[PATCH] at91sam9_wdt: Allow watchdog to reset device at early boot

[Timo Kokkonen]

By default the driver will start a kernel timer which keeps on kicking
the watchdog HW until user space has opened the watchdog
device. Usually this is desirable as the watchdog HW is running by
default and the user space may not have any watchdog daemon running at
all.

However, on production systems it may be mandatory that also early
crashes and lockups will lead to a watchdog reset, even if they happen
before the user space has opened the watchdog device.

To resolve the issue, add a new device tree property
"enable-early-reset" which will prevent the kernel timer from pinging
the watchdog HW on behalf of user space. The default is still to use
kernel timer, but more strict behavior can be enabled via the device
tree property.

Signed-off-by: Timo Kokkonen <timo.kokkonen at offcode.fi>
---
 Documentation/devicetree/bindings/watchdog/atmel-wdt.txt | 4 ++++
 drivers/watchdog/at91sam9_wdt.c                          | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
index f90e294..a0b7b75 100644
--- a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
+++ b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
@@ -28,6 +28,10 @@ Optional properties:
 	entering idle state.
 - atmel,dbg-halt : Should be present if you want to stop the watchdog when
 	entering debug state.
+- enable-early-reset : Should be present if you want to let the
+	watchdog timer to expire even before user space has opened the
+	device. If not set, a kernel timer will keep on pinging the
+	watchdog until it is opened.
 
 Example:
 	watchdog at fffffd40 {
diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
index 489729b..78b1977 100644
--- a/drivers/watchdog/at91sam9_wdt.c
+++ b/drivers/watchdog/at91sam9_wdt.c
@@ -89,6 +89,7 @@ struct at91wdt {
 	u32 mr_mask;
 	unsigned long heartbeat;	/* WDT heartbeat in jiffies */
 	bool nowayout;
+	bool no_early_timer;
 	unsigned int irq;
 };
 
@@ -122,7 +123,7 @@ static void at91_ping(unsigned long data)
 {
 	struct at91wdt *wdt = (struct at91wdt *)data;
 	if (time_before(jiffies, wdt->next_heartbeat) ||
-	    !watchdog_active(&wdt->wdd)) {
+		(!watchdog_active(&wdt->wdd) && !wdt->no_early_timer)) {
 		at91_wdt_reset(wdt);
 		mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
 	} else {
@@ -316,6 +317,9 @@ static int of_at91wdt_init(struct device_node *np, struct at91wdt *wdt)
 
 	wdt->mr |= max | ((max - min) << 16);
 
+	if (of_property_read_bool(np, "enable-early-reset"))
+		wdt->no_early_timer = 1;
+
 	return 0;
 }
 #else
-- 
2.1.0