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From: Guenter Roeck <linux@roeck-us.net>
To: Doug Anderson <dianders@chromium.org>, Wim Van Sebroeck <wim@iguana.be>
Cc: Heiko Stuebner <heiko@sntech.de>,
	Lunxue Dai <lunxue.dai@rock-chips.com>,
	Jisheng Zhang <jszhang@marvell.com>,
	Dinh Nguyen <dinguyen@altera.com>,
	linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] watchdog: dw_wdt: pat the watchdog before enabling it
Date: Mon, 26 Jan 2015 18:12:25 -0800	[thread overview]
Message-ID: <54C6F409.2030206@roeck-us.net> (raw)
In-Reply-To: <1422314836-30516-1-git-send-email-dianders@chromium.org>

On 01/26/2015 03:27 PM, 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_mmc 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@chromium.org>

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


  parent reply	other threads:[~2015-01-27  2:12 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-26 23:27 Doug Anderson
2015-01-26 23:27 ` [PATCH v2 2/2] watchdog: dw_wdt: Try to get a 30 second watchdog by default Doug Anderson
2015-01-27  2:12 ` Guenter Roeck [this message]
2015-01-27  3:49 ` [PATCH v2 1/2] watchdog: dw_wdt: pat the watchdog before enabling it Jisheng Zhang
2015-01-27  4:08   ` Guenter Roeck
2015-01-27  4:52     ` Jisheng Zhang

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