[PATCH v10 3/3] watchdog: make the device time out at open_deadline when open_timeout is used

[Rasmus Villemoes]

When the watchdog device is not open by userspace, the kernel takes
care of pinging it. When the open_timeout feature is in use, we should
ensure that the hardware fires close to open_timeout seconds after the
kernel has assumed responsibility for the device.

To do this, simply reuse the logic that is already in place for
ensuring the same thing when userspace is responsible for regularly
pinging the device:

- When watchdog_active(wdd), this patch doesn't change anything.

- When !watchdoc_active(wdd), the "virtual timeout" should be taken to
be ->open_deadline". When the open_timeout feature is not used or the
device has been opened at least once, ->open_deadline is KTIME_MAX,
and the arithmetic ends up returning keepalive_interval as we used to.

This has been tested on a Wandboard with various combinations of
open_timeout and timeout-sec properties for the on-board watchdog by
booting with 'init=/bin/sh', timestamping the lines on the serial
console, and comparing the timestamp of the 'imx2-wdt 20bc000.wdog:
timeout nnn sec' line with the timestamp of the 'U-Boot SPL ...'
line (which appears just after reset).

Suggested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
---
 drivers/watchdog/watchdog_dev.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 334b810db2cf..edfb884044e0 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -133,14 +133,15 @@ static ktime_t watchdog_next_keepalive(struct watchdog_device *wdd)
 	ktime_t virt_timeout;
 	unsigned int hw_heartbeat_ms;
 
-	virt_timeout = ktime_add(wd_data->last_keepalive,
-				 ms_to_ktime(timeout_ms));
+	if (watchdog_active(wdd))
+		virt_timeout = ktime_add(wd_data->last_keepalive,
+					 ms_to_ktime(timeout_ms));
+	else
+		virt_timeout = wd_data->open_deadline;
+
 	hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
 	keepalive_interval = ms_to_ktime(hw_heartbeat_ms / 2);
 
-	if (!watchdog_active(wdd))
-		return keepalive_interval;
-
 	/*
 	 * To ensure that the watchdog times out wdd->timeout seconds
 	 * after the most recent ping from userspace, the last
-- 
2.20.1