linux-kernel - Re: [PATCH v3 1/2] watchdog: dw_wdt: pat the watchdog before enabling it

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Date:	Wed, 28 Jan 2015 10:58:43 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Wim Van Sebroeck <wim@...ana.be>, Heiko Stuebner <heiko@...ech.de>,
	Lunxue Dai <lunxue.dai@...k-chips.com>,
	Jisheng Zhang <jszhang@...vell.com>,
	Dinh Nguyen <dinguyen@...era.com>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] watchdog: dw_wdt: pat the watchdog before
 enabling it

On Tue, Jan 27, 2015 at 02:25:16PM -0800, Doug Anderson wrote:
> On some dw_wdt implementations the "top" register may be initted to 0
> at bootup.  In such a case, each "pat" of the watchdog will reset the
> timer to 0xffff.  That's pretty short.
> 
> The input clock of the wdt can be any of a wide range of values.  On
> an rk3288 system, I've seen the wdt clock be 24.75 MHz.  That means
> each tick is ~40ns and we'll count to 0xffff in ~2.6ms.
> 
> Because of the above two facts, it's a really good idea to pat the
> watchdog after initting the "top" register properly and before
> enabling the watchdog.  If you don't then there's no way we'll get the
> next heartbeat in time.
> 
> Jisheng Zhang fixed this problem on some dw_wdt versions by using the
> TOP_INIT feature.  However, the dw_wdt on rk3288 doesn't have TOP_INIT
> so it's a good idea to also pat the watchdog manually.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>
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