[PATCH v2] watchdog: sunxi_wdt: preserve boot-enabled watchdog

[James Hilliard <james.hilliard1@gmail.com>]

sunxi_wdt_probe() unconditionally stops the watchdog even when firmware
left it running. This opens an unprotected interval during boot and
prevents CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED from taking over the active
watchdog.

Detect an enabled watchdog and decode its programmed interval. Preserve
representable timeouts, and round the 0.5-second interval up to the
minimum representable one-second timeout. Use the configured timeout for
reserved interval encodings. Set the Linux reset mode and ping the
watchdog without clearing its enable bit, then mark it hardware-running
before registration so the watchdog core services it until userspace
takes control. Leave disabled watchdogs untouched.

Fixes: d00680ed0026 ("watchdog: sunxi: New watchdog driver for Allwinner A10/A13")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
Changes v1 -> v2:
  - Use one second for the boot-enabled 0.5-second interval instead of
    falling back to the configured timeout.  (suggested by Guenter Roeck)
  - Leave an already-disabled watchdog untouched.  (suggested by Guenter Roeck)
---
 drivers/watchdog/sunxi_wdt.c | 45 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/sunxi_wdt.c b/drivers/watchdog/sunxi_wdt.c
index b6c761acc3de..3db34524ed13 100644
--- a/drivers/watchdog/sunxi_wdt.c
+++ b/drivers/watchdog/sunxi_wdt.c
@@ -128,6 +128,38 @@ static int sunxi_wdt_ping(struct watchdog_device *wdt_dev)
 	return 0;
 }
 
+static bool sunxi_wdt_is_running(struct watchdog_device *wdt_dev)
+{
+	struct sunxi_wdt_dev *sunxi_wdt = watchdog_get_drvdata(wdt_dev);
+	const struct sunxi_wdt_reg *regs = sunxi_wdt->wdt_regs;
+
+	return readl(sunxi_wdt->wdt_base + regs->wdt_mode) & WDT_MODE_EN;
+}
+
+static unsigned int sunxi_wdt_get_timeout(struct watchdog_device *wdt_dev)
+{
+	struct sunxi_wdt_dev *sunxi_wdt = watchdog_get_drvdata(wdt_dev);
+	const struct sunxi_wdt_reg *regs = sunxi_wdt->wdt_regs;
+	unsigned int timeout;
+	u32 interval;
+
+	interval = readl(sunxi_wdt->wdt_base + regs->wdt_mode);
+	interval >>= regs->wdt_timeout_shift;
+	interval &= WDT_TIMEOUT_MASK;
+	/* Round the 0.5-second interval up to the minimum representable timeout. */
+	if (!interval)
+		return WDT_MIN_TIMEOUT;
+
+	for (timeout = WDT_MIN_TIMEOUT;
+	     timeout < ARRAY_SIZE(wdt_timeout_map); timeout++) {
+		if (wdt_timeout_map[timeout] == interval)
+			return timeout;
+	}
+
+	/* Reserved interval encoding. */
+	return 0;
+}
+
 static int sunxi_wdt_set_timeout(struct watchdog_device *wdt_dev,
 		unsigned int timeout)
 {
@@ -259,6 +291,7 @@ static int sunxi_wdt_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct sunxi_wdt_dev *sunxi_wdt;
+	unsigned int running_timeout;
 	int err;
 
 	sunxi_wdt = devm_kzalloc(dev, sizeof(*sunxi_wdt), GFP_KERNEL);
@@ -286,7 +319,17 @@ static int sunxi_wdt_probe(struct platform_device *pdev)
 
 	watchdog_set_drvdata(&sunxi_wdt->wdt_dev, sunxi_wdt);
 
-	sunxi_wdt_stop(&sunxi_wdt->wdt_dev);
+	if (sunxi_wdt_is_running(&sunxi_wdt->wdt_dev)) {
+		running_timeout = sunxi_wdt_get_timeout(&sunxi_wdt->wdt_dev);
+		if (running_timeout)
+			sunxi_wdt->wdt_dev.timeout = running_timeout;
+
+		err = sunxi_wdt_start(&sunxi_wdt->wdt_dev);
+		if (err)
+			return err;
+
+		set_bit(WDOG_HW_RUNNING, &sunxi_wdt->wdt_dev.status);
+	}
 
 	watchdog_stop_on_reboot(&sunxi_wdt->wdt_dev);
 	err = devm_watchdog_register_device(dev, &sunxi_wdt->wdt_dev);

---
base-commit: 1b78070aaef63512688aebfbc82365ef9d6660f1
change-id: 20260827-submit-sunxi-wdt-boot-enabled-v1-94cd6be885d2

Best regards,
--  
James Hilliard <james.hilliard1@gmail.com>