watchdog: Add Renesas R-Car Gen5 window watchdog driver

Add support of Renesas R-Car Gen5 window watchdog timer. Timeout
configuration is derived from CONFIG_WATCHDOG_TIMEOUT_MSECS, which
is more accurate than the 1-second granularity 'timeout' passed to
.start callback.

Reviewed-by: Stefan Roese <stefan.roese@mailbox.org>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

drivers/watchdog/Kconfig

@@ -356,6 +356,13 @@ config WDT_RENESAS
 	help
 	  Enables Renesas SoC R8A779F0 watchdog timer support.
 
+config WDT_RENESAS_WWDT
+	bool "Renesas window watchdog timer support"
+	depends on WDT
+	select SYSCON
+	help
+	  Enables Renesas window watchdog timer support.
+
 config WDT_SANDBOX
 	bool "Enable Watchdog Timer support for Sandbox"
 	depends on SANDBOX && WDT

drivers/watchdog/Makefile

@@ -44,6 +44,7 @@ obj-$(CONFIG_WDT_NPCM) += npcm_wdt.o
 obj-$(CONFIG_WDT_OCTEONTX) += octeontx_wdt.o
 obj-$(CONFIG_WDT_OMAP3) += omap_wdt.o
 obj-$(CONFIG_WDT_RENESAS) += renesas_wdt.o
+obj-$(CONFIG_WDT_RENESAS_WWDT) += renesas_wwdt.o
 obj-$(CONFIG_WDT_SBSA) += sbsa_gwdt.o
 obj-$(CONFIG_WDT_K3_RTI) += rti_wdt.o
 obj-$(CONFIG_WDT_SIEMENS_PMIC) += siemens_pmic_wdt.o

drivers/watchdog/renesas_wwdt.c

@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2026 Marek Vasut <marek.vasut+renesas@mailbox.org>
+ */
+
+#include <asm/io.h>
+#include <clk.h>
+#include <dm/device_compat.h>
+#include <dm.h>
+#include <linux/bitfield.h>
+#include <linux/iopoll.h>
+#include <regmap.h>
+#include <syscon.h>
+#include <wdt.h>
+
+#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) & (_mask))
+
+#define RSIP_CTL_CFG4		0xc0
+#define RSIP_CTL_CFG4_OPWDEN	BIT(3)
+#define RSIP_CTL_CFG4_OPWDVAC	BIT(5)
+
+#define WDTA0_ACT_CODE		0xac
+#define WDTA0WDTE		0x0
+#define WDTA0EVAC		0x4
+#define WDTA0REF		0x8
+#define WDTA0MD			0xc
+#define WDTA0MD_OVF_MASK	GENMASK(6, 4)
+#define WDTA0MD_OVF(n)		field_prep(WDTA0MD_OVF_MASK, (n))
+#define WDTA0MD_NWIE		BIT(3)
+#define WDTA0MD_NERM		BIT(2)
+#define WDTA0MD_NVS_MASK	GENMASK(1, 0)
+#define WDTA0MD_NVS_75P		FIELD_PREP(WDTA0MD_NVS_MASK, 3)
+
+struct wwdt_priv {
+	void __iomem *base;
+	struct regmap *ctl;
+	unsigned int timeout;
+};
+
+/**
+ * wwdt_reset() - Reset or ping Window WDT
+ * @dev: Watchdog device
+ */
+static int wwdt_reset(struct udevice *dev)
+{
+	struct wwdt_priv *priv = dev_get_priv(dev);
+	const u32 cfg = readl(priv->ctl->ranges[0].start + RSIP_CTL_CFG4);
+	u32 rv;
+
+	/* WDT disabled, do nothing. */
+	if (!(cfg & RSIP_CTL_CFG4_OPWDEN))
+		return 0;
+
+	/* WDT with variable activation code */
+	if (cfg & RSIP_CTL_CFG4_OPWDVAC) {
+		rv = readb(priv->base + WDTA0REF);
+		rv = WDTA0_ACT_CODE - rv;
+		writeb(rv, priv->base + WDTA0EVAC);
+	} else {
+		writeb(WDTA0_ACT_CODE, priv->base + WDTA0WDTE);
+	}
+
+	return 0;
+}
+
+/**
+ * wwdt_start() - Start Window WDT
+ * @dev: Watchdog device
+ * @timeout: Watchdog timeout (not used)
+ * @flags: Flags (not used)
+ */
+static int wwdt_start(struct udevice *dev, u64 timeout, ulong flags)
+{
+	struct wwdt_priv *priv = dev_get_priv(dev);
+
+	clrsetbits_8(priv->base + WDTA0MD,
+		     WDTA0MD_OVF_MASK | WDTA0MD_NWIE |
+		     WDTA0MD_NERM | WDTA0MD_NVS_MASK,
+		     WDTA0MD_OVF(priv->timeout) | WDTA0MD_NWIE |
+		     WDTA0MD_NVS_75P);
+
+	wwdt_reset(dev);
+
+	return 0;
+}
+
+/**
+ * wwdt_probe() - Initialize Window WDT hardware
+ * @dev: Watchdog device
+ */
+static int wwdt_probe(struct udevice *dev)
+{
+	struct wwdt_priv *priv = dev_get_priv(dev);
+	struct udevice *syscon;
+	unsigned long rate;
+	struct clk *clk;
+	int ret;
+
+	priv->base = dev_remap_addr(dev);
+	if (!priv->base)
+		return -EINVAL;
+
+	ret = uclass_get_device_by_phandle(UCLASS_SYSCON, dev, "syscon", &syscon);
+	if (ret) {
+		dev_err(dev, "Failed to get syscon\n");
+		return ret;
+	}
+
+	priv->ctl = syscon_get_regmap(syscon);
+	if (!priv->ctl) {
+		dev_err(dev, "Failed to get regmap\n");
+		return -ENODEV;
+	}
+
+	clk = devm_clk_get(dev, "cnt");
+	if (IS_ERR(clk)) {
+		ret = PTR_ERR(clk);
+		dev_err(dev, "Failed to get counter clock: %d\n", ret);
+		return ret;
+	}
+
+	ret = clk_enable(clk);
+	if (ret)
+		return ret;
+
+	rate = clk_get_rate(clk);
+	if (!rate) {
+		clk_disable(clk);
+		return -ENOENT;
+	}
+
+	/*
+	 * Interval time is in "2^9..2^16 / clk_wdt" range. WDTA0OVFx is
+	 * in 0..7 range. The code below does the WDTA0OVFx calculation
+	 * from "interval_time = (1 << N) / clk_wdt" by caculating the N.
+	 * The N rounded down is MSbit of (interval_time * clk_wdt). The
+	 * result is then clamped to fit into the N in 9..16 range, and
+	 * decremented by 9 to fit into WDTA0OVFx in 0..7 range .
+	 */
+	priv->timeout = clamp(fls(CONFIG_WATCHDOG_TIMEOUT_MSECS * rate) - 1, 9, 16) - 9;
+
+	return 0;
+}
+
+static const struct wdt_ops wwdt_ops = {
+	.start = wwdt_start,
+	.reset = wwdt_reset,
+};
+
+static const struct udevice_id wwdt_ids[] = {
+	{ .compatible = "renesas,rcar-gen5-wwdt" },
+	{}
+};
+
+U_BOOT_DRIVER(wwdt_renesas) = {
+	.name = "wwdt_renesas",
+	.id = UCLASS_WDT,
+	.of_match = wwdt_ids,
+	.ops = &wwdt_ops,
+	.probe	= wwdt_probe,
+	.priv_auto = sizeof(struct wwdt_priv),
+};