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>

1 files changed, 38 insertions, 0 deletions

diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
index 68db322341bc..aa85618c4d03 100644
--- a/drivers/watchdog/qcom-wdt.c
+++ b/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;