Subject: watchdog: add Hasivo MCU watchdog driver
Hardware watchdog driver for the external management MCU found on
-Hasivo / Horaco network switches, reachable over I2C. Without periodic
-keepalive the MCU resets the board every ~3 minutes.
+Hasivo / Horaco network switches. The watchdog is a sub-function of the
+Hasivo management MCU (hasivo,stc8-mfd): it is a child of that MFD
+and reaches the MCU through the parent's shared regmap, so the watchdog
+and the hwmon sensor can share the single I2C address the MCU occupies.
-The driver arms the MCU at probe and registers a struct watchdog_device
-with WDOG_HW_RUNNING so the watchdog core feeds the chip via a kernel
-timer until userspace opens the watchdog node. Timeout is fixed at 15s;
-the hardware threshold is baked into MCU firmware and is not
-software-configurable.
+Without periodic keepalive the MCU resets the board. The driver arms the
+MCU at probe and registers a struct watchdog_device with WDOG_HW_RUNNING
+so the watchdog core feeds the chip via a kernel timer until userspace
+opens the watchdog node. Timeout is fixed at 15s; the hardware threshold
+is baked into MCU firmware and is not software-configurable.
Signed-off-by: Carlo Szelinsky <github@szelinsky.de>
Signed-off-by: Manuel Stocker <mensi@mensi.ch>
---
--- /dev/null
+++ b/Documentation/devicetree/bindings/watchdog/hasivo,mcu-wdt.yaml
-@@ -0,0 +1,45 @@
+@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+ - Manuel Stocker <mensi@mensi.ch>
+
+description: |
-+ Management microcontroller found on Hasivo and Horaco network switches,
-+ exposed on the system I2C bus. Provides a hardware watchdog that must be
-+ armed and periodically retriggered by the host via I2C writes.
++ Watchdog sub-function of the Hasivo / Horaco management microcontroller
++ found on these network switches (see hasivo,stc8-mfd). It must be armed
++ and periodically retriggered by the host through the parent MFD's
++ register map, otherwise the MCU resets the board.
+
+allOf:
+ - $ref: watchdog.yaml#
+ compatible:
+ const: hasivo,mcu-wdt
+
-+ reg:
-+ maxItems: 1
-+
+required:
+ - compatible
-+ - reg
+
+unevaluatedProperties: false
+
+ #address-cells = <1>;
+ #size-cells = <0>;
+
-+ watchdog@6f {
-+ compatible = "hasivo,mcu-wdt";
++ mcu@6f {
++ compatible = "hasivo,stc8-mfd", "syscon";
+ reg = <0x6f>;
++
++ watchdog {
++ compatible = "hasivo,mcu-wdt";
++ };
+ };
+ };
+...
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
-@@ -302,6 +302,18 @@ config MENF21BMC_WATCHDOG
+@@ -302,6 +302,20 @@ config MENF21BMC_WATCHDOG
This driver can also be built as a module. If so the module
will be called menf21bmc_wdt.
+config HASIVO_MCU_WATCHDOG
+ tristate "Hasivo MCU Watchdog"
-+ depends on I2C
++ depends on MFD_HASIVO_STC8 && OF
+ select WATCHDOG_CORE
+ help
+ Hardware watchdog driver for the external management MCU found
-+ on Hasivo and Horaco network switches, reachable over I2C. The
-+ MCU resets the board unless it is periodically retriggered.
++ on Hasivo and Horaco network switches. It is a sub-function of
++ the Hasivo management MCU (hasivo,stc8-mfd) and is reached
++ through that MFD's register map. The MCU resets the board unless
++ it is periodically retriggered.
+
+ This driver can also be built as a module. If so the module
+ will be called hasivo-mcu-wdt.
+ * Hasivo MCU Watchdog Driver
+ *
+ * Hardware watchdog driver for the external management MCU found on
-+ * Hasivo / Horaco network switches. Communicates over I2C.
++ * Hasivo / Horaco network switches. The watchdog is a sub-function of
++ * the Hasivo STC8-style management chip (hasivo,stc8-mfd); all register
++ * access goes through the parent MFD's regmap.
