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 29A5EC4332F for ; Fri, 16 Dec 2022 12:59:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229981AbiLPM72 (ORCPT ); Fri, 16 Dec 2022 07:59:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229928AbiLPM71 (ORCPT ); Fri, 16 Dec 2022 07:59:27 -0500 X-Greylist: delayed 493 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Fri, 16 Dec 2022 04:59:25 PST Received: from smtp-out-06.comm2000.it (smtp-out-06.comm2000.it [212.97.32.74]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9535D5214F for ; Fri, 16 Dec 2022 04:59:25 -0800 (PST) Received: from francesco-nb.int.toradex.com (93-49-2-63.ip317.fastwebnet.it [93.49.2.63]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: francesco@dolcini.it) by smtp-out-06.comm2000.it (Postfix) with ESMTPSA id B78DA563C24; Fri, 16 Dec 2022 13:51:07 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mailserver.it; s=mailsrv; t=1671195070; bh=EfBeTvttVoc82tq3ofLmEzobpG7NJbK0UtZUph4ruAE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=slrkRNWklL0vICs1jQcJiwtip3TE7VTBsQUcWNmbWgp9uPfjrZwyhnMq4lPyNby+7 K7nrs1BzC4oyfd9/Jqzt57pYjC20u/Mt/1YJ0Bx/hRhW12ly8vW0LDq5uVDOuq3EfY g1+vRepyJxsD1BFdOysWWHIBa6YfrkabclDjrRJb+RlbKAU9cUA10MySzRC24pKT9w gmAMoNbZFfSsIrD9Y23+eRAlpKhmPmRWZgDltbho7p0F8q8NLpS100DmRdrKQg0LWg ZWd1mXhM7Tfis3eTIwegOViRcO1kZU2ooAW2jKXhCTM6HK1iYViw8NEA+o8gKV5zUA R9ebkEltPzUUQ== Date: Fri, 16 Dec 2022 13:51:03 +0100 From: Francesco Dolcini To: Primoz Fiser Cc: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Oleksij Rempel , linux-kernel@vger.kernel.org, Shawn Guo , Sascha Hauer , upstream@lists.phytec.de, Marco Felsch , Oleksij Rempel , NXP Linux Team , Pengutronix Kernel Team , Fabio Estevam , linux-arm-kernel@lists.infradead.org, linux-i2c@vger.kernel.org, francesco.dolcini@toradex.com Subject: Re: [PATCH] i2c: imx: increase retries on arbitration loss Message-ID: References: <20221216084511.2576786-1-primoz.fiser@norik.com> <20221216094518.bevkg5buzu7iybfh@pengutronix.de> <20221216110227.GA12327@pengutronix.de> <20221216111308.wckibotr5d3q6ree@pengutronix.de> <5c2e0531-e7c3-1b37-35ed-c8e9795a0d18@norik.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5c2e0531-e7c3-1b37-35ed-c8e9795a0d18@norik.com> Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On Fri, Dec 16, 2022 at 01:23:29PM +0100, Primoz Fiser wrote: > Hi all, > > On 16. 12. 22 12:13, Uwe Kleine-König wrote: > > On Fri, Dec 16, 2022 at 12:02:27PM +0100, Oleksij Rempel wrote: > > > On Fri, Dec 16, 2022 at 11:41:08AM +0100, Primoz Fiser wrote: > > > > Hi Marco, > > > > > > > > On 16. 12. 22 10:45, Marco Felsch wrote: > > > > > Hi Primoz, > > > > > > > > > > On 22-12-16, Primoz Fiser wrote: > > > > > > By default, retries value is set to 0 (no retries). Set retries to more > > > > > > sensible value of 3 to allow i2c core to re-attempt transfer in case of > > > > > > i2c arbitration loss (i2c-imx returns -EAGAIN errno is such case). > > > > > > > > > > apart the fact that the number of retries vary a lot and so the client > > > > > driver behaviour can vary a lot which is not good IMHO, why do you think > > > > > that 3 is a sufficient number? > > > > > > > > IMHO it is better than leaving it at 0 (no retries)? > > > > > > > > Setting it to sensible value like 3 will at least attempt to make transfer > > > > in case arbitration-loss occurs. > > > > > > > > > > > > > > If an arbitration loss happen, why do you think that retrying it 3 times > > > > > changes that? > > > > > > > > I our case, setting retries to non-zero value solves issues with PMIC > > > > shutdown on phyboard-mira which in some rare cases fails with "Failed to > > > > shutdown (err = -11)" (-EAGAIN). > > > > > > > > To me it makes common sense retries is set to non-zero value especially for > > > > such rare conditions/situations. > > > > > > https://lore.kernel.org/all/Ys1bw9zuIwWS+bqw@shikoro/ > > Ohh I see. > > Reading through the thread I guess we aren't getting this mainlined at all > :) > > The only solid point in the thread seems to be that in that case we are not > covering up the potential i2c hardware issues? I believe that in this case we should just have a warning in the kernel. The retry potentially work-around a transient issue and we do not hide any hardware issue at the same time. It seems an easy win-win solution. > Yeah fair point but on the other hand, goal of this patch would be to > improve robustness in case of otherwise good performing hardware. From user > perspective I just want it to work despite it retrying under the hood from > time to time. I think Francesco had the same idea. Unfortunately I was missing the exact background that made us do this change, we just had it sitting in our fork for too long :-/ This is one of the reason I gave up on it. Quoting Uwe [1] > sometimes there is no practical way around such work arounds. I happens > from time to time that the reason for problem is known, but fixing the > hardware is no option, then you need such workrounds. (This applies to > both, retrying the transfers and resetting the bus.) Francesco [1] https://lore.kernel.org/all/20220715083400.q226rrwxsgt4eomp@pengutronix.de/