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

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Date:	Mon, 25 May 2015 01:04:35 +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 00:58, Guenter Roeck <linux@...ck-us.net> wrote:
> On 05/24/2015 09:47 AM, Fu Wei wrote:
>>
>> Hi Guenter,
>>
>> On 25 May 2015 at 00:23, Guenter Roeck <linux@...ck-us.net> wrote:
>>>
>>> On 05/24/2015 08:50 AM, Fu Wei wrote:
>>> [ ...]
>>>
>>>> Actually, I have added my thought at the head of sbsa_gwdt.c as a
>>>> comment
>>>> :
>>>>
>>>>     *
>>>>    * Note: This SBSA Generic watchdog driver is compatible with
>>>>    *       the pretimeout concept of Linux kernel.
>>>>    *       The timeout and pretimeout are set by the different REGs.
>>>>    *       The first watch period is set by writing WCV directly,
>>>>    *       that can support more than 10s timeout at the maximum
>>>>    *       system counter frequency.
>>>>    *       The second watch period is set by WOR(32bit) which will be
>>>> loaded
>>>>    *       automatically by hardware, when WS0 is triggered.
>>>>    *       This gives a maximum watch period of around 10s at the
>>>> maximum
>>>>    *       system counter frequency.
>>>>    *       The System Counter shall run at maximum of 400MHz.
>>>>    *       More details: DEN0029B - Server Base System Architecture
>>>> (SBSA)
>>>>    *
>>>>    * Kernel/API:                         P---------| pretimeout
>>>>    *               |-------------------------------T timeout
>>>>    * SBSA GWDT:                          P--WOR---WS1 pretimeout
>>>>    *               |-------WCV----------WS0~~~~~~~~T timeout
>>>>    */
>>>>
>>>
>>> Yes, but do we actually _know_ that it works that way, ie that WCV
>>> drives WS0 and that WOR drives WS1 ? Unless I am missing something,
>>> the specification doesn't say that, and it would have been a really
>>> easy statement to make if that was the intent.
>>
>>
>> yes, Suravee has tested it on Seattle B0 Soc, that works.
>> But hope Suravee can provide more info about test, I will ping him later.
>>
>> According to SBSA,  that WCV  and WOR can both drive WS1 and WS0
>>
>> the timeout and pretimeout in my patchset have been tested on Seattle
>> B0 and  Foundation model.
>>
>>>
>>> My concern here is that the above behavior is not spelled out in
>>> the document, meaning it is up to interpretation by the hardware
>>> engineer implementing it, to the point where it appears that not
>>> even two software engineers can agree how it is supposed to work.
>>> Which is a really bad starting point :-(.
>>
>>
>> Is that a real hardware teat can prove it works?
>>
>> or actually, SBSA say that it should work:
>> -----------------
>> Note: the watchdog offset register is 32 bits wide. This gives a
>> maximum watch period of around 10s at a system
>> counter frequency of 400MHz. If a larger watch period is required then
>> the compare value can be programmed
>> directly into the compare value register.
>> -----------------
>> offset register == WOR
>> compare value register == WCV
>>
>
> Where does it say that WCV shall be associated with WS0 and that WOR
> shall be associated with WS1 ? Guess I am missing that part.

no, it doesn't say WCV shall be associated with WS0, that is my driver doing.

but WCV can control both WS1/WS0.  WOR is just a auto-reload value.

I think maybe you can read SBSA 2.3 Page 23,  The  pseudocode can
explain everything. :-)

Great thanks for your time

>
>
> Thanks,
> Guenter
>
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-- 
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,
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