watchdog: mtk: add disable_wdt_extrst support

In some cases, we may need watchdog just to trigger an
internal soc reset without sending any output signal.

Provide a disable_wdt_extrst parameter for configuration.
We can disable or enable it just by configuring dts.
Signed-off-by: Fengquan Chen <fengquan.chen@mediatek.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210914123454.32603-3-Fengquan.Chen@mediatek.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/mtk_wdt.c

@@ -65,6 +65,7 @@ struct mtk_wdt_dev {
 	void __iomem *wdt_base;
 	spinlock_t lock; /* protects WDT_SWSYSRST reg */
 	struct reset_controller_dev rcdev;
+	bool disable_wdt_extrst;
 };
 
 struct mtk_wdt_data {
@@ -256,6 +257,8 @@ static int mtk_wdt_start(struct watchdog_device *wdt_dev)
 		reg |= (WDT_MODE_IRQ_EN | WDT_MODE_DUAL_EN);
 	else
 		reg &= ~(WDT_MODE_IRQ_EN | WDT_MODE_DUAL_EN);
+	if (mtk_wdt->disable_wdt_extrst)
+		reg &= ~WDT_MODE_EXRST_EN;
 	reg |= (WDT_MODE_EN | WDT_MODE_KEY);
 	iowrite32(reg, wdt_base + WDT_MODE);
 
@@ -381,6 +384,10 @@ static int mtk_wdt_probe(struct platform_device *pdev)
 		if (err)
 			return err;
 	}
+
+	mtk_wdt->disable_wdt_extrst =
+		of_property_read_bool(dev->of_node, "mediatek,disable-extrst");
+
 	return 0;
 }