[PATCH v2 2/2] watchdog: Add Apple SoC watchdog driver

[Sven Peter <sven@svenpeter.dev>]

Add support for the watchdog timer found in Apple SoCs. This driver is
also required to reboot these machines.

Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
v1 -> v2:
 - set the default timeout to 30s and call watchdog_init_timeout
   to allow the device tree to override it
 - set WDOG_HW_RUNNING if the watchdog is enabled at boot
 - check that the clock rate is not zero
 - use unsigned long instead of u32 for clk_rate
 - use devm_add_action_or_reset instead of manually calling
   clk_disable_unprepare
 - explain the magic number in apple_wdt_restart

 MAINTAINERS                  |   1 +
 drivers/watchdog/Kconfig     |  12 ++
 drivers/watchdog/Makefile    |   1 +
 drivers/watchdog/apple_wdt.c | 226 +++++++++++++++++++++++++++++++++++
 4 files changed, 240 insertions(+)
 create mode 100644 drivers/watchdog/apple_wdt.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 859201bbd4e8..6190f0b40983 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1757,6 +1757,7 @@ F:	drivers/i2c/busses/i2c-pasemi-platform.c
 F:	drivers/irqchip/irq-apple-aic.c
 F:	drivers/mailbox/apple-mailbox.c
 F:	drivers/pinctrl/pinctrl-apple-gpio.c
+F:	drivers/watchdog/apple_wdt.c
 F:	include/dt-bindings/interrupt-controller/apple-aic.h
 F:	include/dt-bindings/pinctrl/apple.h
 F:	include/linux/apple-mailbox.h
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 9d222ba17ec6..170dec880c8f 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -976,6 +976,18 @@ config MSC313E_WATCHDOG
 	  To compile this driver as a module, choose M here: the
 	  module will be called msc313e_wdt.
 
+config APPLE_WATCHDOG
+	tristate "Apple SoC watchdog"
+	depends on ARCH_APPLE || COMPILE_TEST
+	select WATCHDOG_CORE
+	help
+	  Say Y here to include support for the Watchdog found in Apple
+	  SoCs such as the M1. Next to the common watchdog features this
+	  driver is also required in order to reboot these SoCs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called apple_wdt.
+
 # X86 (i386 + ia64 + x86_64) Architecture
 
 config ACQUIRE_WDT
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index 2ee97064145b..270a518bd8f3 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -93,6 +93,7 @@ obj-$(CONFIG_PM8916_WATCHDOG) += pm8916_wdt.o
 obj-$(CONFIG_ARM_SMC_WATCHDOG) += arm_smc_wdt.o
 obj-$(CONFIG_VISCONTI_WATCHDOG) += visconti_wdt.o
 obj-$(CONFIG_MSC313E_WATCHDOG) += msc313e_wdt.o
+obj-$(CONFIG_APPLE_WATCHDOG) += apple_wdt.o
 
