From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:57508 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753388AbbA0EIJ (ORCPT ); Mon, 26 Jan 2015 23:08:09 -0500 Received: from mailnull by bh-25.webhostbox.net with sa-checked (Exim 4.82) (envelope-from ) id 1YFxRh-003r1I-RV for linux-watchdog@vger.kernel.org; Tue, 27 Jan 2015 04:08:10 +0000 Message-ID: <54C70F24.5080100@roeck-us.net> Date: Mon, 26 Jan 2015 20:08:04 -0800 From: Guenter Roeck MIME-Version: 1.0 To: Jisheng Zhang , Doug Anderson CC: Wim Van Sebroeck , Heiko Stuebner , Lunxue Dai , Dinh Nguyen , "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 References: <1422314836-30516-1-git-send-email-dianders@chromium.org> <20150127114909.204eeee0@xhacker> In-Reply-To: <20150127114909.204eeee0@xhacker> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-watchdog-owner@vger.kernel.org List-Id: linux-watchdog@vger.kernel.org On 01/26/2015 07:49 PM, Jisheng Zhang wrote: > Dear Doug, > > On Mon, 26 Jan 2015 15:27:15 -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_mmc versions by using the > > s/dw_mmc/dw_wdt > >> 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. > > Based on your register dumping, I see the following configurations on rk3288: > > WDT_DUAL_TOP is configured as false, so there's no TOP_INIT > > WDT_DFLT_TOP is configured as 0, so it will timeout soon. > > > So an extra pat is a must on such platforms with similar configurations. And it > doesn't hurt anything if we have an extra pat before enabling the WDT > > All in all, except the "dw_mmc" typo above, the patch looks good to me. > Jisheng, it would be great if you can provide configuration information shown in the (undocumented) registers. Doug, can you send another version with this information added as comment to the code ? This will help others to understand what is going on (and why) later on. Thanks, Guenter