linux-kernel - Re: [Linaro-acpi] [PATCH v8 5/5] Watchdog: introduce ARM SBSA watchdog driver

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Date:	Thu, 5 Nov 2015 22:35:57 +0800
From:	Fu Wei <fu.wei@...aro.org>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>, Jon Masters <jcm@...hat.com>,
	Pratyush Anand <panand@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Catalin Marinas <catalin.marinas@....com>,
	Wei Fu <tekkamanninja@...il.com>,
	Rob Herring <robherring2@...il.com>,
	Vipul Gandhi <vgandhi@...eaurora.org>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [Linaro-acpi] [PATCH v8 5/5] Watchdog: introduce ARM SBSA
 watchdog driver

Hi Timur,

On 5 November 2015 at 22:08, Timur Tabi <timur@...eaurora.org> wrote:
> Fu Wei wrote:
>>
>> SBSA 2.3 Page 23 :
>> 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.
>>
>> 214s means your system counter is approximately at 20MHz which is in
>> the range of (10MHz ~ 400MHz)
>>
>> SBSA 2.3 Page 13 :
>> The System Counter (of the Generic Timer) shall run at a minimum
>> frequency of 10MHz and maximum of
>> 400MHz.
>
>
> Thanks, that explains a lot.
>
> If we expected customers to have a lower system counter frequency, then we
> wouldn't have to worry about the timeouts being too short.  It seems to me
> that the SBSA spec says that if you want a longer timeout, you have to lower
> the frequency.

Did you really read the "Note" above???????? OK, let me paste it again
and again:

SBSA 2.3 Page 23 :
If a larger watch period is required then the compare value can be
programmed directly into the compare value register.

> We shouldn't be complicating the driver because some
> customers might not follow the spec.

OK it this customer might not follow the spec, that watchdog is not a
SBSA watchdog,
So please don't use SBSA watchdog driver on that non-SBSA watchdog
device, Thanks a lot

>
>
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the
> Code Aurora Forum, hosted by The Linux Foundation.



-- 
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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