[PATCH] watchdog: fix watchdog_set_timeout breakage for drivers like imxwd

[Ahmad Fatoum]

Commit 0b944fce55f4 ("watchdog: permit `wd 0` for non-stoppable, but
inactive, watchdogs") silently broke use of non-stoppable, but inactive,
watchdogs altogether. Because those always had watchdog_hw_running
evaluating to false, it early exited without a chance to ever actually
set the timeout (and for watchdog_hw_running to evaluate to != false).

This results in following watchdog drivers being broken in v2020.08.0:

 - imxwd
 - f71808e_wdt
 - at91sam9_wdt

Fixes: 0b944fce55f4 ("watchdog: permit `wd 0` for non-stoppable, but inactive, watchdogs")
Reported-by: Bastian Krause <bst at pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
Please apply to master (and to v2020.08.1?).
---
 drivers/watchdog/wd_core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/wd_core.c b/drivers/watchdog/wd_core.c
index ab1dcaa40a3a..4247288dbd0a 100644
--- a/drivers/watchdog/wd_core.c
+++ b/drivers/watchdog/wd_core.c
@@ -45,12 +45,11 @@ 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);
+	if (ret == -ENOSYS && watchdog_hw_running(wd) == false)
+		return 0;
 	if (ret)
 		return ret;
 
-- 
2.28.0