Re: [PATCH v2 3/8] watchdog: Introduce WDOG_RUNNING flag

Guenter Roeck
2015-08-15T23:38:33Z

On 08/14/2015 12:04 PM, Uwe Kleine-König wrote:
> Hello Guenter,
>
>> diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
>> index 25b00b878a7b..6a54dc15a556 100644
>> --- a/Documentation/watchdog/watchdog-kernel-api.txt
>> +++ b/Documentation/watchdog/watchdog-kernel-api.txt
>> [...]
>> @@ -193,9 +194,12 @@ they are supported. These optional routines/operations are:
>> The status bits should (preferably) be set with the set_bit and clear_bit alike
>> bit-operations. The status bits that are defined are:
>> * WDOG_ACTIVE: this status bit indicates whether or not a watchdog timer device
>> - is active or not. When the watchdog is active after booting, then you should
>> - set this status bit (Note: when you register the watchdog timer device with
>> - this bit set, then opening /dev/watchdog will skip the start operation)
>> + is active or not from user perspective. User space is expected to send
>> + heartbeat requests to the driver while this flag is set. If the watchdog
>> + is active after booting, and you don't want the infrastructure to send
>> + heartbeats to the watchdog driver, then you should set this status bit.
>
> IMHO this should not be the driver author's choice! If you implement
> policy in the kernel it should at least be implemented in the framework
> and preferably easily changeable. (At least with Kconfig, but better use
> a kernel parameter (or both, the latter overriding the former).)
>
Agreed. I'll change that and simply drop that part. After all,
we now have WDOG_RUNNING to indicate that the watchdog is running.
I'll just have to make sure that there are no drivers which set
WDOG_ACTIVE at boot (afaics there are none).

>> + Note: when you register the watchdog timer device with this bit set,
>> + then opening /dev/watchdog will skip the start operation.
>> * WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
>> was opened via /dev/watchdog.
>> (This bit should only be used by the WatchDog Timer Driver Core).
>> @@ -209,6 +213,11 @@ bit-operations. The status bits that are defined are:
>> any watchdog_ops, so that you can be sure that no operations (other then
>> unref) will get called after unregister, even if userspace still holds a
>> reference to /dev/watchdog
>> +* WDOG_RUNNING: Set by the watchdog driver if the hardware watchdog is running.
>> + The bit must be set if the watchdog timer hardware can not be stopped.
>> + The bit may also be set if the watchdog timer is running aftyer booting,
>> + before the watchdog device is opened. If set, the watchdog infrastructure
>> + will send keepalives to the watchdog hardware while WDOG_ACTIVE is not set.
>>
>> To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
>> timer device) you can either:
>> [...]
>> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
>> index c04ba1a98cc8..676e233d5e7b 100644
>> --- a/drivers/watchdog/watchdog_dev.c
>> +++ b/drivers/watchdog/watchdog_dev.c
>> @@ -59,7 +59,8 @@ static inline bool watchdog_need_worker(struct watchdog_device *wdd)
>> unsigned int m = wdd->max_timeout * 1000;
>> unsigned int t = wdd->timeout * 1000;
>>
>> - return watchdog_active(wdd) && hm && (!m || hm < m) && t > hm;
>> + return (watchdog_active(wdd) && hm && (!m || hm < m) && t > hm) ||
>> + (t && !watchdog_active(wdd) && watchdog_running(wdd));
>
> What is the meaning of
>
> !t && !watchdog_active(wdd) && watchdog_running(wdd)
>
> ? Can this happen at all? If not, drop "t && "?
>
t can be 0, meaning "the watchdog timeout is unknown", unless a driver sets min_timeout
to a value larger than 0. Unfortunately, that is not explicitly specified.

Thanks,
Guenter