeeping_check_update(struct timekeeper *tk, u64 offset)
 {
 }
-static inline u64 timekeeping_get_delta(const struct tk_read_base *tkr)
+static inline u64 timekeeping_debug_get_delta(const struct tk_read_base *tkr)
 {
-	u64 cycle_now, delta;
-
-	/* read clocksource */
-	cycle_now = tk_clock_read(tkr);
-
-	/* calculate the delta since the last update_wall_time */
-	delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
-
-	return delta;
+	BUG();
 }
 #endif
 
@@ -396,10 +388,10 @@ static __always_inline u64 __timekeeping_get_ns(const struct tk_read_base *tkr)
 
 static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr)
 {
-	u64 delta;
+	if (IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING))
+		return timekeeping_delta_to_ns(tkr, timekeeping_debug_get_delta(tkr));
 
-	delta = timekeeping_get_delta(tkr);
-	return timekeeping_delta_to_ns(tkr, delta);
+	return __timekeeping_get_ns(tkr);
 }
 
 /**