[PATCH 1/2] rtc: Add flag for dynamic hctosys control

[Akashdeep Kaur]

Add flag to indicate whether RTC has valid absolute time on current
boot. This allows drivers to dynamically communicate RTC validity
per-boot to prevent hctosys from setting system time from invalid
RTC values.
The flag defaults to true for backward compatibility with existing
drivers.

Signed-off-by: Akashdeep Kaur <a-kaur@xxxxxx>
---
 drivers/rtc/class.c | 15 +++++++++++++++
 include/linux/rtc.h |  7 +++++++
 2 files changed, 22 insertions(+)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 01ba04028f1f..cec27c476545 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -63,6 +63,18 @@ static void rtc_hctosys(struct rtc_device *rtc)
 		.tv_nsec = NSEC_PER_SEC >> 1,
 	};
 
+	/*
+	 * If the RTC does not have valid time, do not set system time at boot.
+	 * This can happen when RTC loses power or has never been initialized.
+	 * PM resume compensation will still work via rtc_resume().
+	 */
+	if (!rtc->time_is_valid) {
+		dev_info(rtc->dev.parent,
+			 "hctosys: RTC time not valid, skipping\n");
+		err = -EINVAL;
+		goto err_read;
+	}
+
 	err = rtc_read_time(rtc, &tm);
 	if (err) {
 		dev_err(rtc->dev.parent,
@@ -243,6 +255,9 @@ static struct rtc_device *rtc_allocate_device(void)
 	hrtimer_setup(&rtc->pie_timer, rtc_pie_update_irq, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	rtc->pie_enabled = 0;
 
+	/* Assume RTC has valid time by default. Drivers can override. */
+	rtc->time_is_valid = true;
+
 	set_bit(RTC_FEATURE_ALARM, rtc->features);
 	set_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
 
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 0f43b5027235..f6f982610938 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -152,6 +152,13 @@ struct rtc_device {
 	time64_t offset_secs;
 	bool set_start_time;
 
+	/*
+	 * Set by drivers to indicate RTC has valid absolute time.
+	 * Used to prevent hctosys from using RTC when time is invalid
+	 * (e.g., lost power, never initialized). PM compensation is unaffected.
+	 */
+	bool time_is_valid;
+
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 	struct work_struct uie_task;
 	struct timer_list uie_timer;
-- 
2.34.1