[PATCH v2] watchdog: permit `wd 0` for non-stoppable, but inactive, watchdogs

[Ahmad Fatoum]

A watchdog that can't be stopped returns -ENOSYS on set_timeout(0).
If the watchdog supports communicating whether it's running, we could
still allow `wd 0`, if it hasn't been started yet.

Setting device parameter .priority=0 disables a watchdog. One would
expect this to always succeed for a not-running watchdog, but currently
it doesn't, if the driver's set_timeout(0) returns -ENOSYS. With this
fix, this is supported making the user API less surprising.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
v1 -> v2:
  - use watchdog_hw_running helper
---
 drivers/watchdog/wd_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/watchdog/wd_core.c b/drivers/watchdog/wd_core.c
index 34040408f716..72ada91dbf71 100644
--- a/drivers/watchdog/wd_core.c
+++ b/drivers/watchdog/wd_core.c
@@ -45,6 +45,9 @@ int watchdog_set_timeout(struct watchdog *wd, unsigned timeout)
 	if (timeout > wd->timeout_max)
 		return -EINVAL;
 
+	if (watchdog_hw_running(wd) == false)
+		return 0;
+
 	pr_debug("setting timeout on %s to %ds\n", watchdog_name(wd), timeout);
 
 	ret = wd->set_timeout(wd, timeout);
-- 
2.27.0