wdt: Add MT7621 watchdog driver

This patch adds watchdog support for the Mediatek MT7621 SoC. The driver
is loosly based on the Linux kernel version.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
[fixed merge conflict in drivers/watchdog/Kconfig]
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

drivers/watchdog/Kconfig

@@ -128,4 +128,12 @@ config WDT_AT91
 config AT91_HW_WDT_TIMEOUT
 	bool "AT91 watchdog timeout specified"
 	depends on WDT_AT91
+
+config WDT_MT7621
+	bool "MediaTek MT7621 watchdog timer support"
+	depends on WDT && ARCH_MT7620
+	help
+	   Select this to enable Ralink / Mediatek watchdog timer,
+	   which can be found on some MediaTek chips.
+
 endmenu

drivers/watchdog/Makefile

@@ -23,3 +23,4 @@ obj-$(CONFIG_BCM2835_WDT)       += bcm2835_wdt.o
 obj-$(CONFIG_WDT_ORION) += orion_wdt.o
 obj-$(CONFIG_WDT_CDNS) += cdns_wdt.o
 obj-$(CONFIG_MPC8xx_WATCHDOG) += mpc8xx_wdt.o
+obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o

drivers/watchdog/mt7621_wdt.c

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Ralink / Mediatek RT288x/RT3xxx/MT76xx built-in hardware watchdog timer
+ *
+ * Copyright (C) 2018 Stefan Roese <sr@denx.de>
+ *
+ * Based on the Linux driver version which is:
+ *   Copyright (C) 2011 Gabor Juhos <juhosg@openwrt.org>
+ *   Copyright (C) 2013 John Crispin <blogic@openwrt.org>
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <wdt.h>
+#include <linux/io.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+struct mt762x_wdt {
+	void __iomem *regs;
+};
+
+#define TIMER_REG_TMRSTAT		0x00
+#define TIMER_REG_TMR1CTL		0x20
+#define TIMER_REG_TMR1LOAD		0x24
+
+#define TMR1CTL_ENABLE			BIT(7)
+#define TMR1CTL_RESTART			BIT(9)
+#define TMR1CTL_PRESCALE_SHIFT		16
+
+static int mt762x_wdt_ping(struct mt762x_wdt *priv)
+{
+	writel(TMR1CTL_RESTART, priv->regs + TIMER_REG_TMRSTAT);
+
+	return 0;
+}
+
+static int mt762x_wdt_start(struct udevice *dev, u64 ms, ulong flags)
+{
+	struct mt762x_wdt *priv = dev_get_priv(dev);
+
+	/* set the prescaler to 1ms == 1000us */
+	writel(1000 << TMR1CTL_PRESCALE_SHIFT, priv->regs + TIMER_REG_TMR1CTL);
+	writel(ms, priv->regs + TIMER_REG_TMR1LOAD);
+
+	setbits_le32(priv->regs + TIMER_REG_TMR1CTL, TMR1CTL_ENABLE);
+
+	return 0;
+}
+
+static int mt762x_wdt_stop(struct udevice *dev)
+{
+	struct mt762x_wdt *priv = dev_get_priv(dev);
+
+	mt762x_wdt_ping(priv);
+
+	clrbits_le32(priv->regs + TIMER_REG_TMR1CTL, TMR1CTL_ENABLE);
+
+	return 0;
+}
+
+static int mt762x_wdt_reset(struct udevice *dev)
+{
+	struct mt762x_wdt *priv = dev_get_priv(dev);
+
+	mt762x_wdt_ping(priv);
+
+	return 0;
+}
+
+static int mt762x_wdt_probe(struct udevice *dev)
+{
+	struct mt762x_wdt *priv = dev_get_priv(dev);
+
+	priv->regs = dev_remap_addr(dev);
+	if (!priv->regs)
+		return -EINVAL;
+
+	mt762x_wdt_stop(dev);
+
+	return 0;
+}
+
+static const struct wdt_ops mt762x_wdt_ops = {
+	.start = mt762x_wdt_start,
+	.reset = mt762x_wdt_reset,
+	.stop = mt762x_wdt_stop,
+};
+
+static const struct udevice_id mt762x_wdt_ids[] = {
+	{ .compatible = "mediatek,mt7621-wdt" },
+	{}
+};
+
+U_BOOT_DRIVER(mt762x_wdt) = {
+	.name = "mt762x_wdt",
+	.id = UCLASS_WDT,
+	.of_match = mt762x_wdt_ids,
+	.probe = mt762x_wdt_probe,
+	.priv_auto_alloc_size = sizeof(struct mt762x_wdt),
+	.ops = &mt762x_wdt_ops,
+};