linux-kernel - Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

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Message-ID: <5577180E.4070804@roeck-us.net>
Date:	Tue, 09 Jun 2015 09:45:02 -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>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>, rjw@...ysocki.net
Subject: Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

On 06/09/2015 09:29 AM, Timur Tabi wrote:
> On 06/09/2015 11:22 AM, Guenter Roeck wrote:
>>
>>
>> but I see your point. Essentially, the specification is broken
>> for all practical purposes, since, as you point out, enabling
>> the watchdog overwrites and explicitly sets WCV. Effectively
>> this means that just using WCV to program the timeout period
>> is not really possible.
>>
>> I am not really sure how to address this. We can either only use WOR,
>> and forget about pretimeout, or we can enforce a minimum pretimeout.
>> In the latter case, we'll have to write WCV after writing WOR.
>
> In talking with our hardware engineers, using WCV to program the timeout period is not a valid operation.  This is why I keep arguing against the pre-timeout feature, and I don't agree that servers should always use pre-timeout.
>

Not sure if "not valid" is correct - after all, it is mentioned in the
specification. However, it is at the very least fragile.

I tend to agree that we should just forget about pretimeout and
use your original approach, where the timeout value is used
to program WOR. Everything else is really just asking for trouble.

Guenter

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