watchdog: Add Nuvoton NPCM watchdog driver

The Nuvoton NPCM750 has a watchdog implemented as a single register
inside the timer peripheral.

This driver exposes that watchdog as a standard watchdog device with
coarse timeout intervals, limited by the combination of prescaler and
counter that is provided by the hardware. The calculation is taken from
the Nuvoton vendor tree.

The watchdog is left running if a bootloader had it going. The rate is
the one specified in the device tree, or the default value (obtained
from the datasheet).

There is a pre-timeout IRQ that is wired up. This timeout always occurs
1024 clocks before the timeout.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/Kconfig

@@ -514,6 +514,17 @@ config COH901327_WATCHDOG
 	  This watchdog is used to reset the system and thus cannot be
 	  compiled as a module.
 
+config NPCM7XX_WATCHDOG
+	bool "Nuvoton NPCM750 watchdog"
+	depends on ARCH_NPCM || COMPILE_TEST
+	default y if ARCH_NPCM750
+	select WATCHDOG_CORE
+	help
+	  Say Y here to include Watchdog timer support for the
+	  watchdog embedded into the NPCM7xx.
+	  This watchdog is used to reset the system and thus cannot be
+	  compiled as a module.
+
 config TWL4030_WATCHDOG
 	tristate "TWL4030 Watchdog"
 	depends on TWL4030_CORE

drivers/watchdog/Makefile

@@ -61,6 +61,7 @@ obj-$(CONFIG_ORION_WATCHDOG) += orion_wdt.o
 obj-$(CONFIG_SUNXI_WATCHDOG) += sunxi_wdt.o
 obj-$(CONFIG_RN5T618_WATCHDOG) += rn5t618_wdt.o
 obj-$(CONFIG_COH901327_WATCHDOG) += coh901327_wdt.o
+obj-$(CONFIG_NPCM7XX_WATCHDOG) += npcm_wdt.o
 obj-$(CONFIG_STMP3XXX_RTC_WATCHDOG) += stmp3xxx_rtc_wdt.o
 obj-$(CONFIG_NUC900_WATCHDOG) += nuc900_wdt.o
 obj-$(CONFIG_TS4800_WATCHDOG) += ts4800_wdt.o

