watchdog: renesas_wdt: support handover from bootloader

Support an already running watchdog by checking its enable bit and set
up the status accordingly before registering the device.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200908095615.31376-1-wsa+renesas@sang-engineering.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/renesas_wdt.c

@@ -194,6 +194,7 @@ static int rwdt_probe(struct platform_device *pdev)
 	struct clk *clk;
 	unsigned long clks_per_sec;
 	int ret, i;
+	u8 csra;
 
 	if (rwdt_blacklisted(dev))
 		return -ENODEV;
@@ -213,8 +214,8 @@ static int rwdt_probe(struct platform_device *pdev)
 	pm_runtime_enable(dev);
 	pm_runtime_get_sync(dev);
 	priv->clk_rate = clk_get_rate(clk);
-	priv->wdev.bootstatus = (readb_relaxed(priv->base + RWTCSRA) &
-				RWTCSRA_WOVF) ? WDIOF_CARDRESET : 0;
+	csra = readb_relaxed(priv->base + RWTCSRA);
+	priv->wdev.bootstatus = csra & RWTCSRA_WOVF ? WDIOF_CARDRESET : 0;
 	pm_runtime_put(dev);
 
 	if (!priv->clk_rate) {
@@ -252,6 +253,13 @@ static int rwdt_probe(struct platform_device *pdev)
 	/* This overrides the default timeout only if DT configuration was found */
 	watchdog_init_timeout(&priv->wdev, 0, dev);
 
+	/* Check if FW enabled the watchdog */
+	if (csra & RWTCSRA_TME) {
+		/* Ensure properly initialized dividers */
+		rwdt_start(&priv->wdev);
+		set_bit(WDOG_HW_RUNNING, &priv->wdev.status);
+	}
+
 	ret = watchdog_register_device(&priv->wdev);
 	if (ret < 0)
 		goto out_pm_disable;