[PATCH v4 08/10] watchdog: add gpio watchdog driver

Rasmus Villemoes
2021-08-02T15:02:34Z

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_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.

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),
+};
--
2.31.1