linux-kernel - [PATCH v2] clocksource: timer-tegra186: Enable WDT at probe

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Message-ID: <20250703110415.232741-1-kkartik@nvidia.com>
Date: Thu, 3 Jul 2025 16:34:15 +0530
From: Kartik Rajput <kkartik@...dia.com>
To: <daniel.lezcano@...aro.org>, <tglx@...utronix.de>,
	<thierry.reding@...il.com>, <jonathanh@...dia.com>,
	<linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>
CC: <kkartik@...dia.com>
Subject: [PATCH v2] clocksource: timer-tegra186: Enable WDT at probe

Currently, if the system crashes or hangs during kernel boot before
userspace initializes and configures the watchdog timer, then the
watchdog won’t be able to recover the system as it’s not running. This
becomes crucial during an over-the-air update, where if the newly
updated kernel crashes on boot, the watchdog is needed to reset the
device and boot into an alternative system partition. If the watchdog
is disabled in such scenarios, it can lead to the system getting
bricked.

Enable the WDT during driver probe to allow recovery from any crash/hang
seen during early kernel boot. Also, disable interrupts once userspace
starts pinging the watchdog.

Signed-off-by: Kartik Rajput <kkartik@...dia.com>
---
 drivers/clocksource/timer-tegra186.c | 46 ++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/drivers/clocksource/timer-tegra186.c b/drivers/clocksource/timer-tegra186.c
index e5394f98a02e..bb16a119d55f 100644
--- a/drivers/clocksource/timer-tegra186.c
+++ b/drivers/clocksource/timer-tegra186.c
@@ -57,6 +57,8 @@
 #define WDTUR 0x00c
 #define  WDTUR_UNLOCK_PATTERN 0x0000c45a
 
+#define WDT_DEFAULT_TIMEOUT 120
+
 struct tegra186_timer_soc {
 	unsigned int num_timers;
 	unsigned int num_wdts;
@@ -74,6 +76,7 @@ struct tegra186_wdt {
 
 	void __iomem *regs;
 	unsigned int index;
+	bool enable_irq;
 	bool locked;
 
 	struct tegra186_tmr *tmr;
@@ -174,6 +177,16 @@ static void tegra186_wdt_enable(struct tegra186_wdt *wdt)
 		value &= ~WDTCR_PERIOD_MASK;
 		value |= WDTCR_PERIOD(1);
 
+		/*
+		 * If enable_irq is set then enable the watchdog IRQ for kernel
+		 * petting, otherwise userspace is responsible for petting the
+		 * watchdog.
+		 */
+		if (wdt->enable_irq)
+			value |= WDTCR_LOCAL_INT_ENABLE;
+		else
+			value &= ~WDTCR_LOCAL_INT_ENABLE;
+
 		/* enable system POR reset */
 		value |= WDTCR_SYSTEM_POR_RESET_ENABLE;
 
@@ -205,6 +218,10 @@ static int tegra186_wdt_ping(struct watchdog_device *wdd)
 {
 	struct tegra186_wdt *wdt = to_tegra186_wdt(wdd);
 
+	/* Disable the watchdog IRQ now userspace is taking over. */
+	if (wdt->enable_irq)
+		wdt->enable_irq = false;
+
 	tegra186_wdt_disable(wdt);
 	tegra186_wdt_enable(wdt);
 
@@ -315,6 +332,8 @@ static struct tegra186_wdt *tegra186_wdt_create(struct tegra186_timer *tegra,
 	if (value & WDTCR_LOCAL_INT_ENABLE)
 		wdt->locked = true;
 
+	wdt->enable_irq = true;
+
 	source = value & WDTCR_TIMER_SOURCE_MASK;
 
 	wdt->tmr = tegra186_tmr_create(tegra, source);
@@ -339,6 +358,13 @@ static struct tegra186_wdt *tegra186_wdt_create(struct tegra186_timer *tegra,
 		return ERR_PTR(err);
 	}
 
+	/*
+	 * Start the watchdog to recover the system if it crashes before
+	 * userspace initialize the WDT.
+	 */
+	tegra186_wdt_set_timeout(&wdt->base, WDT_DEFAULT_TIMEOUT);
+	tegra186_wdt_start(&wdt->base);
+
 	return wdt;
 }
 
@@ -415,10 +441,21 @@ static int tegra186_timer_usec_init(struct tegra186_timer *tegra)
 	return clocksource_register_hz(&tegra->usec, USEC_PER_SEC);
 }
 
+static irqreturn_t tegra186_timer_irq(int irq, void *data)
+{
+	struct tegra186_timer *tegra = data;
+
+	tegra186_wdt_disable(tegra->wdt);
+	tegra186_wdt_enable(tegra->wdt);
+
+	return IRQ_HANDLED;
+}
+
 static int tegra186_timer_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct tegra186_timer *tegra;
+	unsigned int irq;
 	int err;
 
 	tegra = devm_kzalloc(dev, sizeof(*tegra), GFP_KERNEL);
@@ -437,6 +474,15 @@ static int tegra186_timer_probe(struct platform_device *pdev)
 	if (err < 0)
 		return err;
 
+	irq = err;
+
+	err = devm_request_irq(dev, irq, tegra186_timer_irq, 0,
+			       "tegra186-timer", tegra);
+	if (err < 0) {
+		dev_err(dev, "failed to request IRQ#%u: %d\n", irq, err);
+		return err;
+	}
+
 	/* create a watchdog using a preconfigured timer */
 	tegra->wdt = tegra186_wdt_create(tegra, 0);
 	if (IS_ERR(tegra->wdt)) {
-- 
2.43.0