watchdog: add pulse support to gpio watchdog driver

A common external watchdog circuit is kept alive by triggering a short
pulse on the reset pin. This patch adds support for this use case, while
making the algorithm configurable in the devicetree.

The "linux,wdt-gpio" driver being modified is based off the equivalent
driver in the Linux kernel, which provides support for this algorithm.
This patch brings parity to this driver, and is kept aligned with
the functionality and devicetree configuration in the kernel.

It should be noted that this adds a required property named 'hw_algo'
to the devicetree binding, following suit with the kernel. I'm happy to
make this backward-compatible if preferred.

Signed-off-by: Paul Doelle <paaull.git@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/sandbox/dts/test.dts

@@ -850,10 +850,19 @@
 		};
 	};
 
-	gpio-wdt {
+	wdt-gpio-toggle {
 		gpios = <&gpio_a 7 0>;
 		compatible = "linux,wdt-gpio";
 		hw_margin_ms = <100>;
+		hw_algo = "toggle";
+		always-running;
+	};
+
+	wdt-gpio-level {
+		gpios = <&gpio_a 7 0>;
+		compatible = "linux,wdt-gpio";
+		hw_margin_ms = <100>;
+		hw_algo = "level";
 		always-running;
 	};
 

doc/device-tree-bindings/watchdog/gpio-wdt.txt

@@ -5,7 +5,12 @@ 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.
+- gpios: From common gpio binding; gpio connection to WDT reset pin.
+- hw_algo: The algorithm used by the driver. Should be one of the
+  following values:
+  - toggle: Toggle from high-to-low or low-to-high when resetting the watchdog.
+  - level: Maintain a constant high/low level, and trigger a short pulse when
+    resetting the watchdog. Active level is determined by the GPIO flags.
 - always-running: Boolean property indicating that the watchdog cannot
   be disabled. At present, U-Boot only supports this kind of GPIO
   watchdog.
@@ -15,5 +20,6 @@ Example:
 	gpio-wdt {
 		gpios = <&gpio0 1 0>;
 		compatible = "linux,wdt-gpio";
+		hw_algo = "toggle";
 		always-running;
 	};

drivers/watchdog/gpio_wdt.c

@@ -4,20 +4,38 @@
 #include <dm/device_compat.h>
 #include <wdt.h>
 #include <asm/gpio.h>
+#include <linux/delay.h>
+
+enum {
+	HW_ALGO_TOGGLE,
+	HW_ALGO_LEVEL,
+};
 
 struct gpio_wdt_priv {
-	struct gpio_desc gpio;
-	bool always_running;
-	int state;
+	struct		gpio_desc gpio;
+	unsigned int	hw_algo;
+	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);
+	switch (priv->hw_algo) {
+	case HW_ALGO_TOGGLE:
+		/* Toggle output pin */
+		priv->state = !priv->state;
+		dm_gpio_set_value(&priv->gpio, priv->state);
+		break;
+	case HW_ALGO_LEVEL:
+		/* Pulse */
+		dm_gpio_set_value(&priv->gpio, 1);
+		udelay(1);
+		dm_gpio_set_value(&priv->gpio, 0);
+		break;
+	}
+	return 0;
 }
 
 static int gpio_wdt_start(struct udevice *dev, u64 timeout, ulong flags)
@@ -34,6 +52,16 @@ static int dm_probe(struct udevice *dev)
 {
 	struct gpio_wdt_priv *priv = dev_get_priv(dev);
 	int ret;
+	const char *algo = dev_read_string(dev, "hw_algo");
+
+	if (!algo)
+		return -EINVAL;
+	if (!strcmp(algo, "toggle"))
+		priv->hw_algo = HW_ALGO_TOGGLE;
+	else if (!strcmp(algo, "level"))
+		priv->hw_algo = HW_ALGO_LEVEL;
+	else
+		return -EINVAL;
 
 	priv->always_running = dev_read_bool(dev, "always-running");
 	ret = gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);

test/dm/wdt.c

@@ -44,20 +44,20 @@ static int dm_test_wdt_base(struct unit_test_state *uts)
 }
 DM_TEST(dm_test_wdt_base, UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);
 
-static int dm_test_wdt_gpio(struct unit_test_state *uts)
+static int dm_test_wdt_gpio_toggle(struct unit_test_state *uts)
 {
 	/*
 	 * The sandbox wdt gpio is "connected" to gpio bank a, offset
 	 * 7. Use the sandbox back door to verify that the gpio-wdt
-	 * driver behaves as expected.
+	 * driver behaves as expected when using the 'toggle' algorithm.
 	 */
 	struct udevice *wdt, *gpio;
 	const u64 timeout = 42;
 	const int offset = 7;
 	int val;
 
-	ut_assertok(uclass_get_device_by_driver(UCLASS_WDT,
-						DM_DRIVER_GET(wdt_gpio), &wdt));
+	ut_assertok(uclass_get_device_by_name(UCLASS_WDT,
+					      "wdt-gpio-toggle", &wdt));
 	ut_assertnonnull(wdt);
 
 	ut_assertok(uclass_get_device_by_name(UCLASS_GPIO, "base-gpios", &gpio));
@@ -74,7 +74,39 @@ static int dm_test_wdt_gpio(struct unit_test_state *uts)
 
 	return 0;
 }
-DM_TEST(dm_test_wdt_gpio, UT_TESTF_SCAN_FDT);
+DM_TEST(dm_test_wdt_gpio_toggle, UT_TESTF_SCAN_FDT);
+
+static int dm_test_wdt_gpio_level(struct unit_test_state *uts)
+{
+	/*
+	 * The sandbox wdt gpio is "connected" to gpio bank a, offset
+	 * 7. Use the sandbox back door to verify that the gpio-wdt
+	 * driver behaves as expected when using the 'level' algorithm.
+	 */
+	struct udevice *wdt, *gpio;
+	const u64 timeout = 42;
+	const int offset = 7;
+	int val;
+
+	ut_assertok(uclass_get_device_by_name(UCLASS_WDT,
+					      "wdt-gpio-level", &wdt));
+	ut_assertnonnull(wdt);
+
+	ut_assertok(uclass_get_device_by_name(UCLASS_GPIO, "base-gpios", &gpio));
+	ut_assertnonnull(gpio);
+	ut_assertok(wdt_start(wdt, timeout, 0));
+
+	val = sandbox_gpio_get_value(gpio, offset);
+	ut_assertok(wdt_reset(wdt));
+	ut_asserteq(val, sandbox_gpio_get_value(gpio, offset));
+	ut_assertok(wdt_reset(wdt));
+	ut_asserteq(val, sandbox_gpio_get_value(gpio, offset));
+
+	ut_asserteq(-ENOSYS, wdt_stop(wdt));
+
+	return 0;
+}
+DM_TEST(dm_test_wdt_gpio_level, UT_TESTF_SCAN_FDT);
 
 static int dm_test_wdt_watchdog_reset(struct unit_test_state *uts)
 {
@@ -86,8 +118,8 @@ static int dm_test_wdt_watchdog_reset(struct unit_test_state *uts)
 	uint reset_count;
 	int val;
 
-	ut_assertok(uclass_get_device_by_driver(UCLASS_WDT,
-						DM_DRIVER_GET(wdt_gpio), &gpio_wdt));
+	ut_assertok(uclass_get_device_by_name(UCLASS_WDT,
+					      "wdt-gpio-toggle", &gpio_wdt));
 	ut_assertnonnull(gpio_wdt);
 	ut_assertok(uclass_get_device_by_driver(UCLASS_WDT,
 						DM_DRIVER_GET(wdt_sandbox), &sandbox_wdt));