linux-kernel - Re: [PATCH RFC] Watchdog: sbsa

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Date:	Thu, 5 May 2016 16:51:14 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Timur Tabi <timur@...eaurora.org>,
	Pratyush Anand <panand@...hat.com>
Cc:	fu.wei@...aro.org, Suravee.Suthikulpanit@....com, wim@...ana.be,
	linux-arm-kernel@...ts.infradead.org,
	linux-watchdog@...r.kernel.org,
	open list <linux-kernel@...r.kernel.org>,
	Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org
Subject: Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range

On 05/05/2016 04:38 PM, Timur Tabi wrote:
> Guenter Roeck wrote:
>> A 32-bit counter is absolutely fine. Letting it run with a 400MHz clock
>> (or was it 200 MHz ?) is the problem. A resolution of 2.5ns for a watchdog
>> timer does not really make any sense.
>
> The 10 second limit is based on a 20MHz clock.
>
Not that a resolution of 50 ns makes sense either, but 4294967296 / 20971520 = 204,
and 20971520 * 10 = 209715200 = 0x0c800000. Where does the resolution get lost ?

Guenter