drivers/watchdog/npcm_wdt.c

@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018 Nuvoton Technology corporation.
+// Copyright (c) 2018 IBM Corp.
+
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/watchdog.h>
+
+#define NPCM_WTCR	0x1C
+
+#define NPCM_WTCLK	(BIT(10) | BIT(11))	/* Clock divider */
+#define NPCM_WTE	BIT(7)			/* Enable */
+#define NPCM_WTIE	BIT(6)			/* Enable irq */
+#define NPCM_WTIS	(BIT(4) | BIT(5))	/* Interval selection */
+#define NPCM_WTIF	BIT(3)			/* Interrupt flag*/
+#define NPCM_WTRF	BIT(2)			/* Reset flag */
+#define NPCM_WTRE	BIT(1)			/* Reset enable */
+#define NPCM_WTR	BIT(0)			/* Reset counter */
+
+/*
+ * Watchdog timeouts
+ *
+ * 170     msec:    WTCLK=01 WTIS=00     VAL= 0x400
+ * 670     msec:    WTCLK=01 WTIS=01     VAL= 0x410
+ * 1360    msec:    WTCLK=10 WTIS=00     VAL= 0x800
+ * 2700    msec:    WTCLK=01 WTIS=10     VAL= 0x420
+ * 5360    msec:    WTCLK=10 WTIS=01     VAL= 0x810
+ * 10700   msec:    WTCLK=01 WTIS=11     VAL= 0x430
+ * 21600   msec:    WTCLK=10 WTIS=10     VAL= 0x820
+ * 43000   msec:    WTCLK=11 WTIS=00     VAL= 0xC00
+ * 85600   msec:    WTCLK=10 WTIS=11     VAL= 0x830
+ * 172000  msec:    WTCLK=11 WTIS=01     VAL= 0xC10
+ * 687000  msec:    WTCLK=11 WTIS=10     VAL= 0xC20
+ * 2750000 msec:    WTCLK=11 WTIS=11     VAL= 0xC30
+ */
+
+struct npcm_wdt {
+	struct watchdog_device  wdd;
+	void __iomem		*reg;
+};
+
+static inline struct npcm_wdt *to_npcm_wdt(struct watchdog_device *wdd)
+{
+	return container_of(wdd, struct npcm_wdt, wdd);
+}
+
+static int npcm_wdt_ping(struct watchdog_device *wdd)
+{
+	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
+	u32 val;
+
+	val = readl(wdt->reg);
+	writel(val | NPCM_WTR, wdt->reg);
+
+	return 0;
+}
+
+static int npcm_wdt_start(struct watchdog_device *wdd)
+{
+	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
+	u32 val;
+
+	if (wdd->timeout < 2)
+		val = 0x800;
+	else if (wdd->timeout < 3)
+		val = 0x420;
+	else if (wdd->timeout < 6)
+		val = 0x810;
+	else if (wdd->timeout < 11)
+		val = 0x430;
+	else if (wdd->timeout < 22)
+		val = 0x820;
+	else if (wdd->timeout < 44)
+		val = 0xC00;
+	else if (wdd->timeout < 87)
+		val = 0x830;
+	else if (wdd->timeout < 173)
+		val = 0xC10;
+	else if (wdd->timeout < 688)
+		val = 0xC20;
+	else
+		val = 0xC30;
+
+	val |= NPCM_WTRE | NPCM_WTE | NPCM_WTR | NPCM_WTIE;
+
+	writel(val, wdt->reg);
+
+	return 0;
+}
+
+static int npcm_wdt_stop(struct watchdog_device *wdd)
+{
+	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
+
+	writel(0, wdt->reg);
+
+	return 0;
+}
+
+
+static int npcm_wdt_set_timeout(struct watchdog_device *wdd,
+				unsigned int timeout)
+{
+	if (timeout < 2)
+		wdd->timeout = 1;
+	else if (timeout < 3)
+	      wdd->timeout = 2;
+	else if (timeout < 6)
+	      wdd->timeout = 5;
+	else if (timeout < 11)
+	      wdd->timeout = 10;
+	else if (timeout < 22)
+	      wdd->timeout = 21;
+	else if (timeout < 44)
+	      wdd->timeout = 43;
+	else if (timeout < 87)
+	      wdd->timeout = 86;
+	else if (timeout < 173)
+	      wdd->timeout = 172;
+	else if (timeout < 688)
+	      wdd->timeout = 687;
+	else
+	      wdd->timeout = 2750;
+
+	if (watchdog_active(wdd))
+		npcm_wdt_start(wdd);
+
+	return 0;
+}
+
+static irqreturn_t npcm_wdt_interrupt(int irq, void *data)
+{
+	struct npcm_wdt *wdt = data;
+
+	watchdog_notify_pretimeout(&wdt->wdd);
+
+	return IRQ_HANDLED;
+}
+
+static int npcm_wdt_restart(struct watchdog_device *wdd,
+			    unsigned long action, void *data)
+{
+	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
+
+	writel(NPCM_WTR | NPCM_WTRE | NPCM_WTE, wdt->reg);
+	udelay(1000);
+
+	return 0;
+}
+
+static bool npcm_is_running(struct watchdog_device *wdd)
+{
+	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
+
+	return readl(wdt->reg) & NPCM_WTE;
+}
+
+static const struct watchdog_info npcm_wdt_info = {
+	.identity	= KBUILD_MODNAME,
+	.options	= WDIOF_SETTIMEOUT
+			| WDIOF_KEEPALIVEPING
+			| WDIOF_MAGICCLOSE,
+};
+
+static const struct watchdog_ops npcm_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = npcm_wdt_start,
+	.stop = npcm_wdt_stop,
+	.ping = npcm_wdt_ping,
+	.set_timeout = npcm_wdt_set_timeout,
+	.restart = npcm_wdt_restart,
+};
+
+static int npcm_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct npcm_wdt *wdt;
+	struct resource *res;
+	int irq;
+	int ret;
+
+	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
+	if (!wdt)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	wdt->reg = devm_ioremap_resource(dev, res);
+	if (IS_ERR(wdt->reg))
+		return PTR_ERR(wdt->reg);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	wdt->wdd.info = &npcm_wdt_info;
+	wdt->wdd.ops = &npcm_wdt_ops;
+	wdt->wdd.min_timeout = 1;
+	wdt->wdd.max_timeout = 2750;
+	wdt->wdd.parent = dev;
+
+	wdt->wdd.timeout = 86;
+	watchdog_init_timeout(&wdt->wdd, 0, dev);
+
+	/* Ensure timeout is able to be represented by the hardware */
+	npcm_wdt_set_timeout(&wdt->wdd, wdt->wdd.timeout);
+
+	if (npcm_is_running(&wdt->wdd)) {
+		/* Restart with the default or device-tree specified timeout */
+		npcm_wdt_start(&wdt->wdd);
+		set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
+	}
+
+	ret = devm_request_irq(dev, irq, npcm_wdt_interrupt, 0,
+			       "watchdog", wdt);
+	if (ret)
+		return ret;
+
+	ret = devm_watchdog_register_device(dev, &wdt->wdd);
+	if (ret) {
+		dev_err(dev, "failed to register watchdog\n");
+		return ret;
+	}
+
+	dev_info(dev, "NPCM watchdog driver enabled\n");
+
+	return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id npcm_wdt_match[] = {
+	{.compatible = "nuvoton,npcm750-wdt"},
+	{},
+};
+MODULE_DEVICE_TABLE(of, npcm_wdt_match);
+#endif
+
+static struct platform_driver npcm_wdt_driver = {
+	.probe		= npcm_wdt_probe,
+	.driver		= {
+		.name	= "npcm-wdt",
+		.of_match_table = of_match_ptr(npcm_wdt_match),
+	},
+};
+module_platform_driver(npcm_wdt_driver);
+
+MODULE_AUTHOR("Joel Stanley");
+MODULE_DESCRIPTION("Watchdog driver for NPCM");
+MODULE_LICENSE("GPL v2");