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

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Date:	Mon, 25 May 2015 00:33:10 +0800
From:	Fu Wei <fu.wei@...aro.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Timur Tabi <timur@...eaurora.org>,
	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

Hi Guenter

On 25 May 2015 at 00:29, Guenter Roeck <linux@...ck-us.net> wrote:
> 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.

Yes, that is what I mean. Great thanks for your explanation. :-)

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



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
Ph: +86 21 61221326(direct)
Ph: +86 186 2020 4684 (mobile)
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021
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