watchdog: renesas_wwdt: add driver

This driver adds support for the Renesas Window Watchdog Timer (WWDT).
Because it can only be setup once after boot and we cannot know if this
already happened in early boot stages, it is mandated that the firmware
configures the watchdog. Linux then adapts according to the given
setup. Note that this watchdog only reports an overflow to the Error
Control Module (ECM) and does not reset the SoC on its own.

Signed-off-by: Wolfram Sang <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/Kconfig

···
 	  This driver adds watchdog support for the integrated watchdogs in the
 	  Renesas R-Car and other SH-Mobile SoCs (usually named RWDT or SWDT).
 
+config RENESAS_WWDT
+	tristate "Renesas Window WWDT Watchdog"
+	depends on ARCH_RENESAS || COMPILE_TEST
+	select WATCHDOG_CORE
+	help
+	  This driver adds watchdog support for a window timer found in some
+	  Renesas R-Car Gen3 and later SoCs.
+
 config RENESAS_RZAWDT
 	tristate "Renesas RZ/A WDT Watchdog"
 	depends on ARCH_RENESAS || COMPILE_TEST

drivers/watchdog/Makefile

···
 obj-$(CONFIG_LPC18XX_WATCHDOG) += lpc18xx_wdt.o
 obj-$(CONFIG_BCM7038_WDT) += bcm7038_wdt.o
 obj-$(CONFIG_RENESAS_WDT) += renesas_wdt.o
+obj-$(CONFIG_RENESAS_WWDT) += renesas_wwdt.o
 obj-$(CONFIG_RENESAS_RZAWDT) += rza_wdt.o
 obj-$(CONFIG_RENESAS_RZN1WDT) += rzn1_wdt.o
 obj-$(CONFIG_RENESAS_RZG2LWDT) += rzg2l_wdt.o

drivers/watchdog/renesas_wwdt.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for the Renesas Window Watchdog Timer (WWDT)
+ *
+ * The WWDT can only be setup once after boot. Because we cannot know if this
+ * already happened in early boot stages, it is mandated that the firmware
+ * configures the watchdog. Linux then adapts according to the given setup.
+ * Note that this watchdog reports in the default configuration an overflow to
+ * the Error Control Module which then decides further actions. Or the WWDT is
+ * configured to generate an interrupt.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/watchdog.h>
+
+#define WDTA0WDTE	0x00
+#define WDTA0RUN	BIT(7)
+#define WDTA0_KEY	0x2c
+
+#define WDTA0MD		0x0c
+#define WDTA0OVF(x)	FIELD_GET(GENMASK(6, 4), x)
+#define WDTA0WIE	BIT(3)
+#define WDTA0ERM	BIT(2)
+#define WDTA0WS(x)	FIELD_GET(GENMASK(1, 0), x)
+
+struct wwdt_priv {
+	void __iomem *base;
+	struct watchdog_device wdev;
+};
+
+static int wwdt_start(struct watchdog_device *wdev)
+{
+	struct wwdt_priv *priv = container_of(wdev, struct wwdt_priv, wdev);
+
+	writeb(WDTA0RUN | WDTA0_KEY, priv->base + WDTA0WDTE);
+	return 0;
+}
+
+static const struct watchdog_info wwdt_ident = {
+	.options = WDIOF_KEEPALIVEPING | WDIOF_ALARMONLY,
+	.identity = "Renesas Window Watchdog",
+};
+
+static const struct watchdog_ops wwdt_ops = {
+	.owner = THIS_MODULE,
+	.start = wwdt_start,
+};
+
+static irqreturn_t wwdt_error_irq(int irq, void *dev_id)
+{
+	struct device *dev = dev_id;
+
+	dev_warn(dev, "Watchdog timed out\n");
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t wwdt_pretimeout_irq(int irq, void *dev_id)
+{
+	struct watchdog_device *wdev = dev_id;
+
+	watchdog_notify_pretimeout(wdev);
+	return IRQ_HANDLED;
+}
+
+static int wwdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct wwdt_priv *priv;
+	struct watchdog_device *wdev;
+	struct clk *clk;
+	unsigned long rate;
+	unsigned int interval, window_size;
+	int ret;
+	u8 val;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	clk = devm_clk_get(dev, "cnt");
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	rate = clk_get_rate(clk);
+	if (!rate)
+		return -EINVAL;
+
+	wdev = &priv->wdev;
+
+	val = readb(priv->base + WDTA0WDTE);
+	if (val & WDTA0RUN)
+		set_bit(WDOG_HW_RUNNING, &wdev->status);
+
+	val = readb(priv->base + WDTA0MD);
+	interval = 1 << (9 + WDTA0OVF(val));
+	/* size of the closed(!) window per mille */
+	window_size = 250 * (3 - WDTA0WS(val));
+
+	wdev->info = &wwdt_ident;
+	wdev->ops = &wwdt_ops;
+	wdev->parent = dev;
+	wdev->min_hw_heartbeat_ms = window_size * interval / rate;
+	wdev->max_hw_heartbeat_ms = 1000 * interval / rate;
+	wdev->timeout = DIV_ROUND_UP(wdev->max_hw_heartbeat_ms, 1000);
+	watchdog_set_nowayout(wdev, true);
+
+	if (!(val & WDTA0ERM)) {
+		ret = platform_get_irq_byname(pdev, "error");
+		if (ret < 0)
+			return ret;
+
+		ret = devm_request_threaded_irq(dev, ret, NULL, wwdt_error_irq,
+						IRQF_ONESHOT, NULL, dev);
+		if (ret < 0)
+			return ret;
+	}
+
+	if (val & WDTA0WIE) {
+		ret = platform_get_irq_byname(pdev, "pretimeout");
+		if (ret < 0)
+			return ret;
+
+		ret = devm_request_threaded_irq(dev, ret, NULL, wwdt_pretimeout_irq,
+						IRQF_ONESHOT, NULL, wdev);
+		if (ret < 0)
+			return ret;
+	}
+
+	devm_watchdog_register_device(dev, wdev);
+
+	return 0;
+}
+
+static const struct of_device_id renesas_wwdt_ids[] = {
+	{ .compatible = "renesas,rcar-gen3-wwdt", },
+	{ .compatible = "renesas,rcar-gen4-wwdt", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, renesas_wwdt_ids);
+
+static struct platform_driver renesas_wwdt_driver = {
+	.driver = {
+		.name = "renesas_wwdt",
+		.of_match_table = renesas_wwdt_ids,
+	},
+	.probe = wwdt_probe,
+};
+module_platform_driver(renesas_wwdt_driver);
+
+MODULE_DESCRIPTION("Renesas Window Watchdog (WWDT) Driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Wolfram Sang <[e-mail]>");