watchdog: imx2_wdg: Alow ping on suspend

The i.MX watchdog cannot be disabled by software once it has been
enabled. This means that it can't be stopped before suspend.

For systems that enter low power mode this is fine, as the watchdog will
be automatically stopped by hardware in low power mode. Not all i.MX
platforms support low power mode in the mainline kernel. For example the
i.MX7D does not enter low power mode and so will be rebooted 2 minutes
after entering sleep states.

This patch introduces a device tree property "fsl,ping-during-suspend"
that can be used to enable ping on suspend support for these systems.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220127104739.312592-1-alistair@alistair23.me
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: alistair23

drivers/watchdog/imx2_wdt.c

@@ -66,6 +66,7 @@ struct imx2_wdt_device {
 	struct watchdog_device wdog;
 	bool ext_reset;
 	bool clk_is_on;
+	bool no_ping;
 };
 
 static bool nowayout = WATCHDOG_NOWAYOUT;
@@ -312,12 +313,18 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
 
 	wdev->ext_reset = of_property_read_bool(dev->of_node,
 						"fsl,ext-reset-output");
+	/*
+	 * The i.MX7D doesn't support low power mode, so we need to ping the watchdog
+	 * during suspend.
+	 */
+	wdev->no_ping = !of_device_is_compatible(dev->of_node, "fsl,imx7d-wdt");
 	platform_set_drvdata(pdev, wdog);
 	watchdog_set_drvdata(wdog, wdev);
 	watchdog_set_nowayout(wdog, nowayout);
 	watchdog_set_restart_priority(wdog, 128);
 	watchdog_init_timeout(wdog, timeout, dev);
-	watchdog_stop_ping_on_suspend(wdog);
+	if (wdev->no_ping)
+		watchdog_stop_ping_on_suspend(wdog);
 
 	if (imx2_wdt_is_running(wdev)) {
 		imx2_wdt_set_timeout(wdog, wdog->timeout);
@@ -366,9 +373,11 @@ static int __maybe_unused imx2_wdt_suspend(struct device *dev)
 		imx2_wdt_ping(wdog);
 	}
 
-	clk_disable_unprepare(wdev->clk);
+	if (wdev->no_ping) {
+		clk_disable_unprepare(wdev->clk);
 
-	wdev->clk_is_on = false;
+		wdev->clk_is_on = false;
+	}
 
 	return 0;
 }
@@ -380,11 +389,14 @@ static int __maybe_unused imx2_wdt_resume(struct device *dev)
 	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
 	int ret;
 
-	ret = clk_prepare_enable(wdev->clk);
-	if (ret)
-		return ret;
+	if (wdev->no_ping) {
+		ret = clk_prepare_enable(wdev->clk);
 
-	wdev->clk_is_on = true;
+		if (ret)
+			return ret;
+
+		wdev->clk_is_on = true;
+	}
 
 	if (watchdog_active(wdog) && !imx2_wdt_is_running(wdev)) {
 		/*
@@ -407,6 +419,7 @@ static SIMPLE_DEV_PM_OPS(imx2_wdt_pm_ops, imx2_wdt_suspend,
 
 static const struct of_device_id imx2_wdt_dt_ids[] = {
 	{ .compatible = "fsl,imx21-wdt", },
+	{ .compatible = "fsl,imx7d-wdt", },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, imx2_wdt_dt_ids);