[PATCH v4 2/2] watchdog: Add Realtek Otto watchdog timer

[Sander Vanheule]

Realtek MIPS SoCs (platform name Otto) have a watchdog timer with
pretimeout notifitication support. The WDT can (partially) hard reset,
or soft reset the SoC.

This driver implements all features as described in the devicetree
binding, except the phase2 interrupt, and also functions as a restart
handler. The cpu reset mode is considered to be a "warm" restart, since
this mode does not reset all peripherals. Being an embedded system
though, the "cpu" and "software" modes will still cause the bootloader
to run on restart.

It is not known how a forced system reset can be disabled on the
supported platforms. This means that the phase2 interrupt will only fire
at the same time as reset, so implementing phase2 is of little use.

Signed-off-by: Sander Vanheule <sander@xxxxxxxxxxxxx>

---
v3 -> v4:
- Do a full clock probe with clk_prepare_enable
- Cache the clock rate instead of keeping a reference to the clk object
- Only return error value if platform_get_irq_byname fails, that call is
  already verbose enough

v2 -> v3:
- fix off-by-one error in PRESCALE assignment

v1 -> v2:
- drop raw_spinlock, locking is not required
- replace devm_free_irq with disable_irq
- use max_hw_heartbeat_ms instead of max_timeout
- drop redundant timeout value checks
- replace ROUND_CLOSEST by ROUND_UP for tick counts, and flooring
  division for timeout values
- change COMMON_CLK 'select' into 'depends on'
- add MODULE_DEVICE_TABLE for OF ID table
- add realtek,rtl9300 compatible
- drop phase2 irq
---
 MAINTAINERS                         |   7 +
 drivers/watchdog/Kconfig            |  13 +
 drivers/watchdog/Makefile           |   1 +
 drivers/watchdog/realtek_otto_wdt.c | 384 ++++++++++++++++++++++++++++
 4 files changed, 405 insertions(+)
 create mode 100644 drivers/watchdog/realtek_otto_wdt.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 7a2345ce8521..2e255902dd90 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16122,6 +16122,13 @@ S:	Maintained
 F:	include/sound/rt*.h
 F:	sound/soc/codecs/rt*
 
+REALTEK OTTO WATCHDOG
+M:	Sander Vanheule <sander@xxxxxxxxxxxxx>
+L:	linux-watchdog@xxxxxxxxxxxxxxx
+S:	Maintained
+F:	Documentation/devicetree/bindings/watchdog/realtek,otto-wdt.yaml
+F:	driver/watchdog/realtek_otto_wdt.c
+
 REALTEK RTL83xx SMI DSA ROUTER CHIPS
 M:	Linus Walleij <linus.walleij@xxxxxxxxxx>
 S:	Maintained
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 9d222ba17ec6..e64de8cf5dbd 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -940,6 +940,19 @@ config RTD119X_WATCHDOG
 	  Say Y here to include support for the watchdog timer in
 	  Realtek RTD1295 SoCs.
 
+config REALTEK_OTTO_WDT
+	tristate "Realtek Otto MIPS watchdog support"
+	depends on MACH_REALTEK_RTL || COMPILE_TEST
+	depends on COMMON_CLK
+	select WATCHDOG_CORE
+	default MACH_REALTEK_RTL
+	help
+	  Say Y here to include support for the watchdog timer on Realtek
+	  RTL838x, RTL839x, RTL930x SoCs. This watchdog has pretimeout
+	  notifications and system reset on timeout.
+
+	  When built as a module this will be called realtek_otto_wdt.
+
 config SPRD_WATCHDOG
 	tristate "Spreadtrum watchdog support"
 	depends on ARCH_SPRD || COMPILE_TEST
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index 2ee97064145b..cca144bc7cd8 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -170,6 +170,7 @@ obj-$(CONFIG_IMGPDC_WDT) += imgpdc_wdt.o
 obj-$(CONFIG_MT7621_WDT) += mt7621_wdt.o
 obj-$(CONFIG_PIC32_WDT) += pic32-wdt.o
 obj-$(CONFIG_PIC32_DMT) += pic32-dmt.o
+obj-$(CONFIG_REALTEK_OTTO_WDT) += realtek_otto_wdt.o
 
