From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19A85C3814E for ; Tue, 23 Aug 2022 10:47:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355702AbiHWKr5 (ORCPT ); Tue, 23 Aug 2022 06:47:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355855AbiHWKo7 (ORCPT ); Tue, 23 Aug 2022 06:44:59 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD12574DD1 for ; Tue, 23 Aug 2022 02:10:49 -0700 (PDT) Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1oQPvZ-0005FD-CQ; Tue, 23 Aug 2022 11:10:29 +0200 Received: from mfe by ptx.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1oQPvX-0006WH-PG; Tue, 23 Aug 2022 11:10:27 +0200 Date: Tue, 23 Aug 2022 11:10:27 +0200 From: Marco Felsch To: "Alice Guo (OSS)" Cc: Guenter Roeck , "wim@linux-watchdog.org" , "shawnguo@kernel.org" , "s.hauer@pengutronix.de" , "festevam@gmail.com" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , dl-linux-imx , "kernel@pengutronix.de" , "linux-watchdog@vger.kernel.org" Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence Message-ID: <20220823091027.ezyxkn64asajvjom@pengutronix.de> References: <20220816043643.26569-1-alice.guo@oss.nxp.com> <20220816043643.26569-3-alice.guo@oss.nxp.com> <20220816062330.z2fvurteg337krw2@pengutronix.de> <20220822080010.ecdphpm3i26cco5f@pengutronix.de> <20220822140347.GA4087281@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: mfe@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-watchdog@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On 22-08-23, Alice Guo (OSS) wrote: > > > > -----Original Message----- > > From: Guenter Roeck On Behalf Of Guenter Roeck > > Sent: Monday, August 22, 2022 10:04 PM > > To: Marco Felsch > > Cc: Alice Guo (OSS) ; wim@linux-watchdog.org; > > shawnguo@kernel.org; s.hauer@pengutronix.de; festevam@gmail.com; > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; > > dl-linux-imx ; kernel@pengutronix.de; > > linux-watchdog@vger.kernel.org > > Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for > > unlock sequence > > > > On Mon, Aug 22, 2022 at 10:00:10AM +0200, Marco Felsch wrote: > > > On 22-08-22, Alice Guo (OSS) wrote: > > > > > -----Original Message----- > > > > > From: Marco Felsch > > > > > Sent: Tuesday, August 16, 2022 2:24 PM > > > > > To: Alice Guo (OSS) > > > > > Cc: wim@linux-watchdog.org; linux@roeck-us.net; > > > > > shawnguo@kernel.org; s.hauer@pengutronix.de; festevam@gmail.com; > > > > > linux-arm-kernel@lists.infradead.org; > > > > > linux-kernel@vger.kernel.org; dl-linux-imx ; > > > > > kernel@pengutronix.de; linux-watchdog@vger.kernel.org > > > > > Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory > > > > > barrier for unlock sequence > > > > > > > > > > On 22-08-16, Alice Guo (OSS) wrote: > > > > > > From: Jacky Bai > > > > > > > > > > > > Add explict memory barrier for the wdog unlock sequence. > > > > > > > > > > Did you inspected any failures? It's not enough to say what you > > > > > did, you need to specify the why as well. > > > > > > > > > > Regards, > > > > > Marco > > > > > > > > Hi, > > > > > > > > Two 16-bit writes of unlocking the Watchdog should be completed within a > > certain time. The first mb() is used to ensure that previous instructions are > > completed. > > > > The second mb() is used to ensure that the unlock sequence cannot be > > affected by subsequent instructions. The reason will be added in the commit > > log of v2. > > > > > > Hi, > > > > > > I know what memory barriers are. My question was, did you see any > > > issues? Since the driver is used mainline and no one reported issues. > > > > > > Also just don't use the *_relaxed() versions is more common, than > > > adding > > > mb() calls around *_relaxed() versions. > > > > > > > Agreed with both. The series is a bit short in explaining _why_ the changes are > > made. > > > > Guenter > > > > > Regards, > > > Marco > > > > > > > > > Hi Guenter and Marco, > > 1. did you see any issues? > This WDOG Timer first appeared in i.MX7ULP, no one report issues > probably because few people use i.MX7ULP. This issue was found when we > did a stress test on it. When we reconfigure the WDOG Timer, there is > a certain probability that it reset. The reason for the error is that > when WDOG_CS[CMD32EN] is 0, the unlock sequence is two 16-bit writes > (0xC520, 0xD928) to the CNT register within 16 bus clocks, and > improper unlock sequence causes the WDOG to reset. Adding mb() is to > guarantee that two 16-bit writes are finished within 16 bus clocks. After this explanation the whole imx7ulp_wdt_init() seems a bit buggy because writel_relaxed() as well as writel() are 32bit access functions. So the very first thing to do is to enable the 32-bit mode. Also this is a explanation worth to be added to the commit message ;) > 2. Also just don't use the *_relaxed() versions is more common, than > adding mb() calls around *_relaxed() versions. Memory barriers cannot > be added between two 16-bit writes. I do not know the reason. As written above, writel() as well as writel_relaxed() are not 16-bit access functions. So to me it looks as you need first to ensure that 32-bit access mode is enabled. After that you can write drop the to writel_relaxed() functions and instead just write: writel(UNLOCK, wdt->base + WDOG_CNT); Also why do we need to unlock the watchdog during imx7ulp_wdt_init()? This is handled just fine during imx7ulp_wdt_enable() and during imx7ulp_wdt_set_timeout(). So just drop those relaxed writes and everything should be fine. Regards, Marco