linux-kernel - Fwd: watchdog: WatchDog Timer Driver Core: ping a hardware watchdog in kernel's space [proposal]

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Date:	Fri, 05 Sep 2014 08:47:28 +0200
From:	Janusz Użycki <j.uzycki@...roma.com.pl>
To:	linux-kernel@...r.kernel.org
Subject: Fwd: watchdog: WatchDog Timer Driver Core: ping a hardware watchdog
 in kernel's space [proposal]

Hi,

Some applications require to start watchdog before userspace software.
This patch enables such feature. Only WATCHDOG_KERNEL_PING flag is necessary to enable it (attached example for stmp3xxx_rtc_wdt.c).
Moreover kernel's ping is re-enabled when userspace software closed watchdog using the magic character.
The features improves kernel's reliable if hardware watchdog is available.

* Can you comment the proposed patch?
* Shoud dynamic or static timer_list be used (small structure...)?
* I also added wdd->ops->ref/unref calls but I'm afraid that even original code is buggy in watchdog_dev.c.
Is any driver that uses the pointers?
In my opinion watchdog_open() should call wdd->ops->ref() before watchdog_start() and watchdog_release() should call wdd->ops->unref() before module_put().
Otherwise fault is possible if watchdog module is unloaded.
* I noticed that current watchdog core does not support suspend/resume case.
If you want to use suspend without the patch you need to close a watchdog in userspace using the magic character before suspend command.
With the patch you must to use WDIOC_SETOPTIONS ioctl and WDIOS_DISABLECARD/WDIOS_ENABLECARD.
Is there any other method to suspend with watchdog?

best regards
Janusz Uzycki

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