watchdog: add watchdog driver for MediaTek MT7620 SoC

This patch adds watchdog support for the Mediatek MT7620 SoC

Reviewed-by: Stefan Roese <[e-mail]>
Reviewed-by: Jagan Teki <[e-mail]>
Signed-off-by: Weijie Gao <[e-mail]>

drivers/watchdog/Kconfig

···
 	help
 	  Select this to enable mpc8xx watchdog timer
 
+config WDT_MT7620
+	bool "MediaTek MT7620 watchdog timer support"
+	depends on WDT && SOC_MT7620
+	help
+	  Select this to enable watchdog timer on MediaTek MT7620 and earlier
+	  SoC chips.
+
 config WDT_MT7621
 	bool "MediaTek MT7621 watchdog timer support"
 	depends on WDT && SOC_MT7628

drivers/watchdog/Makefile

···
 obj-$(CONFIG_WDT_ORION) += orion_wdt.o
 obj-$(CONFIG_WDT_CDNS) += cdns_wdt.o
 obj-$(CONFIG_WDT_MPC8xx) += mpc8xx_wdt.o
+obj-$(CONFIG_WDT_MT7620) += mt7620_wdt.o
 obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o
 obj-$(CONFIG_WDT_MTK) += mtk_wdt.o
 obj-$(CONFIG_WDT_OCTEONTX) += octeontx_wdt.o

drivers/watchdog/mt7620_wdt.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 MediaTek Inc.
+ *
+ * Author:  Weijie Gao <[e-mail]>
+ *
+ * Watchdog timer for MT7620 and earlier SoCs
+ */
+
+#include <div64.h>
+#include <dm.h>
+#include <reset.h>
+#include <wdt.h>
+#include <linux/bitops.h>
+#include <linux/io.h>
+
+struct mt7620_wdt {
+	void __iomem *regs;
+	u64 timeout;
+};
+
+#define TIMER_FREQ			40000000
+#define TIMER_MASK			0xffff
+#define TIMER_PRESCALE			65536
+
+#define TIMER_LOAD			0x00
+#define TIMER_CTL			0x08
+
+#define TIMER_ENABLE			BIT(7)
+#define TIMER_MODE_SHIFT		4
+#define   TIMER_MODE_WDT		3
+#define TIMER_PRESCALE_SHIFT		0
+#define   TIMER_PRESCALE_65536		15
+
+static void mt7620_wdt_ping(struct mt7620_wdt *priv)
+{
+	u64 val;
+
+	val = (TIMER_FREQ / TIMER_PRESCALE) * priv->timeout;
+	do_div(val, 1000);
+
+	if (val > TIMER_MASK)
+		val = TIMER_MASK;
+
+	writel(val, priv->regs + TIMER_LOAD);
+}
+
+static int mt7620_wdt_start(struct udevice *dev, u64 ms, ulong flags)
+{
+	struct mt7620_wdt *priv = dev_get_priv(dev);
+
+	priv->timeout = ms;
+	mt7620_wdt_ping(priv);
+
+	writel(TIMER_ENABLE | (TIMER_MODE_WDT << TIMER_MODE_SHIFT) |
+	       (TIMER_PRESCALE_65536 << TIMER_PRESCALE_SHIFT),
+	       priv->regs + TIMER_CTL);
+
+	return 0;
+}
+
+static int mt7620_wdt_stop(struct udevice *dev)
+{
+	struct mt7620_wdt *priv = dev_get_priv(dev);
+
+	mt7620_wdt_ping(priv);
+
+	clrbits_32(priv->regs + TIMER_CTL, TIMER_ENABLE);
+
+	return 0;
+}
+
+static int mt7620_wdt_reset(struct udevice *dev)
+{
+	struct mt7620_wdt *priv = dev_get_priv(dev);
+
+	mt7620_wdt_ping(priv);
+
+	return 0;
+}
+
+static int mt7620_wdt_expire_now(struct udevice *dev, ulong flags)
+{
+	struct mt7620_wdt *priv = dev_get_priv(dev);
+
+	mt7620_wdt_start(dev, 1, flags);
+
+	/*
+	 * 0 will disable the timer directly, a positive number must be used
+	 * instead. Since the timer is a countdown timer, 1 (tick) is used.
+	 *
+	 * For a timer with input clock = 40MHz, 1 timer tick is short
+	 * enough to trigger a timeout immediately.
+	 *
+	 * Restore prescale to 1, and load timer with 1 to trigger timeout.
+	 */
+	writel(TIMER_ENABLE | (TIMER_MODE_WDT << TIMER_MODE_SHIFT),
+	       priv->regs + TIMER_CTL);
+	writel(1, priv->regs + TIMER_LOAD);
+
+	return 0;
+}
+
+static int mt7620_wdt_probe(struct udevice *dev)
+{
+	struct mt7620_wdt *priv = dev_get_priv(dev);
+	struct reset_ctl reset_wdt;
+	int ret;
+
+	ret = reset_get_by_index(dev, 0, &reset_wdt);
+	if (!ret)
+		reset_deassert(&reset_wdt);
+
+	priv->regs = dev_remap_addr(dev);
+	if (!priv->regs)
+		return -EINVAL;
+
+	mt7620_wdt_stop(dev);
+
+	return 0;
+}
+
+static const struct wdt_ops mt7620_wdt_ops = {
+	.start = mt7620_wdt_start,
+	.reset = mt7620_wdt_reset,
+	.stop = mt7620_wdt_stop,
+	.expire_now = mt7620_wdt_expire_now,
+};
+
+static const struct udevice_id mt7620_wdt_ids[] = {
+	{ .compatible = "mediatek,mt7620-wdt" },
+	{}
+};
+
+U_BOOT_DRIVER(mt7620_wdt) = {
+	.name = "mt7620_wdt",
+	.id = UCLASS_WDT,
+	.of_match = mt7620_wdt_ids,
+	.probe = mt7620_wdt_probe,
+	.priv_auto = sizeof(struct mt7620_wdt),
+	.ops = &mt7620_wdt_ops,
+};