 # PARISC Architecture
 
diff --git a/drivers/watchdog/realtek_otto_wdt.c b/drivers/watchdog/realtek_otto_wdt.c
new file mode 100644
index 000000000000..60058a0c3ec4
--- /dev/null
+++ b/drivers/watchdog/realtek_otto_wdt.c
@@ -0,0 +1,384 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Realtek Otto MIPS platform watchdog
+ *
+ * Watchdog timer that will reset the system after timeout, using the selected
+ * reset mode.
+ *
+ * Counter scaling and timeouts:
+ * - Base prescale of (2 << 25), providing tick duration T_0: 168ms @ 200MHz
+ * - PRESCALE: logarithmic prescaler adding a factor of {1, 2, 4, 8}
+ * - Phase 1: Times out after (PHASE1 + 1) × PRESCALE × T_0
+ *   Generates an interrupt, WDT cannot be stopped after phase 1
+ * - Phase 2: starts after phase 1, times out after (PHASE2 + 1) × PRESCALE × T_0
+ *   Resets the system according to RST_MODE
+ */
+
+#include <linux/bits.h>
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/math.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/reboot.h>
+#include <linux/watchdog.h>
+
+#define OTTO_WDT_REG_CNTR		0x0
+#define OTTO_WDT_CNTR_PING		BIT(31)
+
+#define OTTO_WDT_REG_INTR		0x4
+#define OTTO_WDT_INTR_PHASE_1		BIT(31)
+#define OTTO_WDT_INTR_PHASE_2		BIT(30)
+
+#define OTTO_WDT_REG_CTRL		0x8
+#define OTTO_WDT_CTRL_ENABLE		BIT(31)
+#define OTTO_WDT_CTRL_PRESCALE		GENMASK(30, 29)
+#define OTTO_WDT_CTRL_PHASE1		GENMASK(26, 22)
+#define OTTO_WDT_CTRL_PHASE2		GENMASK(19, 15)
+#define OTTO_WDT_CTRL_RST_MODE		GENMASK(1, 0)
+#define OTTO_WDT_MODE_SOC		0
+#define OTTO_WDT_MODE_CPU		1
+#define OTTO_WDT_MODE_SOFTWARE		2
+#define OTTO_WDT_CTRL_DEFAULT		OTTO_WDT_MODE_CPU
+
+#define OTTO_WDT_PRESCALE_MAX		3
+
+/*
+ * One higher than the max values contained in PHASE{1,2}, since a value of 0
+ * corresponds to one tick.
+ */
+#define OTTO_WDT_PHASE_TICKS_MAX	32
+
+/*
+ * The maximum reset delay is actually 2×32 ticks, but that would require large
+ * pretimeout values for timeouts longer than 32 ticks. Limit the maximum timeout
+ * to 32 + 1 to ensure small pretimeout values can be configured as expected.
+ */
+#define OTTO_WDT_TIMEOUT_TICKS_MAX	(OTTO_WDT_PHASE_TICKS_MAX + 1)
+
+struct otto_wdt_ctrl {
+	struct watchdog_device wdev;
+	struct device *dev;
+	void __iomem *base;
+	unsigned int clk_rate_khz;
+	int irq_phase1;
+};
+
+static int otto_wdt_start(struct watchdog_device *wdev)
+{
+	struct otto_wdt_ctrl *ctrl = watchdog_get_drvdata(wdev);
+	u32 v;
+
+	v = ioread32(ctrl->base + OTTO_WDT_REG_CTRL);
+	v |= OTTO_WDT_CTRL_ENABLE;
+	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	return 0;
+}
+
+static int otto_wdt_stop(struct watchdog_device *wdev)
+{
+	struct otto_wdt_ctrl *ctrl = watchdog_get_drvdata(wdev);
+	u32 v;
+
+	v = ioread32(ctrl->base + OTTO_WDT_REG_CTRL);
+	v &= ~OTTO_WDT_CTRL_ENABLE;