+ *
+ * Protocol reverse-engineered from the stock firmware ("imi" daemon +
+ * i2c-poe.ko kernel module):
+ * Copyright (C) 2026 Carlo Szelinsky <github@szelinsky.de>
+ */
+
-+#include <linux/i2c.h>
++#include <linux/mfd/syscon.h>
+#include <linux/module.h>
++#include <linux/of.h>
++#include <linux/platform_device.h>
++#include <linux/regmap.h>
+#include <linux/watchdog.h>
+
+#define HASIVO_REG_WDT_UNLOCK 0x09
+#define HASIVO_WDT_TIMEOUT 15
+
+struct hasivo_mcu {
-+ struct i2c_client *client;
++ struct regmap *regmap;
+ struct watchdog_device wdd;
+};
+
+{
+ int ret;
+
-+ ret = i2c_smbus_write_byte_data(mcu->client, HASIVO_REG_WDT_UNLOCK,
-+ HASIVO_WDT_UNLOCK_MAGIC);
++ ret = regmap_write(mcu->regmap, HASIVO_REG_WDT_UNLOCK,
++ HASIVO_WDT_UNLOCK_MAGIC);
+ if (ret)
+ return ret;
+
-+ return i2c_smbus_write_byte_data(mcu->client, HASIVO_REG_WDT_CMD, cmd);
++ return regmap_write(mcu->regmap, HASIVO_REG_WDT_CMD, cmd);
+}
+
+static int hasivo_mcu_wdt_start(struct watchdog_device *wdd)
+{
+ struct hasivo_mcu *mcu = watchdog_get_drvdata(wdd);
+
-+ return i2c_smbus_write_byte_data(mcu->client,
-+ HASIVO_REG_WDT_KEEPALIVE,
-+ HASIVO_WDT_KEEPALIVE_MAGIC);
++ return regmap_write(mcu->regmap, HASIVO_REG_WDT_KEEPALIVE,
++ HASIVO_WDT_KEEPALIVE_MAGIC);
+}
+
+static const struct watchdog_info hasivo_mcu_wdt_info = {
+ .ping = hasivo_mcu_wdt_ping,
+};
+
-+static int hasivo_mcu_probe(struct i2c_client *client)
++static int hasivo_mcu_wdt_probe(struct platform_device *pdev)
+{
-+ struct device *dev = &client->dev;
++ struct device *dev = &pdev->dev;
+ struct hasivo_mcu *mcu;
+ int ret;
+
+ if (!mcu)
+ return -ENOMEM;
+
-+ mcu->client = client;
++ mcu->regmap = syscon_node_to_regmap(dev_of_node(dev->parent));
++ if (IS_ERR(mcu->regmap))
++ return dev_err_probe(dev, PTR_ERR(mcu->regmap),
++ "failed to get parent regmap\n");
+
+ /*
+ * Arm the watchdog. The stock bootloader normally leaves it
+ if (ret)
+ return dev_err_probe(dev, ret, "failed to arm watchdog\n");
+
-+ ret = i2c_smbus_write_byte_data(client, HASIVO_REG_WDT_KEEPALIVE,
-+ HASIVO_WDT_KEEPALIVE_MAGIC);
++ ret = regmap_write(mcu->regmap, HASIVO_REG_WDT_KEEPALIVE,
++ HASIVO_WDT_KEEPALIVE_MAGIC);
+ if (ret)
+ return dev_err_probe(dev, ret,
+ "initial watchdog ping failed\n");
+ return dev_err_probe(dev, ret,
+ "failed to register watchdog\n");
+
-+ dev_info(dev, "Hasivo MCU watchdog armed at 0x%02x (timeout %us)\n",
-+ client->addr, mcu->wdd.timeout);
++ dev_info(dev, "Hasivo MCU watchdog armed (timeout %us)\n",
++ mcu->wdd.timeout);
+
+ return 0;
+}
+};
+MODULE_DEVICE_TABLE(of, hasivo_mcu_of_match);
+
-+static const struct i2c_device_id hasivo_mcu_id[] = {
-+ { "hasivo-mcu-wdt" },
-+ { }
-+};
-+MODULE_DEVICE_TABLE(i2c, hasivo_mcu_id);
-+
-+static struct i2c_driver hasivo_mcu_driver = {
++static struct platform_driver hasivo_mcu_driver = {
+ .driver = {
+ .name = "hasivo-mcu-wdt",
+ .of_match_table = hasivo_mcu_of_match,
+ },
-+ .probe = hasivo_mcu_probe,
-+ .id_table = hasivo_mcu_id,
++ .probe = hasivo_mcu_wdt_probe,
+};
-+module_i2c_driver(hasivo_mcu_driver);
++module_platform_driver(hasivo_mcu_driver);
+
+MODULE_DESCRIPTION("Hasivo MCU Watchdog Driver");
+MODULE_LICENSE("GPL");
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