Add watchdog driver for the Aaeon SRG-IMX8P embedded controller.
This driver provides system monitoring and recovery capabilities
through the MCU's watchdog timer.

The watchdog supports start, stop, and ping operations with a maximum
hardware heartbeat of 25 seconds and a default timeout of 240 seconds.

Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 MAINTAINERS                      |   1 +
 drivers/watchdog/Kconfig         |  10 +++
 drivers/watchdog/Makefile        |   1 +
 drivers/watchdog/aaeon_mcu_wdt.c | 134 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 146 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 2538f8c4bc1482b139e18243a68f0a21b9be3704..7b92af42c9fdc17a69a4e7a2fe50f9e199c8b144 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -193,6 +193,7 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
 F:	drivers/gpio/gpio-aaeon-mcu.c
 F:	drivers/mfd/aaeon-mcu.c
+F:	drivers/watchdog/aaeon_mcu_wdt.c
 F:	include/linux/mfd/aaeon-mcu.h
 
 AAEON UPBOARD FPGA MFD DRIVER
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index d3b9df7d466b0b7215ee87b3040811d44ee53d2a..da54e6a641d7af343e4f0ae84f96f150979f8348 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -168,6 +168,16 @@ config SOFT_WATCHDOG_PRETIMEOUT
 	  watchdog. Be aware that governors might affect the watchdog because it
 	  is purely software, e.g. the panic governor will stall it!
 
+config AAEON_MCU_WATCHDOG
+	tristate "Aaeon MCU Watchdog"
+	depends on MFD_AAEON_MCU
+	select WATCHDOG_CORE
+	help
+	  Select this option to enable watchdog timer support for the Aaeon
+	  SRG-IMX8P onboard microcontroller (MCU). This driver provides
+	  watchdog functionality through the MCU, allowing system monitoring
+	  and automatic recovery from system hangs.
+
 config BD957XMUF_WATCHDOG
 	tristate "ROHM BD9576MUF and BD9573MUF PMIC Watchdog"
 	depends on MFD_ROHM_BD957XMUF
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index ba52099b125398a32f80dad23317e223cc4af028..2deec425d3eafb6b208e061fda9f216f4baa8ecc 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_USBPCWATCHDOG) += pcwd_usb.o
 # ALPHA Architecture
 
 # ARM Architecture
+obj-$(CONFIG_AAEON_MCU_WATCHDOG) += aaeon_mcu_wdt.o
 obj-$(CONFIG_ARM_SP805_WATCHDOG) += sp805_wdt.o
 obj-$(CONFIG_ARM_SBSA_WATCHDOG) += sbsa_gwdt.o
 obj-$(CONFIG_ARMADA_37XX_WATCHDOG) += armada_37xx_wdt.o
diff --git a/drivers/watchdog/aaeon_mcu_wdt.c b/drivers/watchdog/aaeon_mcu_wdt.c
new file mode 100644
index 0000000000000000000000000000000000000000..f01571cf0036d252f9bebd3a9d6a1c2e7a83e42c
--- /dev/null
+++ b/drivers/watchdog/aaeon_mcu_wdt.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Aaeon MCU Watchdog driver
+ *
+ * Copyright (C) 2025 Bootlin
+ * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+ * Author: Thomas Perrot <thomas.perrot@bootlin.com>
+ */
+
+#include <linux/mfd/aaeon-mcu.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/watchdog.h>
+
+#define AAEON_MCU_CONTROL_WDT	0x63
+#define AAEON_MCU_PING_WDT	0x73
+
+#define AAEON_MCU_WDT_TIMEOUT         240
+#define AAEON_MCU_WDT_HEARTBEAT_MS    25000
+
+struct aaeon_mcu_wdt {
+	struct watchdog_device wdt;
+	struct regmap *regmap;
+};
+
+static int aaeon_mcu_wdt_cmd(struct aaeon_mcu_wdt *data, u8 opcode, u8 arg)
+{
+	/* The MCU always sends a response byte after each command; discard it. */
+	return regmap_write(data->regmap, AAEON_MCU_REG(opcode, arg), 0);
+}
+
+static int aaeon_mcu_wdt_start(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT, 0x01);
+}
+
+static int aaeon_mcu_wdt_status(struct watchdog_device *wdt, bool *enabled)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+	unsigned int rsp;
+	int ret;
+
+	ret = regmap_read(data->regmap,
+			  AAEON_MCU_REG(AAEON_MCU_CONTROL_WDT, 0x02),
+			  &rsp);
+	if (ret)
+		return ret;
+
+	*enabled = rsp == 0x01;
+	return 0;
+}
+
+static int aaeon_mcu_wdt_stop(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT, 0x00);
+}
+
+static int aaeon_mcu_wdt_ping(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_PING_WDT, 0x00);
+}
+
+static const struct watchdog_info aaeon_mcu_wdt_info = {
+	.identity	= "Aaeon MCU Watchdog",
+	.options	= WDIOF_KEEPALIVEPING
+};
+
+static const struct watchdog_ops aaeon_mcu_wdt_ops = {
+	.owner		= THIS_MODULE,
+	.start		= aaeon_mcu_wdt_start,
+	.stop		= aaeon_mcu_wdt_stop,
+	.ping		= aaeon_mcu_wdt_ping,
+};
+
+static int aaeon_mcu_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct watchdog_device *wdt;
+	struct aaeon_mcu_wdt *data;
+	bool enabled;
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = dev_get_regmap(dev->parent, NULL);
+	if (!data->regmap)
+		return -ENODEV;
+
+	wdt = &data->wdt;
+	wdt->parent = dev;
+	wdt->info = &aaeon_mcu_wdt_info;
+	wdt->ops = &aaeon_mcu_wdt_ops;
+	/*
+	 * The MCU firmware has a fixed hardware timeout of 25 seconds that
+	 * cannot be changed. The watchdog core will handle automatic pinging
+	 * to support longer timeouts. The software timeout of 240 seconds is
+	 * chosen arbitrarily as a reasonable value and is not user-configurable.
+	 */
+	wdt->timeout = AAEON_MCU_WDT_TIMEOUT;
+	wdt->max_hw_heartbeat_ms = AAEON_MCU_WDT_HEARTBEAT_MS;
+
+	watchdog_set_drvdata(wdt, data);
+
+	ret = aaeon_mcu_wdt_status(wdt, &enabled);
+	if (ret)
+		return ret;
+
+	if (enabled)
+		set_bit(WDOG_HW_RUNNING, &wdt->status);
+
+	return devm_watchdog_register_device(dev, wdt);
+}
+
+static struct platform_driver aaeon_mcu_wdt_driver = {
+	.driver		= {
+		.name	= "aaeon-mcu-wdt",
+	},
+	.probe		= aaeon_mcu_wdt_probe,
+};
+
+module_platform_driver(aaeon_mcu_wdt_driver);
+
+MODULE_DESCRIPTION("Aaeon MCU Watchdog Driver");
+MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
+MODULE_LICENSE("GPL");

-- 
2.53.0