[PATCH v2 1/3] watchdog: Add a driver for the Apple watchdog

[Mark Kettenis]

This driver supports the watchdog timer found on Apple's M1 SoC.
On systems that use these SoC, the watchdog timer is the primary
way to reboot the system.

Signed-off-by: Mark Kettenis <kettenis at openbsd.org>
Reviewed-by: Sven Peter <sven at svenpeter.dev>
Reviewed-by: Simon Glass <sjg at chromium.org>
Reviewed-by: Stefan Roese <sr at denx.de>
Tested-on: Apple M1 Macbook
Tested-by: Simon Glass <sjg at chromium.org>
---

ChangeLog:

v2: - Adjust delay and add comment


 MAINTAINERS                  |   1 +
 drivers/watchdog/Kconfig     |   9 +++
 drivers/watchdog/Makefile    |   1 +
 drivers/watchdog/apple_wdt.c | 115 +++++++++++++++++++++++++++++++++++
 4 files changed, 126 insertions(+)
 create mode 100644 drivers/watchdog/apple_wdt.c

diff --git a/MAINTAINERS b/MAINTAINERS
index f4bd3d79e2..6ae81c5659 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -116,6 +116,7 @@ F:	arch/arm/mach-apple/
 F:	configs/apple_m1_defconfig
 F:	drivers/iommu/apple_dart.c
 F:	drivers/pinctrl/pinctrl-apple.c
+F:	drivers/watchdog/apple_wdt.c
 F:	include/configs/apple.h
 
 ARM
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 1177f17fd8..cabac29053 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -81,6 +81,15 @@ config WDT
 	  What exactly happens when the timer expires is up to a particular
 	  device/driver.
 
+config WDT_APPLE
+	bool "Apple watchdog timer support"
+	depends on WDT
+	default y if ARCH_APPLE
+	help
+	  Enable support for the watchdog timer on Apple SoCs.
+	  The watchdog will perform a full SoC reset resulting in a
+	  reboot of the entire system.
+
 config WDT_ARMADA_37XX
 	bool "Marvell Armada 37xx watchdog timer support"
 	depends on WDT && ARMADA_3700
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index fa7ce583ce..6d2b3822c0 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_DESIGNWARE_WATCHDOG) += designware_wdt.o
 obj-$(CONFIG_ULP_WATCHDOG) += ulp_wdog.o
 obj-$(CONFIG_$(SPL_TPL_)WDT) += wdt-uclass.o
 obj-$(CONFIG_WDT_SANDBOX) += sandbox_wdt.o
+obj-$(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
diff --git a/drivers/watchdog/apple_wdt.c b/drivers/watchdog/apple_wdt.c
new file mode 100644
index 0000000000..c7307f41cb
--- /dev/null
+++ b/drivers/watchdog/apple_wdt.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2021 Mark Kettenis <kettenis at openbsd.org>
+ */
+
+#include <clk.h>
+#include <dm.h>
+#include <wdt.h>
+#include <asm/io.h>
+#include <linux/delay.h>
+
+#define APPLE_WDT_CUR_TIME		0x10
+#define APPLE_WDT_BARK_TIME		0x14
+#define APPLE_WDT_CTRL			0x1c
+#define  APPLE_WDT_CTRL_RESET_EN	BIT(2)
+
+struct apple_wdt_priv {
+	void *base;
+	ulong clk_rate;
+};
+
+static int apple_wdt_reset(struct udevice *dev)
+{
+	struct apple_wdt_priv *priv = dev_get_priv(dev);
+
+	writel(0, priv->base + APPLE_WDT_CUR_TIME);
+
+	return 0;
+}
+
+static int apple_wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
+{
+	struct apple_wdt_priv *priv = dev_get_priv(dev);
+	u64 timeout;
+
+	timeout = (timeout_ms * priv->clk_rate) / 1000;
+	if (timeout > U32_MAX)
+		return -EINVAL;
+
+	writel(0, priv->base + APPLE_WDT_CUR_TIME);
+	writel(timeout, priv->base + APPLE_WDT_BARK_TIME);
+	writel(APPLE_WDT_CTRL_RESET_EN, priv->base + APPLE_WDT_CTRL);
+
+	return 0;
+}
+
+static int apple_wdt_stop(struct udevice *dev)
+{
+	struct apple_wdt_priv *priv = dev_get_priv(dev);
+
+	writel(0, priv->base + APPLE_WDT_CTRL);
+
+	return 0;
+}
+
+static int apple_wdt_expire_now(struct udevice *dev, ulong flags)
+{
+	int ret;
+
+	ret = apple_wdt_start(dev, 0, flags);
+	if (ret)
+		return ret;
+
+	/*
+	 * It can take up to 25ms until the SoC actually resets, so
+	 * wait 50ms just to be sure.
+	 */
+	mdelay(50);
+
+	return 0;
+}
+
+static const struct wdt_ops apple_wdt_ops = {
+	.reset = apple_wdt_reset,
+	.start = apple_wdt_start,
+	.stop = apple_wdt_stop,
+	.expire_now = apple_wdt_expire_now,
+};
+
+static const struct udevice_id apple_wdt_ids[] = {
+	{ .compatible = "apple,wdt" },
+	{ /* sentinel */ }
+};
+
+static int apple_wdt_probe(struct udevice *dev)
+{
+	struct apple_wdt_priv *priv = dev_get_priv(dev);
+	struct clk clk;
+	int ret;
+
+	priv->base = dev_read_addr_ptr(dev);
+	if (!priv->base)
+		return -EINVAL;
+
+	ret = clk_get_by_index(dev, 0, &clk);
+	if (ret)
+		return ret;
+
+	ret = clk_enable(&clk);
+	if (ret)
+		return ret;
+
+	priv->clk_rate = clk_get_rate(&clk);
+
+	return 0;
+}
+
+U_BOOT_DRIVER(apple_wdt) = {
+	.name = "apple_wdt",
+	.id = UCLASS_WDT,
+	.of_match = apple_wdt_ids,
+	.priv_auto = sizeof(struct apple_wdt_priv),
+	.probe = apple_wdt_probe,
+	.ops = &apple_wdt_ops,
+};
-- 
2.34.1