[RFC PATCH 03/14] watchdog: add driver for apple smc

[Atharva Tiwari]

Add a watchdog driver for the SMC on Intel Macs. It can
reset the machine if the system stops responding. It works
on both newer and older SMC versions.

Signed-off-by: Atharva Tiwari <atharvatiwarilinuxdev@xxxxxxxxx>
---
 drivers/mfd/macsmc-core.c     |  11 +++
 drivers/watchdog/Kconfig      |  11 +++
 drivers/watchdog/Makefile     |   2 +-
 drivers/watchdog/macsmc_wdt.c | 140 ++++++++++++++++++++++++++++++++++
 4 files changed, 163 insertions(+), 1 deletion(-)
 create mode 100644 drivers/watchdog/macsmc_wdt.c

diff --git a/drivers/mfd/macsmc-core.c b/drivers/mfd/macsmc-core.c
index b8905c834..1c1469828 100644
--- a/drivers/mfd/macsmc-core.c
+++ b/drivers/mfd/macsmc-core.c
@@ -33,6 +33,10 @@ static const struct mfd_cell apple_smc_acpi_rtc[] = {
 	MFD_CELL_NAME("macsmc-rtc"),
 };
 
+static const struct mfd_cell apple_smc_acpi_wdt[] = {
+	MFD_CELL_NAME("macsmc-wdt"),
+};
+
 int apple_smc_read(struct apple_smc *smc, smc_key key, void *buf, size_t size)
 {
 	guard(mutex)(&smc->mutex);
@@ -147,6 +151,13 @@ int apple_smc_probe(struct device *dev, const struct apple_smc_backend_ops *ops,
 				return ret;
 		}
 
+		if (apple_smc_key_exists(smc, SMC_KEY(NATJ))) {
+			ret = devm_mfd_add_devices(dev, -1, apple_smc_acpi_wdt,
+				ARRAY_SIZE(apple_smc_acpi_wdt), NULL, 0, NULL);
+			if (ret < 0)
+				return ret;
+		}
+
 	} else
 		ret = devm_mfd_add_devices(dev, -1, apple_smc_rtkit_devs,
 			ARRAY_SIZE(apple_smc_rtkit_devs), NULL, 0, NULL);
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index f7d0a0c2c..854ab772f 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1810,6 +1810,17 @@ config SIEMENS_SIMATIC_IPC_WDT
 	  To compile this driver as a module, choose M here: the module will be
 	  called simatic-ipc-wdt.
 
+config MACSMC_WDT
+	tristate "Apple SMC Watchdog"
+	depends on X86 && MACSMC_ACPI
+	select WATCHDOG_CORE
+	help
+	  This driver adds support for Watchdogs in Intel macs Using
+	  Apple SMC.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called macsmc_wdt.
+
 # M68K Architecture
 
 config M54xx_WATCHDOG
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index 9ac406677..f142a5d8d 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -158,7 +158,7 @@ obj-$(CONFIG_NIC7018_WDT) += nic7018_wdt.o
 obj-$(CONFIG_MLX_WDT) += mlx_wdt.o
 obj-$(CONFIG_KEEMBAY_WATCHDOG) += keembay_wdt.o
 obj-$(CONFIG_SIEMENS_SIMATIC_IPC_WDT) += simatic-ipc-wdt.o
-
+obj-$(CONFIG_MACSMC_WDT) += macsmc_wdt.o
 # M68K Architecture
 obj-$(CONFIG_M54xx_WATCHDOG) += m54xx_wdt.o
 
