timekeeping: Add clock_valid flag to timekeeper

In preparation for supporting independent auxiliary timekeepers, add a
clock valid field and set it to true for the system timekeeper.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250519083026.287145536@linutronix.de

Author: KAGA-KOKO

include/linux/timekeeper_internal.h

@@ -73,6 +73,7 @@ struct tk_read_base {
  * @raw_sec:			CLOCK_MONOTONIC_RAW  time in seconds
  * @clock_was_set_seq:		The sequence number of clock was set events
  * @cs_was_changed_seq:		The sequence number of clocksource change events
+ * @clock_valid:		Indicator for valid clock
  * @monotonic_to_boot:		CLOCK_MONOTONIC to CLOCK_BOOTTIME offset
  * @cycle_interval:		Number of clock cycles in one NTP interval
  * @xtime_interval:		Number of clock shifted nano seconds in one NTP
@@ -149,6 +150,7 @@ struct timekeeper {
 	/* Cachline 3 and 4 (timekeeping internal variables): */
 	unsigned int		clock_was_set_seq;
 	u8			cs_was_changed_seq;
+	u8			clock_valid;
 
 	struct timespec64	monotonic_to_boot;
 

kernel/time/timekeeping.c

@@ -1665,11 +1665,12 @@ read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
 	*boot_offset = ns_to_timespec64(local_clock());
 }
 
-static __init void tkd_basic_setup(struct tk_data *tkd, enum timekeeper_ids tk_id)
+static __init void tkd_basic_setup(struct tk_data *tkd, enum timekeeper_ids tk_id, bool valid)
 {
 	raw_spin_lock_init(&tkd->lock);
 	seqcount_raw_spinlock_init(&tkd->seq, &tkd->lock);
 	tkd->timekeeper.id = tkd->shadow_timekeeper.id = tk_id;
+	tkd->timekeeper.clock_valid = tkd->shadow_timekeeper.clock_valid = valid;
 }
 
 /*
@@ -1699,7 +1700,7 @@ void __init timekeeping_init(void)
 	struct timekeeper *tks = &tk_core.shadow_timekeeper;
 	struct clocksource *clock;
 
-	tkd_basic_setup(&tk_core, TIMEKEEPER_CORE);
+	tkd_basic_setup(&tk_core, TIMEKEEPER_CORE, true);
 
 	read_persistent_wall_and_boot_offset(&wall_time, &boot_offset);
 	if (timespec64_valid_settod(&wall_time) &&