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 corresponding linux driver apparently has support for some watchdog circuits which can be disabled by tri-stating the gpio, but I have never actually encountered such a chip in the wild; the whole point of adding an external watchdog is usually that it is not in any way under software control. For forward-compatibility, and to make DT describe the hardware, the current driver only supports devices that have the always-running property. I went a little back and forth on whether I should fail ->probe or only ->start, and ended up deciding ->start was the right place.
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...
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.
Reviewed-by: Simon Glass sjg@chromium.org Reviewed-by: Stefan Roese sr@denx.de Signed-off-by: Rasmus Villemoes rasmus.villemoes@prevas.dk --- .../watchdog/gpio-wdt.txt | 19 ++++++ drivers/watchdog/Kconfig | 9 +++ drivers/watchdog/Makefile | 1 + drivers/watchdog/gpio_wdt.c | 68 +++++++++++++++++++ 4 files changed, 97 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..c9a8559a3e --- /dev/null +++ b/doc/device-tree-bindings/watchdog/gpio-wdt.txt @@ -0,0 +1,19 @@ +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. +- always-running: Boolean property indicating that the watchdog cannot + be disabled. At present, U-Boot only supports this kind of GPIO + watchdog. + +Example: + + gpio-wdt { + gpios = <&gpio0 1 0>; + compatible = "linux,wdt-gpio"; + always-running; + }; diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig index f0ff2612a6..6fbb5c1b6d 100644 --- a/drivers/watchdog/Kconfig +++ b/drivers/watchdog/Kconfig @@ -147,6 +147,15 @@ 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. See + doc/device-tree-bindings/watchdog/gpio-wdt.txt for + information on how to describe the watchdog in device tree. + 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..982a66b3f9 --- /dev/null +++ b/drivers/watchdog/gpio_wdt.c @@ -0,0 +1,68 @@ +// SPDX-License-Identifier: GPL-2.0+ + +#include <dm.h> +#include <dm/device_compat.h> +#include <wdt.h> +#include <asm/gpio.h> + +struct gpio_wdt_priv { + struct gpio_desc gpio; + bool always_running; + 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 gpio_wdt_start(struct udevice *dev, u64 timeout, ulong flags) +{ + struct gpio_wdt_priv *priv = dev_get_priv(dev); + + if (priv->always_running) + return 0; + + return -ENOSYS; +} + +static int dm_probe(struct udevice *dev) +{ + struct gpio_wdt_priv *priv = dev_get_priv(dev); + int ret; + + priv->always_running = dev_read_bool(dev, "always-running"); + 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; + } + + if (priv->always_running) + ret = gpio_wdt_reset(dev); + + return ret; +} + +static const struct wdt_ops gpio_wdt_ops = { + .start = gpio_wdt_start, + .reset = gpio_wdt_reset, +}; + +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), +};