[PATCH v2] watchdog: qcom_wdt: set WDOG_HW_RUNNING bit when appropriate

[Robert Marko <robert.marko@sartura.hr>]

If the watchdog hardware is enabled/running during boot, e.g.
due to a boot loader configuring it, we must tell the
watchdog framework about this fact so that it can ping the
watchdog until userspace opens the device and takes over
control.

Do so using the WDOG_HW_RUNNING flag that exists for exactly
that use-case.

Given the watchdog driver core doesn't know what timeout was
originally set by whoever started the watchdog (boot loader),
we make sure to update the timeout in the hardware according
to what the watchdog core thinks it is.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Cc: Luka Perkov <luka.perkov@sartura.hr>
---
Changes in v2:
* Correct authorship

 drivers/watchdog/qcom-wdt.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
index ab7465d186fd..28c93a918e38 100644
--- a/drivers/watchdog/qcom-wdt.c
+++ b/drivers/watchdog/qcom-wdt.c
@@ -152,6 +152,13 @@ static int qcom_wdt_restart(struct watchdog_device *wdd, unsigned long action,
 	return 0;
 }
 
+static int qcom_wdt_is_running(struct watchdog_device *wdd)
+{
+	struct qcom_wdt *wdt = to_qcom_wdt(wdd);
+
+	return (readl(wdt_addr(wdt, WDT_EN)) & 1);
+}
+
 static const struct watchdog_ops qcom_wdt_ops = {
 	.start		= qcom_wdt_start,
 	.stop		= qcom_wdt_stop,
@@ -294,6 +301,21 @@ static int qcom_wdt_probe(struct platform_device *pdev)
 	wdt->wdd.timeout = min(wdt->wdd.max_timeout, 30U);
 	watchdog_init_timeout(&wdt->wdd, 0, dev);
 
+	if (qcom_wdt_is_running(&wdt->wdd)) {
+		/*
+		 * Make sure to apply timeout from watchdog core, taking
+		 * the prescaler of this driver here into account (the
+		 * boot loader might be using a different prescaler).
+		 *
+		 * To avoid spurious resets because of different scaling,
+		 * we first disable the watchdog, set the new prescaler
+		 * and timeout, and then re-enable the watchdog.
+		 */
+		qcom_wdt_stop(&wdt->wdd);
+		qcom_wdt_start(&wdt->wdd);
+		set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
+	}
+
 	ret = devm_watchdog_register_device(dev, &wdt->wdd);
 	if (ret)
 		return ret;
-- 
2.28.0