linux-kernel - Re: [PATCH v10 5/5] Watchdog: ARM SBSA Generic Watchdog half timeout panic support

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Date:	Fri, 5 Feb 2016 15:54:37 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Fu Wei <fu.wei@...aro.org>
Cc:	Timur Tabi <timur@...eaurora.org>,
	Rob Herring <robh+dt@...nel.org>,
	Paweł Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Jon Corbet <corbet@....net>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-watchdog@...r.kernel.org, linux-doc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
	rruigrok@...eaurora.org, "Abdulhamid, Harb" <harba@...eaurora.org>,
	Christopher Covington <cov@...eaurora.org>,
	Dave Young <dyoung@...hat.com>,
	Pratyush Anand <panand@...hat.com>,
	G Gregory <graeme.gregory@...aro.org>,
	Al Stone <al.stone@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Jon Masters <jcm@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Leo Duran <leo.duran@....com>,
	Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v10 5/5] Watchdog: ARM SBSA Generic Watchdog half timeout
 panic support

On 02/05/2016 10:21 AM, Fu Wei wrote:
> On 5 February 2016 at 22:42, Guenter Roeck <linux@...ck-us.net> wrote:
>> On 02/05/2016 01:51 AM, Fu Wei wrote:
>>>
>>> Hi Guenter,
>>>
>>> On 4 February 2016 at 13:17, Guenter Roeck <linux@...ck-us.net> wrote:
>>>>
>>>> On 02/03/2016 03:00 PM, Fu Wei wrote:
>>>>>
>>>>>
>>>>> On 4 February 2016 at 02:45, Timur Tabi <timur@...eaurora.org> wrote:
>>>>>>
>>>>>>
>>>>>> Fu Wei wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> As you know I have made the pre-timeout support patch, If people like
>>>>>>> it, i am happy to go on upstream it separately.
>>>>>>>
>>>>>>> If we want to use pre-timeout here, user only can use get_pretimeout
>>>>>>> and disable panic by setting pretimeout to 0
>>>>>>> but user can not really set pretimeout, because "pre-timeout  ==
>>>>>>> timeout / 2 (always)".
>>>>>>> if user want to change pretimeout, he/she has to set_time instead.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Ok, I think patches 4 and 5 should be combined, and I think the Kconfig
>>>>>> entry should be removed and just use panic_enabled.
>>>>
>>>>
>>>>
>>>> Agreed.
>>>
>>>
>>> np, will do
>>>
>>>>>
>>>>>
>>>>> NP, will update this patchset like that ,  thanks :-)
>>>>>
>>>>
>>>> Also, if panic is enabled, the timeout needs to be adjusted accordingly
>>>> (to only panic after the entire timeout period has expired, not after
>>>> half of it). We can not panic the system after timeout / 2.
>>>
>>>
>>> OK, my thought is
>>>
>>> if panic is enabled :
>>> |--------WOR-------WS0--------WOR-------WS1
>>> |------timeout------(panic)------timeout-----reset
>>>
>>> if panic is disabled .
>>> |--------WOR-------WS0--------WOR-------WS1
>>> |---------------------timeout---------------------reset
>>>
>>>    panic_enabled only can be configured when module is loaded by module
>>> parameter
>>>
>>> But user should know that max_timeout(panic_enable) =
>>> max_timeout(panic_disable) / 2
>>>
>>
>> That means you'll have to update max_timeout accordingly.
>
> panic_enabled only can be configured when module is loaded, so we
> don't need to update it.
>
> max_timeout will only be set up in the init stage.
>
> Does it make sense ? :-)
>
Not sure I understand your problem or question.

max_timeout will have to reflect the correct maximum timeout, under
all circumstances. It will have to be set to the correct value before
the watchdog driver is registered.

Guenter