From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754271AbbAUXfy (ORCPT ); Wed, 21 Jan 2015 18:35:54 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:39669 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753255AbbAUXfo (ORCPT ); Wed, 21 Jan 2015 18:35:44 -0500 Message-ID: <54C037CC.2070707@roeck-us.net> Date: Wed, 21 Jan 2015 15:35:40 -0800 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Doug Anderson , Wim Van Sebroeck CC: Heiko Stuebner , Lunxue Dai , Jisheng Zhang , Dinh Nguyen , linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] watchdog: dw_wdt: pat the watchdog before enabling it References: <1421882243-3631-1-git-send-email-dianders@chromium.org> In-Reply-To: <1421882243-3631-1-git-send-email-dianders@chromium.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A020205.54C037CF.0095,ss=1,re=0.001,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.001 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 9 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/21/2015 03:17 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. > > Signed-off-by: Doug Anderson > --- Reviewed-by: Guenter Roeck