watchdog: qcom: register a restart notifier

The WDT's BITE_TIME warm-reset behavior can be leveraged as a last
resort mechanism for triggering chip reset.  Usually, other restart
methods (such as PS_HOLD) are preferrable for issuing a more complete
reset of the chip.  As such, keep the priority of the watchdog notifier
low.
Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/qcom-wdt.c

@@ -11,11 +11,13 @@
  *
  */
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/reboot.h>
 #include <linux/watchdog.h>
 
 #define WDT_RST		0x0
@@ -26,6 +28,7 @@ struct qcom_wdt {
 	struct watchdog_device	wdd;
 	struct clk		*clk;
 	unsigned long		rate;
+	struct notifier_block	restart_nb;
 	void __iomem		*base;
 };
 
@@ -84,6 +87,32 @@ static const struct watchdog_info qcom_wdt_info = {
 	.identity	= KBUILD_MODNAME,
 };
 
+static int qcom_wdt_restart(struct notifier_block *nb, unsigned long action,
+			    void *data)
+{
+	struct qcom_wdt *wdt = container_of(nb, struct qcom_wdt, restart_nb);
+	u32 timeout;
+
+	/*
+	 * Trigger watchdog bite:
+	 *    Setup BITE_TIME to be 128ms, and enable WDT.
+	 */
+	timeout = 128 * wdt->rate / 1000;
+
+	writel(0, wdt->base + WDT_EN);
+	writel(1, wdt->base + WDT_RST);
+	writel(timeout, wdt->base + WDT_BITE_TIME);
+	writel(1, wdt->base + WDT_EN);
+
+	/*
+	 * Actually make sure the above sequence hits hardware before sleeping.
+	 */
+	wmb();
+
+	msleep(150);
+	return NOTIFY_DONE;
+}
+
 static int qcom_wdt_probe(struct platform_device *pdev)
 {
 	struct qcom_wdt *wdt;
@@ -147,6 +176,14 @@ static int qcom_wdt_probe(struct platform_device *pdev)
 		goto err_clk_unprepare;
 	}
 
+	/*
+	 * WDT restart notifier has priority 0 (use as a last resort)
+	 */
+	wdt->restart_nb.notifier_call = qcom_wdt_restart;
+	ret = register_restart_handler(&wdt->restart_nb);
+	if (ret)
+		dev_err(&pdev->dev, "failed to setup restart handler\n");
+
 	platform_set_drvdata(pdev, wdt);
 	return 0;
 
@@ -159,6 +196,7 @@ static int qcom_wdt_remove(struct platform_device *pdev)
 {
 	struct qcom_wdt *wdt = platform_get_drvdata(pdev);
 
+	unregister_restart_handler(&wdt->restart_nb);
 	watchdog_unregister_device(&wdt->wdd);
 	clk_disable_unprepare(wdt->clk);
 	return 0;