From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:44603 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751453AbbA0CMb (ORCPT ); Mon, 26 Jan 2015 21:12:31 -0500 Received: from mailnull by bh-25.webhostbox.net with sa-checked (Exim 4.82) (envelope-from ) id 1YFvdn-002iHV-T1 for linux-watchdog@vger.kernel.org; Tue, 27 Jan 2015 02:12:32 +0000 Message-ID: <54C6F409.2030206@roeck-us.net> Date: Mon, 26 Jan 2015 18:12:25 -0800 From: Guenter Roeck 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 v2 1/2] watchdog: dw_wdt: pat the watchdog before enabling it References: <1422314836-30516-1-git-send-email-dianders@chromium.org> In-Reply-To: <1422314836-30516-1-git-send-email-dianders@chromium.org> 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 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 Reviewed-by: Guenter Roeck