[cip-dev] [PATCH 07/10] watchdog: change watchdog_need_worker logic

[mosipov@ilbers.de (Maxim Yu. Osipov)]

From: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

Backport from kernel.org, upstream commit 3fbfe9264756

If the driver indicates that the watchdog is running, the framework
should feed it until userspace opens the device, regardless of whether
the driver has set max_hw_heartbeat_ms.

This patch only affects the case where wdd->max_hw_heartbeat_ms is
zero, wdd->timeout is non-zero, the watchdog is not active and the
hardware device is running (*):

- If wdd->timeout is zero, watchdog_need_worker() returns false both
before and after this patch, and watchdog_next_keepalive() is not
called.

- If watchdog_active(wdd), the return value from watchdog_need_worker
is also the same as before (namely, hm && t > hm). Hence in that case,
watchdog_next_keepalive() is only called if hm == max_hw_heartbeat_ms
is non-zero, so the change to min_not_zero there is a no-op.

- If the watchdog is not active and the device is not running, we
return false from watchdog_need_worker just as before.

That leaves the watchdog_hw_running(wdd) && !watchdog_active(wdd) &&
wdd->timeout case. Again, it's easy to see that if
wdd->max_hw_heartbeat_ms is non-zero, we return true from
watchdog_need_worker with and without this patch, and the logic in
watchdog_next_keepalive is unchanged. Finally, if
wdd->max_hw_heartbeat_ms is 0, we used to end up in the
cancel_delayed_work branch, whereas with this patch we end up
scheduling a ping timeout_ms/2 from now.

(*) This should imply that no current kernel drivers are affected,
since the only drivers which explicitly set WDOG_HW_RUNNING are
imx2_wdt.c and dw_wdt.c, both of which also provide a non-zero value
for max_hw_heartbeat_ms. The watchdog core also sets WDOG_HW_RUNNING,
but only when the driver doesn't provide ->stop, in which case it
must, according to Documentation/watchdog/watchdog-kernel-api.txt, set
max_hw_heartbeat_ms.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
[mosipov at ilbers.de backported to 4.4.y]
Signed-off-by: Maxim Yu. Osipov <mosipov@ilbers.de>
---
 drivers/watchdog/watchdog_dev.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 2eca04d869d9..e3eacf27b1e7 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -67,9 +67,13 @@ static inline bool watchdog_need_worker(struct watchdog_device *wdd)
 	 *   thus is aware that the framework supports generating heartbeat
 	 *   requests.
 	 * - Userspace requests a longer timeout than the hardware can handle.
+	 *
+	 * Alternatively, if userspace has not opened the watchdog
+	 * device, we take care of feeding the watchdog if it is
+	 * running.
 	 */
-	return hm && ((watchdog_active(wdd) && t > hm) ||
-		      (t && !watchdog_active(wdd) && watchdog_hw_running(wdd)));
+	return (hm && watchdog_active(wdd) && t > hm) ||
+		(t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
 }
 
 static long watchdog_next_keepalive(struct watchdog_device *wdd)
@@ -81,7 +85,7 @@ static long watchdog_next_keepalive(struct watchdog_device *wdd)
 	unsigned int hw_heartbeat_ms;
 
 	virt_timeout = wdd->last_keepalive + msecs_to_jiffies(timeout_ms);
-	hw_heartbeat_ms = min(timeout_ms, wdd->max_hw_heartbeat_ms);
+	hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
 	keepalive_interval = msecs_to_jiffies(hw_heartbeat_ms / 2);
 
 	if (!watchdog_active(wdd))
-- 
2.11.0