[PATCH v5 4/4] watchdog: Add support for VIA/WonderMedia SoC watchdog functionality

[Alexey Charkov <alchark@gmail.com>]

VIA/WonderMedia SoCs can use their system timer's first channel as a
watchdog device which will reset the system if the clocksource counter
matches the value given in its match register 0 and if the watchdog
function is enabled.

Since the watchdog function is tightly coupled to the timer itself, it
is implemented as an auxiliary device of the timer device

Signed-off-by: Alexey Charkov <alchark@gmail.com>
---
 MAINTAINERS                   |  1 +
 drivers/watchdog/Kconfig      | 15 ++++++++
 drivers/watchdog/Makefile     |  1 +
 drivers/watchdog/vt8500-wdt.c | 88 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 105 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 5362095240627f613638197fda275db6edc16cf7..97d1842625dbdf7fdca3556260662dab469ed091 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3447,6 +3447,7 @@ F:	drivers/tty/serial/vt8500_serial.c
 F:	drivers/video/fbdev/vt8500lcdfb.*
 F:	drivers/video/fbdev/wm8505fb*
 F:	drivers/video/fbdev/wmt_ge_rops.*
+F:	drivers/watchdog/vt8500-wdt.c
 F:	include/linux/vt8500-timer.h
 
 ARM/ZYNQ ARCHITECTURE
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 0d8d37f712e8cfb4bf8156853baa13c23a57d6d9..2e59303306feba7e15a015c2fce25b1290dc4cbc 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1115,6 +1115,21 @@ config SUNPLUS_WATCHDOG
 	  To compile this driver as a module, choose M here: the
 	  module will be called sunplus_wdt.
 
+config VT8500_WATCHDOG
+	tristate "VIA/WonderMedia VT8500 watchdog support"
+	depends on ARCH_VT8500 || COMPILE_TEST
+	select WATCHDOG_CORE
+	select AUXILIARY_BUS
+	help
+	  VIA/WonderMedia SoCs can use their system timer as a hardware
+	  watchdog, as long as the first timer channel is free from other
+	  uses and respective function is enabled in its registers. To
+	  make use of it, say Y here and ensure that the device tree
+	  lists at least two interrupts for the VT8500 timer device.
+
+	  To compile this driver as a module, choose M here.
+	  The module will be called vt8500-wdt.
+
 # X86 (i386 + ia64 + x86_64) Architecture
 
 config ACQUIRE_WDT
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index c9482904bf870a085c7fce2a439ac5089b6e6fee..3072786bf226c357102be3734fe6e701f753d45b 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -101,6 +101,7 @@ obj-$(CONFIG_MSC313E_WATCHDOG) += msc313e_wdt.o
 obj-$(CONFIG_APPLE_WATCHDOG) += apple_wdt.o
 obj-$(CONFIG_SUNPLUS_WATCHDOG) += sunplus_wdt.o
 obj-$(CONFIG_MARVELL_GTI_WDT) += marvell_gti_wdt.o
+obj-$(CONFIG_VT8500_WATCHDOG) += vt8500-wdt.o
 
 # X86 (i386 + ia64 + x86_64) Architecture
 obj-$(CONFIG_ACQUIRE_WDT) += acquirewdt.o
diff --git a/drivers/watchdog/vt8500-wdt.c b/drivers/watchdog/vt8500-wdt.c
new file mode 100644
index 0000000000000000000000000000000000000000..a47ee714e7c0172e89a31b0d6c064fff338bd5b6
--- /dev/null
+++ b/drivers/watchdog/vt8500-wdt.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2025 Alexey Charkov <alchark@gmail.com */
+
+#include <linux/auxiliary_bus.h>
+#include <linux/container_of.h>
+#include <linux/io.h>
+#include <linux/limits.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/watchdog.h>
+#include <linux/vt8500-timer.h>
+
+static int vt8500_watchdog_start(struct watchdog_device *wdd)
+{
+	struct vt8500_wdt_info *info = watchdog_get_drvdata(wdd);
+	u32 deadline = min(wdd->timeout * 1000, wdd->max_hw_heartbeat_ms);
+
+	/* The deadline is matched against the hardware clocksource counter,
+	 * which is a u32 value incrementing at VT8500_TIMER_HZ and continuing
+	 * past wraparound. When the return value of timer_next is greater than
+	 * U32_MAX then the match should occur after the hardware counter wraps
+	 * around, thus we take only the lower 32 bits of timer_next return val
+	 */
+	deadline = info->timer_next((u64)deadline * (VT8500_TIMER_HZ / 1000));
+	writel(deadline, info->wdt_match);
+	writel(1, info->wdt_en);
+	return 0;
+}
+
+static int vt8500_watchdog_stop(struct watchdog_device *wdd)
+{
+	struct vt8500_wdt_info *info = watchdog_get_drvdata(wdd);
+
+	writel(0, info->wdt_en);
+	return 0;
+}
+
+static const struct watchdog_ops vt8500_watchdog_ops = {
+	.start			= vt8500_watchdog_start,
+	.stop			= vt8500_watchdog_stop,
+};
+
+static const struct watchdog_info vt8500_watchdog_info = {
+	.identity		= "VIA VT8500 watchdog",
+	.options		= WDIOF_MAGICCLOSE |
+				  WDIOF_KEEPALIVEPING |
+				  WDIOF_SETTIMEOUT,
+};
+
+static int vt8500_wdt_probe(struct auxiliary_device *auxdev,
+			    const struct auxiliary_device_id *id)
+{
+	struct vt8500_wdt_info *info;
+	struct watchdog_device *wdd;
+
+	wdd = devm_kzalloc(&auxdev->dev, sizeof(*wdd), GFP_KERNEL);
+	if (!wdd)
+		return -ENOMEM;
+
+	wdd->info = &vt8500_watchdog_info;
+	wdd->ops = &vt8500_watchdog_ops;
+	wdd->max_hw_heartbeat_ms = U32_MAX / (VT8500_TIMER_HZ / 1000);
+	wdd->parent = &auxdev->dev;
+
+	info = container_of(auxdev, struct vt8500_wdt_info, auxdev);
+	watchdog_set_drvdata(wdd, info);
+
+	return devm_watchdog_register_device(&auxdev->dev, wdd);
+}
+
+static const struct auxiliary_device_id vt8500_wdt_ids[] = {
+	{ .name = "timer_vt8500.vt8500-wdt" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(auxiliary, my_auxiliary_id_table);
+
+static struct auxiliary_driver vt8500_wdt_driver = {
+	.name =	"vt8500-wdt",
+	.probe = vt8500_wdt_probe,
+	.id_table = vt8500_wdt_ids,
+};
+module_auxiliary_driver(vt8500_wdt_driver);
+
+MODULE_AUTHOR("Alexey Charkov <alchark@gmail.com>");
+MODULE_DESCRIPTION("Driver for the VIA VT8500 watchdog timer");
+MODULE_LICENSE("GPL");

-- 
2.49.0