+	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	return 0;
+}
+
+static int otto_wdt_ping(struct watchdog_device *wdev)
+{
+	struct otto_wdt_ctrl *ctrl = watchdog_get_drvdata(wdev);
+
+	iowrite32(OTTO_WDT_CNTR_PING, ctrl->base + OTTO_WDT_REG_CNTR);
+
+	return 0;
+}
+
+static int otto_wdt_tick_ms(struct otto_wdt_ctrl *ctrl, int prescale)
+{
+	return DIV_ROUND_CLOSEST(1 << (25 + prescale), ctrl->clk_rate_khz);
+}
+
+/*
+ * The timer asserts the PHASE1/PHASE2 IRQs when the number of ticks exceeds
+ * the value stored in those fields. This means each phase will run for at least
+ * one tick, so small values need to be clamped to correctly reflect the timeout.
+ */
+static inline unsigned int div_round_ticks(unsigned int val, unsigned int tick_duration,
+		unsigned int min_ticks)
+{
+	return max(min_ticks, DIV_ROUND_UP(val, tick_duration));
+}
+
+static int otto_wdt_determine_timeouts(struct watchdog_device *wdev, unsigned int timeout,
+		unsigned int pretimeout)
+{
+	struct otto_wdt_ctrl *ctrl = watchdog_get_drvdata(wdev);
+	unsigned int pretimeout_ms = pretimeout * 1000;
+	unsigned int timeout_ms = timeout * 1000;
+	unsigned int prescale_next = 0;
+	unsigned int phase1_ticks;
+	unsigned int phase2_ticks;
+	unsigned int total_ticks;
+	unsigned int prescale;
+	unsigned int tick_ms;
+	u32 v;
+
+	do {
+		prescale = prescale_next;
+		if (prescale > OTTO_WDT_PRESCALE_MAX)
+			return -EINVAL;
+
+		tick_ms = otto_wdt_tick_ms(ctrl, prescale);
+		total_ticks = div_round_ticks(timeout_ms, tick_ms, 2);
+		phase1_ticks = div_round_ticks(timeout_ms - pretimeout_ms, tick_ms, 1);
+		phase2_ticks = total_ticks - phase1_ticks;
+
+		prescale_next++;
+	} while (phase1_ticks > OTTO_WDT_PHASE_TICKS_MAX
+		|| phase2_ticks > OTTO_WDT_PHASE_TICKS_MAX);
+
+	v = ioread32(ctrl->base + OTTO_WDT_REG_CTRL);
+
+	v &= ~(OTTO_WDT_CTRL_PRESCALE | OTTO_WDT_CTRL_PHASE1 | OTTO_WDT_CTRL_PHASE2);
+	v |= FIELD_PREP(OTTO_WDT_CTRL_PHASE1, phase1_ticks - 1);
+	v |= FIELD_PREP(OTTO_WDT_CTRL_PHASE2, phase2_ticks - 1);
+	v |= FIELD_PREP(OTTO_WDT_CTRL_PRESCALE, prescale);
+
+	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	timeout_ms = total_ticks * tick_ms;
+	ctrl->wdev.timeout = timeout_ms / 1000;
+
+	pretimeout_ms = phase2_ticks * tick_ms;
+	ctrl->wdev.pretimeout = pretimeout_ms / 1000;
+
+	return 0;
+}
+
+static int otto_wdt_set_timeout(struct watchdog_device *wdev, unsigned int val)
+{
+	return otto_wdt_determine_timeouts(wdev, val, min(wdev->pretimeout, val - 1));
+}
+
+static int otto_wdt_set_pretimeout(struct watchdog_device *wdev, unsigned int val)
+{
+	return otto_wdt_determine_timeouts(wdev, wdev->timeout, val);
+}
+
+static int otto_wdt_restart(struct watchdog_device *wdev, unsigned long reboot_mode,
+		void *data)
+{
+	struct otto_wdt_ctrl *ctrl = watchdog_get_drvdata(wdev);
