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

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On Wed, May 21, 2025 at 05:00:12PM +0400, Alexey Charkov wrote:
> 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.

Module is not supported by the timers. That will change in a very near
future but unloading won't be supported, you should consider tying the
wdt life cycle with the subsystem it is connected to.

>  # 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
> 

-- 

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