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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D8B3C433E1 for ; Mon, 3 Aug 2020 14:16:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59A93207DF for ; Mon, 3 Aug 2020 14:16:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="kSGrcoMk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728329AbgHCOQQ (ORCPT ); Mon, 3 Aug 2020 10:16:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726767AbgHCOQP (ORCPT ); Mon, 3 Aug 2020 10:16:15 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 779AAC06174A; Mon, 3 Aug 2020 07:16:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Qag0mgZqT4bNueVSCcbNmY9WCf2Ib/QmqRu677bcwIw=; b=kSGrcoMkWr8Ja1keSlEfp60kY P43VpVbqh45axG9v5UoRiB5LBDyE5T/C6vl4QTFD4c6VO8vx754cBGznLHIdd1GCKslyRoDjlVlJt SlL/bGYkLIUXgJ44wYaTtn6EpEBwX9LOFXAifa3WsLsz1AAoQzmmNE88amEF80+feG+lTI6hQJiNl /maSAJgNfJx2VOG9GdjVA0h4aMpbgwyT4QAm94N0KbjcFUZKd9JQ/IaK38Ti3BAbz5JkKEeJRkTU1 hjqNENuCeQEzZ4hYkPrV4/5dTp9Cg0QZcmo1TP7Abxypn66Vtj5dnQ23GmjgmgSLxTh06581vA4Kz wy0UaH4WA==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:47822) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1k2bGA-0001as-42; Mon, 03 Aug 2020 15:16:14 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1k2bG9-00039O-M1; Mon, 03 Aug 2020 15:16:13 +0100 Date: Mon, 3 Aug 2020 15:16:13 +0100 From: Russell King - ARM Linux admin To: Codrin.Ciubotariu@microchip.com Cc: wsa@kernel.org, linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, robh+dt@kernel.org, Ludovic.Desroches@microchip.com, Nicolas.Ferre@microchip.com, alexandre.belloni@bootlin.com, kamel.bouhara@bootlin.com Subject: Re: [RFC PATCH 1/4] dt-binding: i2c: add generic properties for GPIO bus recovery Message-ID: <20200803141613.GN1551@shell.armlinux.org.uk> References: <20200619141904.910889-1-codrin.ciubotariu@microchip.com> <20200619141904.910889-2-codrin.ciubotariu@microchip.com> <20200705211918.GB1055@kunai> <20200724193913.GD1227@ninjato> <20200724205209.GC1551@shell.armlinux.org.uk> <20200727105029.GI1551@shell.armlinux.org.uk> <1e788319-c841-d1f1-b65c-d25052f7f90b@microchip.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1e788319-c841-d1f1-b65c-d25052f7f90b@microchip.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 30, 2020 at 09:00:36AM +0000, Codrin.Ciubotariu@microchip.com wrote: > On 27.07.2020 13:50, Russell King - ARM Linux admin wrote: > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > > > On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote: > >> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: > >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > >>> > >>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: > >>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: > >>>>> > >>>>>> +- pinctrl > >>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > >>>>>> + recovery, call it "gpio" or "recovery" state > >>>>> > >>>>> I think we should stick with "gpio" only. That is what at91 and imx have > >>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I > >>>>> can't find any further use or documentation of that. PXA is not fully > >>>>> converted to the best of my knowledge, so maybe it is no problem for PXA > >>>>> to switch to "gpio", too? We should ask Russell King (cced). > >>> > >>> Fully converted to what? The generic handling where the i2c core layer > >>> handles everything to do with recovery, including the switch between > >>> modes? > >>> > >>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and > >>> GPIO mode, and I don't see a generic driver doing that to avoid causing > >>> any additional glitches on the bus. Given the use case that this recovery > >>> is targetted at, avoiding glitches is very important to keep. > >> > >> Why is it not possbile to handle glitches in a generic way? I guess it > >> depends on the pinctl, but we could treat a worst-case scenario to > >> assure the switch between states is done properly. > > > > Please look at how i2c-pxa switches between the two, and decide whether > > the generic implementation can do the same. > > The handling of glitches from initialization looks generic to me. I see > that there are specific clear/reset routines that are in the > (un)prepare_recovery() callbacks, but these callbacks are not replaced > by the generic i2c recovery and will still be used if given by the > driver. The only thing the generic recovery does is to switch the pinmux > state. We can discuss whether we want to change the pinmux state first > or call the (un)preapre_recovery(). Right, the key point i2c-pxa does is that on prepare: - read the current state of the SCL and SDA lines and set the GPIO to reflect those values. - then switch the pinmux state. That must be preserved, otherwise if SCL is being held low by the I2C master, and we switch to GPIO mode, SCL will be released. So the driver needs to be involved before the pinmux state is changed. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!