 # X86 (i386 + ia64 + x86_64) Architecture
 obj-$(CONFIG_ACQUIRE_WDT) += acquirewdt.o
diff --git a/drivers/watchdog/apple_wdt.c b/drivers/watchdog/apple_wdt.c
new file mode 100644
index 000000000000..76e5bedd50d1
--- /dev/null
+++ b/drivers/watchdog/apple_wdt.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple SoC Watchdog driver
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/watchdog.h>
+
+/*
+ * Apple Watchdog MMIO registers
+ *
+ * This HW block has three separate watchdogs. WD0 resets the machine
+ * to recovery mode and is not very useful for us. WD1 and WD2 trigger a normal
+ * machine reset. WD0 additionally supports a configurable interrupt.
+ * This information can be used to implement pretimeout support at a later time.
+ *
+ * APPLE_WDT_WDx_CUR_TIME is a simple counter incremented for each tick of the
+ * reference clock. It can also be overwritten to any value.
+ * Whenever APPLE_WDT_CTRL_RESET_EN is set in APPLE_WDT_WDx_CTRL and
+ * APPLE_WDTx_WD1_CUR_TIME >= APPLE_WDTx_WD1_BITE_TIME the entire machine is
+ * reset.
+ * Whenever APPLE_WDT_CTRL_IRQ_EN is set and APPLE_WDTx_WD1_CUR_TIME >=
+ * APPLE_WDTx_WD1_BARK_TIME an interrupt is triggered and
+ * APPLE_WDT_CTRL_IRQ_STATUS is set. The interrupt can be cleared by writing
+ * 1 to APPLE_WDT_CTRL_IRQ_STATUS.
+ */
+#define APPLE_WDT_WD0_CUR_TIME		0x00
+#define APPLE_WDT_WD0_BITE_TIME		0x04
+#define APPLE_WDT_WD0_BARK_TIME		0x08
+#define APPLE_WDT_WD0_CTRL		0x0c
+
+#define APPLE_WDT_WD1_CUR_TIME		0x10
+#define APPLE_WDT_WD1_BITE_TIME		0x14
+#define APPLE_WDT_WD1_CTRL		0x1c
+
+#define APPLE_WDT_WD2_CUR_TIME		0x20
+#define APPLE_WDT_WD2_BITE_TIME		0x24
+#define APPLE_WDT_WD2_CTRL		0x2c
+
+#define APPLE_WDT_CTRL_IRQ_EN		BIT(0)
+#define APPLE_WDT_CTRL_IRQ_STATUS	BIT(1)
+#define APPLE_WDT_CTRL_RESET_EN		BIT(2)
+
+#define APPLE_WDT_TIMEOUT_DEFAULT	30
+
+struct apple_wdt {
+	struct watchdog_device wdd;
+	void __iomem *regs;
+	unsigned long clk_rate;
+};
+
+static struct apple_wdt *to_apple_wdt(struct watchdog_device *wdd)
+{
+	return container_of(wdd, struct apple_wdt, wdd);
+}
+
+static int apple_wdt_start(struct watchdog_device *wdd)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+	writel_relaxed(APPLE_WDT_CTRL_RESET_EN, wdt->regs + APPLE_WDT_WD1_CTRL);
+
+	return 0;
+}
+
+static int apple_wdt_stop(struct watchdog_device *wdd)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CTRL);
+
+	return 0;
+}
+
+static int apple_wdt_ping(struct watchdog_device *wdd)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+
+	return 0;
+}
+
+static int apple_wdt_set_timeout(struct watchdog_device *wdd, unsigned int s)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+	writel_relaxed(wdt->clk_rate * s, wdt->regs + APPLE_WDT_WD1_BITE_TIME);
+
+	wdd->timeout = s;
+
+	return 0;
+}
+
+static unsigned int apple_wdt_get_timeleft(struct watchdog_device *wdd)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+	u32 cur_time, reset_time;
+
+	cur_time = readl_relaxed(wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+	reset_time = readl_relaxed(wdt->regs + APPLE_WDT_WD1_BITE_TIME);
+
+	return (reset_time - cur_time) / wdt->clk_rate;
+}
+
+static int apple_wdt_restart(struct watchdog_device *wdd, unsigned long mode,
+			     void *cmd)
+{
+	struct apple_wdt *wdt = to_apple_wdt(wdd);
+
+	writel_relaxed(APPLE_WDT_CTRL_RESET_EN, wdt->regs + APPLE_WDT_WD1_CTRL);
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_BITE_TIME);
+	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+
+	/*
+	 * Flush writes and then wait for the SoC to reset. Even though the
+	 * reset is queued almost immediately experiments have shown that it
+	 * can take up to ~20-25ms until the SoC is actually reset. Just wait
+	 * 50ms here to be safe.
+	 */
+	(void)readl_relaxed(wdt->regs + APPLE_WDT_WD1_CUR_TIME);
+	mdelay(50);
+
+	return 0;
+}
+
+static void apple_wdt_clk_disable_unprepare(void *data)
+{
+	clk_disable_unprepare(data);
+}
+
+static struct watchdog_ops apple_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = apple_wdt_start,
+	.stop = apple_wdt_stop,
+	.ping = apple_wdt_ping,
+	.set_timeout = apple_wdt_set_timeout,
+	.get_timeleft = apple_wdt_get_timeleft,
+	.restart = apple_wdt_restart,
+};
+
+static struct watchdog_info apple_wdt_info = {
+	.identity = "Apple SoC Watchdog",
+	.options = WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT,
+};
+
+static int apple_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct apple_wdt *wdt;
+	struct clk *clk;
+	u32 wdt_ctrl;
+	int ret;
+
+	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
+	if (!wdt)
+		return -ENOMEM;
+
+	wdt->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(wdt->regs))
+		return PTR_ERR(wdt->regs);
+
+	clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	ret = clk_prepare_enable(clk);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(dev, apple_wdt_clk_disable_unprepare,
+				       clk);
+	if (ret)
+		return ret;
+
+	wdt->clk_rate = clk_get_rate(clk);
+	if (!wdt->clk_rate)
+		return -EINVAL;
+
+	wdt->wdd.ops = &apple_wdt_ops;
+	wdt->wdd.info = &apple_wdt_info;
+	wdt->wdd.max_timeout = U32_MAX / wdt->clk_rate;
+	wdt->wdd.timeout = APPLE_WDT_TIMEOUT_DEFAULT;
+
+	wdt_ctrl = readl_relaxed(wdt->regs + APPLE_WDT_WD1_CTRL);
+	if (wdt_ctrl & APPLE_WDT_CTRL_RESET_EN)
+		set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
+
+	watchdog_init_timeout(&wdt->wdd, 0, dev);
+	apple_wdt_set_timeout(&wdt->wdd, wdt->wdd.timeout);
+	watchdog_stop_on_unregister(&wdt->wdd);
+	watchdog_set_restart_priority(&wdt->wdd, 128);
+
+	return devm_watchdog_register_device(dev, &wdt->wdd);
+}
+
+static const struct of_device_id apple_wdt_of_match[] = {
+	{ .compatible = "apple,wdt" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, apple_wdt_of_match);
+
+static struct platform_driver apple_wdt_driver = {
+	.driver = {
+		.name = "apple-watchdog",
+		.of_match_table = apple_wdt_of_match,
+	},
+	.probe = apple_wdt_probe,
+};
+module_platform_driver(apple_wdt_driver);
+
+MODULE_DESCRIPTION("Apple SoC watchdog driver");
+MODULE_AUTHOR("Sven Peter <sven@svenpeter.dev>");
+MODULE_LICENSE("Dual MIT/GPL");
-- 
2.25.1