diff --git a/drivers/watchdog/macsmc_wdt.c b/drivers/watchdog/macsmc_wdt.c
new file mode 100644
index 000000000..38f68d0d8
--- /dev/null
+++ b/drivers/watchdog/macsmc_wdt.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Apple SMC Watchdog Driver
+ *
+ * Copyright (C) 2026 Atharva Tiwari <atharvatiwarilinuxdev@xxxxxxxxx>
+ */
+
+#include <linux/mfd/macsmc.h>
+#include <linux/platform_device.h>
+#include <linux/watchdog.h>
+
+#define WATCHDOG_TIMEOUT 60 /* 60 sec default timeout */
+
+static bool nowayout = WATCHDOG_NOWAYOUT;
+module_param(nowayout, bool, 0);
+MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started default="
+		 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
+
+static int timeout = WATCHDOG_TIMEOUT; /* in secounds */
+module_param(timeout, int, 0);
+MODULE_PARM_DESC(timeout,
+		 "Watchdog timeout in seconds. 1 <= timeout <= 255, default="
+		 __MODULE_STRING(WATCHDOG_TIMEOUT) ".");
+
+struct macsmc_wdt {
+	struct apple_smc *smc;
+	bool has_oswd; /* Newer version of watchdogs in macsmc */
+	struct watchdog_device wdd;
+};
+
+static int macsmc_wdt_set_timeout(struct watchdog_device *wdd, unsigned int timeout)
+{
+	struct macsmc_wdt *drv = watchdog_get_drvdata(wdd);
+	int ret;
+
+	if (timeout)
+		wdd->timeout = timeout;
+
+	if (drv->has_oswd) {
+		ret = apple_smc_write_u16(drv->smc, SMC_KEY(OSWD), (u16)(timeout << 8));
+		if (ret < 0)
+			return ret;
+	} else {
+		/*
+		 * NATJ = 2, makes the watchdog do force restart if NATi == 0
+		 * NATJ = 0, makes the watchdog do nothing if NATi == 0
+		 */
+		if (timeout == 0) {
+			ret = apple_smc_write_u16(drv->smc, SMC_KEY(NATJ), 0);
+			if (ret < 0)
+				return ret;
+		}
+		ret = apple_smc_write_u16(drv->smc, SMC_KEY(NATi), (u16)(timeout << 8));
+		if (ret < 0)
+			return ret;
+
+		if (timeout != 0) {
+			ret = apple_smc_write_u16(drv->smc, SMC_KEY(NATJ), 2);
+			if (ret < 0)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+static int macsmc_wdt_start(struct watchdog_device *wdd)
+{
+	return macsmc_wdt_set_timeout(wdd, wdd->timeout);
+}
+static int macsmc_wdt_stop(struct watchdog_device *wdd)
+{
+	return macsmc_wdt_set_timeout(wdd, 0);
+}
+
+static int macsmc_wdt_ping(struct watchdog_device *wdd)
+{
+	struct macsmc_wdt *drv = watchdog_get_drvdata(wdd);
+	int ret;
+
+	if (drv->has_oswd)
+		ret = apple_smc_write_u16(drv->smc, SMC_KEY(OSWD), (u16)(wdd->timeout << 8));
+	else
+		ret = apple_smc_write_u16(drv->smc, SMC_KEY(NATi), (u16)(wdd->timeout << 8));
+
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static const struct watchdog_ops macsmc_wdt_ops = {
+	.owner =	THIS_MODULE,
+	.start =	macsmc_wdt_start,
+	.stop  =	macsmc_wdt_stop,
+	.set_timeout =	macsmc_wdt_set_timeout,
+	.ping =	macsmc_wdt_ping,
+};
+
+static const struct watchdog_info macsmc_wdt_info = {
+	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING,
+	.identity = "Macsmc Watchdog timer",
+};
+
+static int macsmc_wdt_probe(struct platform_device *pdev)
+{
+	struct macsmc_wdt *drv;
+
+	drv = devm_kzalloc(&pdev->dev, sizeof(struct macsmc_wdt), GFP_KERNEL);
+	if (!drv)
+		return -ENOMEM;
+
+	drv->smc = dev_get_drvdata(pdev->dev.parent);
+	if (apple_smc_key_exists(drv->smc, SMC_KEY(OSWD)))
+		drv->has_oswd = true;
+	else
+		drv->has_oswd = false;
+
+	drv->wdd.ops = &macsmc_wdt_ops;
+	drv->wdd.info = &macsmc_wdt_info;
+	drv->wdd.min_timeout = 1;
+	drv->wdd.max_timeout = 255;
+	watchdog_init_timeout(&drv->wdd, timeout, &pdev->dev);
+	watchdog_set_nowayout(&drv->wdd, nowayout);
+	watchdog_set_drvdata(&drv->wdd, drv);
+
+	return devm_watchdog_register_device(&pdev->dev, &drv->wdd);
+}
+
+static struct platform_driver macsmc_wdt_driver = {
+	.probe = macsmc_wdt_probe,
+	.driver = {
+		.name = "macsmc-wdt"
+	},
+};
+module_platform_driver(macsmc_wdt_driver);
+
+MODULE_AUTHOR("Atharva Tiwari <atharvatiwarilinuxdev@xxxxxxxxx>");
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_DESCRIPTION("Apple SMC Watchdog Driver");
+MODULE_ALIAS("platform:macsmc-wdt");
-- 
2.55.0