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

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Date:	Thu, 5 Nov 2015 08:08:55 -0600
From:	Timur Tabi <timur@...eaurora.org>
To:	Fu Wei <fu.wei@...aro.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

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

-- 
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.
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