[PATCH 1/2] watchdog: add gpio watchdog driver

[Stefan Roese]

On 10.05.21 17:47, Rasmus Villemoes wrote:
> A rather common kind of external watchdog circuit is one that is kept
> alive by toggling a gpio. Add a driver for handling such a watchdog.
> 
> The compatible string is probably a little odd as it has nothing to do
> with linux per se - however, I chose that to make .dts snippets
> reusable between device trees used with U-Boot and linux, and this is
> the (only) compatible string that linux' corresponding driver and DT
> binding accepts. I have asked whether one should/could add "wdt-gpio"
> to that binding, but the answer was no:
> 
>    https://lore.kernel.org/lkml/CAL_JsqKEGaFpiFV_oAtE+S_bnHkg4qry+bhx2EDs=NSbVf_giA@mail.gmail.com/
> 
> If someone feels strongly about this, I can certainly remove the
> "linux," part from the string - it probably wouldn't the only place where
> one can't reuse a DT snippet as-is between linux and U-Boot.
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> ---
>   .../watchdog/gpio-wdt.txt                     | 15 ++++++
>   drivers/watchdog/Kconfig                      |  7 +++
>   drivers/watchdog/Makefile                     |  1 +
>   drivers/watchdog/gpio_wdt.c                   | 51 +++++++++++++++++++
>   4 files changed, 74 insertions(+)
>   create mode 100644 doc/device-tree-bindings/watchdog/gpio-wdt.txt
>   create mode 100644 drivers/watchdog/gpio_wdt.c
> 
> diff --git a/doc/device-tree-bindings/watchdog/gpio-wdt.txt b/doc/device-tree-bindings/watchdog/gpio-wdt.txt
> new file mode 100644
> index 0000000000..2283b7ba6e
> --- /dev/null
> +++ b/doc/device-tree-bindings/watchdog/gpio-wdt.txt
> @@ -0,0 +1,15 @@
> +GPIO watchdog timer
> +
> +Describes a simple watchdog timer which is reset by toggling a gpio.
> +
> +Required properties:
> +
> +- compatible: must be "linux,wdt-gpio"
> +- gpios: gpio to toggle when wdt driver reset method is called
> +
> +Example:
> +
> +	gpio-wdt {
> +		gpios = <&gpio0 1 0>;
> +		compatible = "linux,wdt-gpio";
> +	};
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index f0ff2612a6..2cf378db29 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -147,6 +147,13 @@ config WDT_CORTINA
>   	  This driver support all CPU ISAs supported by Cortina
>   	  Access CAxxxx SoCs.
>   
> +config WDT_GPIO
> +	bool "External gpio watchdog support"
> +	depends on WDT
> +	depends on DM_GPIO
> +	help
> +	   Support for external watchdog fed by toggling a gpio.
> +
>   config WDT_MPC8xx
>   	bool "MPC8xx watchdog timer support"
>   	depends on WDT && MPC8xx
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index 5c7ef593fe..f14415bb8e 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -25,6 +25,7 @@ obj-$(CONFIG_WDT_BOOKE) += booke_wdt.o
>   obj-$(CONFIG_WDT_CORTINA) += cortina_wdt.o
>   obj-$(CONFIG_WDT_ORION) += orion_wdt.o
>   obj-$(CONFIG_WDT_CDNS) += cdns_wdt.o
> +obj-$(CONFIG_WDT_GPIO) += gpio_wdt.o
>   obj-$(CONFIG_WDT_MPC8xx) += mpc8xx_wdt.o
>   obj-$(CONFIG_WDT_MT7620) += mt7620_wdt.o
>   obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o
> diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
> new file mode 100644
> index 0000000000..9dba9c254e
> --- /dev/null
> +++ b/drivers/watchdog/gpio_wdt.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <common.h>
> +#include <dm.h>
> +#include <dm/device_compat.h>
> +#include <wdt.h>
> +#include <asm/gpio.h>
> +
> +struct gpio_wdt_priv {
> +	struct gpio_desc gpio;
> +	int state;
> +};
> +
> +static int gpio_wdt_reset(struct udevice *dev)
> +{
> +	struct gpio_wdt_priv *priv = dev_get_priv(dev);
> +
> +	priv->state = !priv->state;
> +	return dm_gpio_set_value(&priv->gpio, priv->state);
> +}
> +
> +static int dm_probe(struct udevice *dev)
> +{
> +	struct gpio_wdt_priv *priv = dev_get_priv(dev);
> +	int ret;
> +
> +	ret = gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
> +	if (ret < 0) {
> +		dev_err(dev, "Request for wdt gpio failed: %d\n", ret);
> +		return ret;
> +	}
> +	return gpio_wdt_reset(dev);
> +}
> +
> +static const struct wdt_ops gpio_wdt_ops = {
> +	.reset = gpio_wdt_reset,
> +};

I'm noticing that you don't have a "start" function. How is this GPIO
watchdog enabled? Is it "always on"? Or does it start with the first
triggering?

Perhaps it makes sense to add a note about this into the driver to make
this clear.

Thanks,
Stefan

> +
> +static const struct udevice_id gpio_wdt_ids[] = {
> +	{ .compatible = "linux,wdt-gpio" },
> +	{}
> +};
> +
> +U_BOOT_DRIVER(wdt_gpio) = {
> +	.name = "wdt_gpio",
> +	.id = UCLASS_WDT,
> +	.of_match = gpio_wdt_ids,
> +	.ops = &gpio_wdt_ops,
> +	.probe	= dm_probe,
> +	.priv_auto = sizeof(struct gpio_wdt_priv),
> +};
> 


Viele Grüße,
Stefan

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