linux-kernel - Re: [PATCH v2 6/7] Watchdog: introduce ARM SBSA watchdog driver

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Date:	Sun, 24 May 2015 09:29:36 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Timur Tabi <timur@...eaurora.org>, Fu Wei <fu.wei@...aro.org>
CC:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Wei Fu <tekkamanninja@...il.com>,
	G Gregory <graeme.gregory@...aro.org>,
	Al Stone <al.stone@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, vgandhi@...eaurora.org,
	wim@...ana.be, Jon Masters <jcm@...hat.com>,
	Leo Duran <leo.duran@....com>, Jon Corbet <corbet@....net>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 6/7] Watchdog: introduce ARM SBSA watchdog driver

On 05/24/2015 09:13 AM, Timur Tabi wrote:
> Fu Wei wrote:
>> in the first timeout, just panic()  maybe not enough,  in [RFC]
>> version of my patchset, I offer some option as "preaction" to use, but
>> for simplifying the first version of driver, I have deleted them.
>> but at least, panic() is far more useful than a simple reset.  at
>> least, it can provide the context of the crashed system  to admin.
>
> My point is that there is very little difference between
>
> 1) calling panic() on pre-timeout
> 2) calling panic() on timeout
>

The assumption would be that the second timeout doesn't cause a panic
but a system reset.

> In both cases, the system will panic.  The watchdog API says that the system should reset when a timeout occurs, so you cannot call panic() before the timeout expires.
>
>  > If you want to warn user space, that will make driver more
>  > complicated, I don't think that is a good choose for a first version.
>  > but we can find a way to improve this later
>
> In my opinion, this "first version" is not useful.  I would like to see a pre-timeout feature that does not panic or reset when a pre-timeout occurs.
>

The current watchdog API suggests that the pretimeout "allows Linux
to record useful information (like panic information and kernel
coredumps) before it resets". The call to panic() would be the
means to make this happen.

Are you suggesting to change this definition ? What should it do
instead in your opinion ?

Thanks,
Guenter

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