+	u32 reset_mode;
+	u32 v;
+
+	disable_irq(ctrl->irq_phase1);
+
+	switch (reboot_mode) {
+	case REBOOT_SOFT:
+		reset_mode = OTTO_WDT_MODE_SOFTWARE;
+		break;
+	case REBOOT_WARM:
+		reset_mode = OTTO_WDT_MODE_CPU;
+		break;
+	default:
+		reset_mode = OTTO_WDT_MODE_SOC;
+		break;
+	}
+
+	/* Configure for shortest timeout and wait for reset to occur */
+	v = FIELD_PREP(OTTO_WDT_CTRL_RST_MODE, reset_mode) | OTTO_WDT_CTRL_ENABLE;
+	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	mdelay(3 * otto_wdt_tick_ms(ctrl, 0));
+
+	return 0;
+}
+
+static irqreturn_t otto_wdt_phase1_isr(int irq, void *dev_id)
+{
+	struct otto_wdt_ctrl *ctrl = dev_id;
+
+	iowrite32(OTTO_WDT_INTR_PHASE_1, ctrl->base + OTTO_WDT_REG_INTR);
+	dev_crit(ctrl->dev, "phase 1 timeout\n");
+	watchdog_notify_pretimeout(&ctrl->wdev);
+
+	return IRQ_HANDLED;
+}
+
+static const struct watchdog_ops otto_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = otto_wdt_start,
+	.stop = otto_wdt_stop,
+	.ping = otto_wdt_ping,
+	.set_timeout = otto_wdt_set_timeout,
+	.set_pretimeout = otto_wdt_set_pretimeout,
+	.restart = otto_wdt_restart,
+};
+
+static const struct watchdog_info otto_wdt_info = {
+	.identity = "Realtek Otto watchdog timer",
+	.options = WDIOF_KEEPALIVEPING |
+		WDIOF_MAGICCLOSE |
+		WDIOF_SETTIMEOUT |
+		WDIOF_PRETIMEOUT,
+};
+
+static void otto_wdt_clock_action(void *data)
+{
+	clk_disable_unprepare(data);
+}
+
+static int otto_wdt_probe_clk(struct otto_wdt_ctrl *ctrl)
+{
+	struct clk *clk = devm_clk_get(ctrl->dev, NULL);
+	int ret;
+
+	if (IS_ERR(clk))
+		return dev_err_probe(ctrl->dev, PTR_ERR(clk), "Failed to get clock\n");
+
+	ret = clk_prepare_enable(clk);
+	if (ret)
+		return dev_err_probe(ctrl->dev, ret, "Failed to enable clock\n");
+
+	ret = devm_add_action_or_reset(ctrl->dev, otto_wdt_clock_action, clk);
+	if (ret)
+		return ret;
+
+	ctrl->clk_rate_khz = clk_get_rate(clk) / 1000;
+	if (ctrl->clk_rate_khz == 0)
+		return dev_err_probe(ctrl->dev, -ENXIO, "Failed to get clock rate\n");
+
+	return 0;
+}
+
+static int otto_wdt_probe_reset_mode(struct otto_wdt_ctrl *ctrl)
+{
+	static const char *mode_property = "realtek,reset-mode";
+	const struct fwnode_handle *node = ctrl->dev->fwnode;
+	int mode_count;
+	u32 mode;
+	u32 v;
+
+	if (!node)
+		return -ENXIO;
+
+	mode_count = fwnode_property_string_array_count(node, mode_property);
+	if (mode_count < 0)
+		return mode_count;
+	else if (mode_count == 0)
+		return 0;
+	else if (mode_count != 1)
+		return -EINVAL;
+
+	if (fwnode_property_match_string(node, mode_property, "soc") == 0)
+		mode = OTTO_WDT_MODE_SOC;
+	else if (fwnode_property_match_string(node, mode_property, "cpu") == 0)
+		mode = OTTO_WDT_MODE_CPU;
+	else if (fwnode_property_match_string(node, mode_property, "software") == 0)
+		mode = OTTO_WDT_MODE_SOFTWARE;
+	else
