timekeeping: Provide time getters for auxiliary clocks

Provide interfaces similar to the ktime_get*() family which provide access
to the auxiliary clocks.

These interfaces have a boolean return value, which indicates whether the
accessed clock is valid or not.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250625183757.868342628@linutronix.de

Author: KAGA-KOKO

include/linux/posix-timers.h

@@ -37,6 +37,11 @@ static inline int clockid_to_fd(const clockid_t clk)
 	return ~(clk >> 3);
 }
 
+static inline bool clockid_aux_valid(clockid_t id)
+{
+	return IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS) && id >= CLOCK_AUX && id <= CLOCK_AUX_LAST;
+}
+
 #ifdef CONFIG_POSIX_TIMERS
 
 #include <linux/signal_types.h>

include/linux/timekeeping.h

@@ -263,6 +263,17 @@ extern bool timekeeping_rtc_skipresume(void);
 
 extern void timekeeping_inject_sleeptime64(const struct timespec64 *delta);
 
+/*
+ * Auxiliary clock interfaces
+ */
+#ifdef CONFIG_POSIX_AUX_CLOCKS
+extern bool ktime_get_aux(clockid_t id, ktime_t *kt);
+extern bool ktime_get_aux_ts64(clockid_t id, struct timespec64 *kt);
+#else
+static inline bool ktime_get_aux(clockid_t id, ktime_t *kt) { return false; }
+static inline bool ktime_get_aux_ts64(clockid_t id, struct timespec64 *kt) { return false; }
+#endif
+
 /**
  * struct system_time_snapshot - simultaneous raw/real time capture with
  *				 counter value

kernel/time/timekeeping.c

@@ -2664,6 +2664,18 @@ EXPORT_SYMBOL(hardpps);
  */
 static unsigned long aux_timekeepers;
 
+static inline unsigned int clockid_to_tkid(unsigned int id)
+{
+	return TIMEKEEPER_AUX_FIRST + id - CLOCK_AUX;
+}
+
+static inline struct tk_data *aux_get_tk_data(clockid_t id)
+{
+	if (!clockid_aux_valid(id))
+		return NULL;
+	return &timekeeper_data[clockid_to_tkid(id)];
+}
+
 /* Invoked from timekeeping after a clocksource change */
 static void tk_aux_update_clocksource(void)
 {
@@ -2684,6 +2696,59 @@ static void tk_aux_update_clocksource(void)
 	}
 }
 
+/**
+ * ktime_get_aux - Get time for a AUX clock
+ * @id:	ID of the clock to read (CLOCK_AUX...)
+ * @kt:	Pointer to ktime_t to store the time stamp
+ *
+ * Returns: True if the timestamp is valid, false otherwise
+ */
+bool ktime_get_aux(clockid_t id, ktime_t *kt)
+{
+	struct tk_data *aux_tkd = aux_get_tk_data(id);
+	struct timekeeper *aux_tk;
+	unsigned int seq;
+	ktime_t base;
+	u64 nsecs;
+
+	WARN_ON(timekeeping_suspended);
+
+	if (!aux_tkd)
+		return false;
+
+	aux_tk = &aux_tkd->timekeeper;
+	do {
+		seq = read_seqcount_begin(&aux_tkd->seq);
+		if (!aux_tk->clock_valid)
+			return false;
+
+		base = ktime_add(aux_tk->tkr_mono.base, aux_tk->offs_aux);
+		nsecs = timekeeping_get_ns(&aux_tk->tkr_mono);
+	} while (read_seqcount_retry(&aux_tkd->seq, seq));
+
+	*kt = ktime_add_ns(base, nsecs);
+	return true;
+}
+EXPORT_SYMBOL_GPL(ktime_get_aux);
+
+/**
+ * ktime_get_aux_ts64 - Get time for a AUX clock
+ * @id:	ID of the clock to read (CLOCK_AUX...)
+ * @ts:	Pointer to timespec64 to store the time stamp
+ *
+ * Returns: True if the timestamp is valid, false otherwise
+ */
+bool ktime_get_aux_ts64(clockid_t id, struct timespec64 *ts)
+{
+	ktime_t now;
+
+	if (!ktime_get_aux(id, &now))
+		return false;
+	*ts = ktime_to_timespec64(now);
+	return true;
+}
+EXPORT_SYMBOL_GPL(ktime_get_aux_ts64);
+
 static __init void tk_aux_setup(void)
 {
 	for (int i = TIMEKEEPER_AUX_FIRST; i <= TIMEKEEPER_AUX_LAST; i++)