linux-kernel - [PATCH]: watchdog: Allow watchdog to remain enabled after probe

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Message-Id: <20250206093956.46593-1-regis.dargent@gmail.com>
Date: Thu,  6 Feb 2025 10:39:56 +0100
From: Regis Dargent <regis.dargent@...il.com>
To: linux-arm-kernel@...ts.infradead.org,
	linux-sunxi@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>,
	Guenter Roeck <linux@...ck-us.net>,
	linux-watchdog@...r.kernel.org,
	Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>
Subject: [PATCH]: watchdog: Allow watchdog to remain enabled after probe

---
The sunxi_wdt watchdog unconditionally stops the watchdog during probe (on my Allwinner H616).

What I want to achieve with this patch is to start the watchdog in the bootloader (either manually or automatically), then boot Linux.
The watchdog is about 16sec timeout maximum, while the full boot to userland lasts about 90sec, and I want the board to reset if, eg.
the rootfs cannot be mounted. So I need the watchdog to be handled by the kernel during boot (which it can do pretty well).

The thing is, the current driver stops the watchdog during probe, so it does not run during boot, and it also does not manages the "status"
field, so the kernel would know that it must handle the HW watchdog.
This avoids automatic reboot in case a problem occurs during boot (and for example handling in the bootloader).

The driver should detect if the HW watchdog is already running during probe and set its appropriate status bit to allow the kernel to handle the watchdog pings itself.
The call to sunxi_wdt_start/stop allows for proper driver and device configuration.
By default, the kernel will then ping the HW watchdog at apropriate frequency, but the user can have it stop after a time with open_timeout parameter.

 drivers/watchdog/sunxi_wdt.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/sunxi_wdt.c b/drivers/watchdog/sunxi_wdt.c
index b85354a99582..20fe7da445ea 100644
--- a/drivers/watchdog/sunxi_wdt.c
+++ b/drivers/watchdog/sunxi_wdt.c
@@ -192,6 +192,16 @@ static int sunxi_wdt_start(struct watchdog_device *wdt_dev)
 	return 0;
 }

+static int sunxi_wdt_enabled(struct sunxi_wdt_dev *wdt)
+{
+	u32 reg;
+	void __iomem *wdt_base = wdt->wdt_base;
+	const struct sunxi_wdt_reg *regs = wdt->wdt_regs;
+
+	reg = readl(wdt_base + regs->wdt_mode);
+	return (reg & WDT_MODE_EN);
+}
+
 static const struct watchdog_info sunxi_wdt_info = {
 	.identity	= DRV_NAME,
 	.options	= WDIOF_SETTIMEOUT |
@@ -268,6 +278,11 @@ static int sunxi_wdt_probe(struct platform_device *pdev)
 	sunxi_wdt->wdt_dev.max_timeout = WDT_MAX_TIMEOUT;
 	sunxi_wdt->wdt_dev.min_timeout = WDT_MIN_TIMEOUT;
 	sunxi_wdt->wdt_dev.parent = dev;
+	if (sunxi_wdt_enabled(sunxi_wdt)) {
+		set_bit(WDOG_HW_RUNNING, &sunxi_wdt->wdt_dev.status);
+	} else {
+		clear_bit(WDOG_HW_RUNNING, &sunxi_wdt->wdt_dev.status);
+	}

 	watchdog_init_timeout(&sunxi_wdt->wdt_dev, timeout, dev);
 	watchdog_set_nowayout(&sunxi_wdt->wdt_dev, nowayout);
@@ -275,7 +290,10 @@ 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 (watchdog_hw_running(&sunxi_wdt->wdt_dev))
+		sunxi_wdt_start(&sunxi_wdt->wdt_dev);
+	else
+		sunxi_wdt_stop(&sunxi_wdt->wdt_dev);

 	watchdog_stop_on_reboot(&sunxi_wdt->wdt_dev);
 	err = devm_watchdog_register_device(dev, &sunxi_wdt->wdt_dev);
-- 
2.25.1