+		return -EINVAL;
+
+	v = ioread32(ctrl->base + OTTO_WDT_REG_CTRL);
+	v &= ~OTTO_WDT_CTRL_RST_MODE;
+	v |= FIELD_PREP(OTTO_WDT_CTRL_RST_MODE, mode);
+	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	return 0;
+}
+
+static int otto_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct otto_wdt_ctrl *ctrl;
+	unsigned int max_tick_ms;
+	int ret;
+
+	ctrl = devm_kzalloc(dev, sizeof(*ctrl), GFP_KERNEL);
+	if (!ctrl)
+		return -ENOMEM;
+
+	ctrl->dev = dev;
+	ctrl->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(ctrl->base))
+		return PTR_ERR(ctrl->base);
+
+	/* Clear any old interrupts and reset initial state */
+	iowrite32(OTTO_WDT_INTR_PHASE_1 | OTTO_WDT_INTR_PHASE_2,
+			ctrl->base + OTTO_WDT_REG_INTR);
+	iowrite32(OTTO_WDT_CTRL_DEFAULT, ctrl->base + OTTO_WDT_REG_CTRL);
+
+	ret = otto_wdt_probe_clk(ctrl);
+	if (ret)
+		return ret;
+
+	ctrl->irq_phase1 = platform_get_irq_byname(pdev, "phase1");
+	if (ctrl->irq_phase1 < 0)
+		return ctrl->irq_phase1;
+
+	ret = devm_request_irq(dev, ctrl->irq_phase1, otto_wdt_phase1_isr, 0,
+			"realtek-otto-wdt", ctrl);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to get IRQ for phase1\n");
+
+	ret = otto_wdt_probe_reset_mode(ctrl);
+	if (ret)
+		return dev_err_probe(dev, ret, "Invalid reset mode specified\n");
+
+	ctrl->wdev.parent = dev;
+	ctrl->wdev.info = &otto_wdt_info;
+	ctrl->wdev.ops = &otto_wdt_ops;
+
+	/*
+	 * Since pretimeout cannot be disabled, min. timeout is twice the
+	 * subsystem resolution. Max. timeout is ca. 43s at a bus clock of 200MHz.
+	 */
+	ctrl->wdev.min_timeout = 2;
+	max_tick_ms = otto_wdt_tick_ms(ctrl, OTTO_WDT_PRESCALE_MAX);
+	ctrl->wdev.max_hw_heartbeat_ms = max_tick_ms * OTTO_WDT_TIMEOUT_TICKS_MAX;
+	ctrl->wdev.timeout = min(30U, ctrl->wdev.max_hw_heartbeat_ms / 1000);
+
+	watchdog_set_drvdata(&ctrl->wdev, ctrl);
+	watchdog_init_timeout(&ctrl->wdev, 0, dev);
+	watchdog_stop_on_reboot(&ctrl->wdev);
+	watchdog_set_restart_priority(&ctrl->wdev, 128);
+
+	ret = otto_wdt_determine_timeouts(&ctrl->wdev, ctrl->wdev.timeout, 1);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to set timeout\n");
+
+	return devm_watchdog_register_device(dev, &ctrl->wdev);
+}
+
+static const struct of_device_id otto_wdt_ids[] = {
+	{ .compatible = "realtek,rtl8380-wdt" },
+	{ .compatible = "realtek,rtl8390-wdt" },
+	{ .compatible = "realtek,rtl9300-wdt" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, otto_wdt_ids);
+
+static struct platform_driver otto_wdt_driver = {
+	.probe = otto_wdt_probe,
+	.driver = {
+		.name = "realtek-otto-watchdog",
+		.of_match_table	= otto_wdt_ids,
+	},
+};
+module_platform_driver(otto_wdt_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Sander Vanheule <sander@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Realtek Otto watchdog timer driver");
-- 
2.33.1