watchdog: Add a watchdog driver for Raspberry Pi boards

This driver supports the bcm2835 watchdog found on
Raspberry Pi boards.
It is derived from the Linux driver and was tested
on two Raspberry Pi board versions (B+ and 3B+).

Signed-off-by: Etienne Dublé <etienne.duble@imag.fr>
Reviewed-by: Stefan Roese <sr@denx.de>

drivers/watchdog/Kconfig

@@ -31,6 +31,7 @@ config WATCHDOG_TIMEOUT_MSECS
 	default 30000 if ARCH_SOCFPGA
 	default 16000 if ARCH_SUNXI
 	default 5376 if ULP_WATCHDOG
+	default 15000 if ARCH_BCM283X
 	default 60000
 	help
 	  Watchdog timeout in msec
@@ -327,6 +328,14 @@ config WDT_SUNXI
 	help
 	  Enable support for the watchdog timer in Allwinner sunxi SoCs.
 
+config WDT_BCM2835
+	bool "Broadcom 2835 watchdog timer support"
+	depends on WDT && ARCH_BCM283X
+	default y
+	help
+	  Enable support for the watchdog timer in Broadcom 283X SoCs such
+	  as Raspberry Pi boards.
+
 config XILINX_TB_WATCHDOG
 	bool "Xilinx Axi watchdog timer support"
 	depends on WDT

drivers/watchdog/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_WDT_APPLE) += apple_wdt.o
 obj-$(CONFIG_WDT_ARMADA_37XX) += armada-37xx-wdt.o
 obj-$(CONFIG_WDT_ASPEED) += ast_wdt.o
 obj-$(CONFIG_WDT_AST2600) += ast2600_wdt.o
+obj-$(CONFIG_WDT_BCM2835) += bcm2835_wdt.o
 obj-$(CONFIG_WDT_BCM6345) += bcm6345_wdt.o
 obj-$(CONFIG_WDT_BOOKE) += booke_wdt.o
 obj-$(CONFIG_WDT_CORTINA) += cortina_wdt.o

drivers/watchdog/bcm2835_wdt.c

@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2013 Lubomir Rintel <lkundrak@v3.sk>
+ * Copyright (C) 2023 Etienne Dublé (CNRS) <etienne.duble@imag.fr>
+ *
+ * This code is mostly derived from the linux driver.
+ */
+
+#include <dm.h>
+#include <wdt.h>
+#include <asm/io.h>
+#include <linux/delay.h>
+
+#define PM_RSTC					0x1c
+#define PM_WDOG					0x24
+
+#define PM_PASSWORD				0x5a000000
+
+/* The hardware supports a maximum timeout value of 0xfffff ticks
+ * (just below 16 seconds).
+ */
+#define PM_WDOG_MAX_TICKS			0x000fffff
+#define PM_RSTC_WRCFG_CLR			0xffffffcf
+#define PM_RSTC_WRCFG_FULL_RESET		0x00000020
+#define PM_RSTC_RESET				0x00000102
+
+#define MS_TO_WDOG_TICKS(x) (((x) << 16) / 1000)
+
+struct bcm2835_wdt_priv {
+	void __iomem *base;
+	u64 timeout_ticks;
+};
+
+static int bcm2835_wdt_start_ticks(struct udevice *dev,
+				   u64 timeout_ticks, ulong flags)
+{
+	struct bcm2835_wdt_priv *priv = dev_get_priv(dev);
+	void __iomem *base = priv->base;
+	u32 cur;
+
+	writel(PM_PASSWORD | timeout_ticks, base + PM_WDOG);
+	cur = readl(base + PM_RSTC);
+	writel(PM_PASSWORD | (cur & PM_RSTC_WRCFG_CLR) | PM_RSTC_WRCFG_FULL_RESET,
+	       base + PM_RSTC);
+
+	return 0;
+}
+
+static int bcm2835_wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
+{
+	struct bcm2835_wdt_priv *priv = dev_get_priv(dev);
+
+	priv->timeout_ticks = MS_TO_WDOG_TICKS(timeout_ms);
+
+	if (priv->timeout_ticks > PM_WDOG_MAX_TICKS) {
+		printf("bcm2835_wdt: the timeout value is too high, using ~16s instead.\n");
+		priv->timeout_ticks = PM_WDOG_MAX_TICKS;
+	}
+
+	return bcm2835_wdt_start_ticks(dev, priv->timeout_ticks, flags);
+}
+
+static int bcm2835_wdt_reset(struct udevice *dev)
+{
+	struct bcm2835_wdt_priv *priv = dev_get_priv(dev);
+
+	/* restart the timer with the value of priv->timeout_ticks
+	 * saved from the last bcm2835_wdt_start() call.
+	 */
+	return bcm2835_wdt_start_ticks(dev, priv->timeout_ticks, 0);
+}
+
+static int bcm2835_wdt_stop(struct udevice *dev)
+{
+	struct bcm2835_wdt_priv *priv = dev_get_priv(dev);
+	void __iomem *base = priv->base;
+
+	writel(PM_PASSWORD | PM_RSTC_RESET, base + PM_RSTC);
+
+	return 0;
+}
+
+static int bcm2835_wdt_expire_now(struct udevice *dev, ulong flags)
+{
+	int ret;
+
+	/* use a timeout of 10 ticks (~150us) */
+	ret = bcm2835_wdt_start_ticks(dev, 10, flags);
+	if (ret)
+		return ret;
+
+	mdelay(500);
+
+	return 0;
+}
+
+static const struct wdt_ops bcm2835_wdt_ops = {
+	.reset		= bcm2835_wdt_reset,
+	.start		= bcm2835_wdt_start,
+	.stop		= bcm2835_wdt_stop,
+	.expire_now	= bcm2835_wdt_expire_now,
+};
+
+static const struct udevice_id bcm2835_wdt_ids[] = {
+	{ .compatible = "brcm,bcm2835-pm" },
+	{ .compatible = "brcm,bcm2835-pm-wdt" },
+	{ /* sentinel */ }
+};
+
+static int bcm2835_wdt_probe(struct udevice *dev)
+{
+	struct bcm2835_wdt_priv *priv = dev_get_priv(dev);
+
+	priv->base = dev_remap_addr(dev);
+	if (!priv->base)
+		return -EINVAL;
+
+	priv->timeout_ticks = PM_WDOG_MAX_TICKS;
+
+	bcm2835_wdt_stop(dev);
+
+	return 0;
+}
+
+U_BOOT_DRIVER(bcm2835_wdt) = {
+	.name		= "bcm2835_wdt",
+	.id		= UCLASS_WDT,
+	.of_match	= bcm2835_wdt_ids,
+	.probe		= bcm2835_wdt_probe,
+	.priv_auto	= sizeof(struct bcm2835_wdt_priv),
+	.ops		= &bcm2835_wdt_ops,
+};