linux-kernel - [PATCH v3 2/5] rtc: pcf85363: support reporting battery switch-over via RTC

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Message-Id: <20251119083336.2241142-2-lakshay.piplani@nxp.com>
Date: Wed, 19 Nov 2025 14:03:33 +0530
From: Lakshay Piplani <lakshay.piplani@....com>
To: alexandre.belloni@...tlin.com,
	linux-rtc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	devicetree@...r.kernel.org,
	wim@...ux-watchdog.org,
	linux@...ck-us.net,
	linux-watchdog@...r.kernel.org
Cc: vikash.bansal@....com,
	priyanka.jain@....com,
	shashank.rebbapragada@....com,
	Lakshay Piplani <lakshay.piplani@....com>
Subject: [PATCH v3 2/5] rtc: pcf85363: support reporting battery switch-over via RTC_VL

Add battery switch-over reporting for PCF85263/PCF85363 using the standard
RTC_VL_* ioctl interface. When the backup supply takes over, the BSF flag
is exposed to userspace through RTC_VL_READ and can be cleared using
RTC_VL_CLR.

This allows applications to detect loss of main power without relying on
non-standard interfaces.

Signed-off-by: Lakshay Piplani <lakshay.piplani@....com>
---
V2 -> V3:
- Split into separate patches as suggested:
  - Battery switch-over detection.
  - Timestamp recording for TS pin and battery switch-over events.
  - Offset calibration.
  - Watchdog timer (to be reviewed by watchdog maintainers).
- Dropped Alarm2 support
- Switched to rtc_add_group() for sysfs attributes
- Removed failure paths after RTC device registration as per subsystem guidelines.
V1 -> V2:
- Watchdog related changes due to removal of vendor specific properties
  from device tree
  * remove vendor DT knobs (enable/timeout/stepsize/repeat)
  * use watchdog_init_timeout (with 10s default)
  * derive clock_sel from final timeout
  * default, repeat=true (repeat mode)
- Fixed uninitalised warning on 'ret' (reported by kernel test robot)
- Use dev_dbg instead of dev_info for debug related print messages
- Minor cleanup and commentsi

 drivers/rtc/rtc-pcf85363.c | 49 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-pcf85363.c b/drivers/rtc/rtc-pcf85363.c
index 540042b9eec8..c03d5a65c5f7 100644
--- a/drivers/rtc/rtc-pcf85363.c
+++ b/drivers/rtc/rtc-pcf85363.c
@@ -14,6 +14,7 @@
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/bcd.h>
+#include <linux/device.h>
 #include <linux/of.h>
 #include <linux/regmap.h>
 
@@ -295,23 +296,67 @@ static int pcf85363_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 static irqreturn_t pcf85363_rtc_handle_irq(int irq, void *dev_id)
 {
 	struct pcf85363 *pcf85363 = i2c_get_clientdata(dev_id);
+	bool handled = false;
 	unsigned int flags;
 	int err;
 
 	err = regmap_read(pcf85363->regmap, CTRL_FLAGS, &flags);
+
 	if (err)
 		return IRQ_NONE;
 
+	if (flags) {
+		dev_dbg(&pcf85363->rtc->dev, "IRQ flags: 0x%02x%s%s\n",
+			flags, (flags & FLAGS_A1F) ? " [A1F]" : "",
+			(flags & FLAGS_BSF) ? " [BSF]" : "");
+	}
+
 	if (flags & FLAGS_A1F) {
 		rtc_update_irq(pcf85363->rtc, 1, RTC_IRQF | RTC_AF);
 		regmap_update_bits(pcf85363->regmap, CTRL_FLAGS, FLAGS_A1F, 0);
-		return IRQ_HANDLED;
+		handled = true;
 	}
 
-	return IRQ_NONE;
+	if (flags & FLAGS_BSF) {
+		regmap_update_bits(pcf85363->regmap, CTRL_FLAGS, FLAGS_BSF, 0);
+		handled = true;
+	}
+
+	return handled ? IRQ_HANDLED : IRQ_NONE;
+}
+
+static int pcf85363_rtc_ioctl(struct device *dev,
+			      unsigned int cmd, unsigned long arg)
+{
+	struct pcf85363 *pcf85363 = dev_get_drvdata(dev);
+	unsigned int val;
+	int ret;
+
+	switch (cmd) {
+	case RTC_VL_READ: {
+		u32 status = 0;
+
+		ret = regmap_read(pcf85363->regmap, CTRL_FLAGS, &val);
+
+		if (ret)
+			return ret;
+
+		if (val & FLAGS_BSF)
+			status |= RTC_VL_BACKUP_SWITCH;
+
+		return put_user(status, (u32 __user *)arg);
+	}
+
+	case RTC_VL_CLR:
+		return regmap_update_bits(pcf85363->regmap, CTRL_FLAGS, FLAGS_BSF, 0);
+
+	default:
+		return -ENOIOCTLCMD;
+	}
 }
 
 static const struct rtc_class_ops rtc_ops = {
+	.ioctl  = pcf85363_rtc_ioctl,
 	.read_time	= pcf85363_rtc_read_time,
 	.set_time	= pcf85363_rtc_set_time,
 	.read_alarm	= pcf85363_rtc_read_alarm,
-- 
2.25.1