From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756186AbbBCTCO (ORCPT ); Tue, 3 Feb 2015 14:02:14 -0500 Received: from spo001.leaseweb.nl ([83.149.101.17]:59186 "EHLO spo001.leaseweb.nl" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S966294AbbBCTCL (ORCPT ); Tue, 3 Feb 2015 14:02:11 -0500 Date: Tue, 3 Feb 2015 20:01:53 +0100 From: Wim Van Sebroeck To: Doug Anderson Cc: Guenter Roeck , Heiko Stuebner , Lunxue Dai , Jisheng Zhang , Dinh Nguyen , linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] watchdog: dw_wdt: pat the watchdog before enabling it Message-ID: <20150203190153.GD2875@spo001.leaseweb.nl> References: <1422397517-20426-1-git-send-email-dianders@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1422397517-20426-1-git-send-email-dianders@chromium.org> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Doug, > 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 Patch has been added to linux-watchdog-next. Kind regards, Wim.