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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 572CDC43142 for ; Mon, 30 Jul 2018 23:24:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F4DA20881 for ; Mon, 30 Jul 2018 23:24:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F4DA20881 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731633AbeGaBCC (ORCPT ); Mon, 30 Jul 2018 21:02:02 -0400 Received: from mail-it0-f66.google.com ([209.85.214.66]:51486 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727094AbeGaBCC (ORCPT ); Mon, 30 Jul 2018 21:02:02 -0400 Received: by mail-it0-f66.google.com with SMTP id e14-v6so1754883itf.1; Mon, 30 Jul 2018 16:24:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=w3g/jaN+uEXeAyTQ3YZflKJHqL7zDsfnrXd5mT/1WmU=; b=EZSawt11LMAQwNaOWnbiueFrcJMZ8V1Koyax0gztGQ2mUaVFnQfsqw1nWIvaMzvrfM cd5/PC3FddLiK5txPMuEiJX9QW6UCW5FhcWrlaejRWWrNN3hIE+lRpZVYCaZGFBaTH9s rCUwXhMtWkt4IX48hDE8oHk7bQrlmIidYQT4P33bNVeGnyJ3zZAiq6g+FTJOrmN+aWNE Auaanat2VXtjwly+peHPb2yhv4oeWrh7qT395U3qjYFBlJYdEMDQDPt+vyZ/KdQslu2v anBVNyZ/0N7KPHnpXBovkA/yZdy4w+XB81OkanxzDGD0X82f4TxqVIU3sd1N7tjS2qI5 UQEA== X-Gm-Message-State: AOUpUlEIE2P27dtfxdrSoM7l+RrHsE7/xlznYHwI/ikadpEyM3gisED0 Mgh3Ci9TAJjnQX2Lxm0NMg== X-Google-Smtp-Source: AAOMgpfNFrlFilBCF2GJUj97pv0JgezviBpEes3MBTsa0lMzKDDJv9xBdQO2YDzZmHrQf1vzx+J21A== X-Received: by 2002:a24:54d:: with SMTP id 74-v6mr1082262itl.96.1532993082764; Mon, 30 Jul 2018 16:24:42 -0700 (PDT) Received: from localhost ([24.51.61.72]) by smtp.gmail.com with ESMTPSA id f3-v6sm3834774iok.29.2018.07.30.16.24.41 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 30 Jul 2018 16:24:41 -0700 (PDT) Date: Mon, 30 Jul 2018 17:24:41 -0600 From: Rob Herring To: Aapo Vienamo Cc: Stefan Agner , Ulf Hansson , Mark Rutland , Thierry Reding , Jonathan Hunter , Adrian Hunter , Mikko Perttunen , linux-mmc@vger.kernel.org, devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, linux-tegra-owner@vger.kernel.org Subject: Re: [PATCH v2 02/10] dt-bindings: mmc: tegra: Add nvidia,only-1-8-v property Message-ID: <20180730232441.GA17560@rob-hp-laptop> References: <1532607560-11253-1-git-send-email-avienamo@nvidia.com> <1532607560-11253-3-git-send-email-avienamo@nvidia.com> <484a31bdaad6d76b4fbb7d6fa80cbb8d@agner.ch> <20180727110555.1b7ad97d@dhcp-10-21-25-168> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180727110555.1b7ad97d@dhcp-10-21-25-168> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 27, 2018 at 11:05:55AM +0300, Aapo Vienamo wrote: > On Thu, 26 Jul 2018 15:05:55 +0200 > Stefan Agner wrote: > > > On 26.07.2018 14:19, Aapo Vienamo wrote: > > > Add a property to mark controllers which operate at a 1.8 V fixed I/O > > > voltage. > > > > > > This feature of the hardware needs to be signaled this way because it > > > cannot be probed at runtime or reliably derived from other properties. > > > > Is this really needed? Can we not use vqmmc to determine which voltage > > the controller runs on? > > > > There is already some precedence in the SDHCI core to determine which > > voltage levels are supported: > > https://lkml.org/lkml/2018/7/5/342 > > This property is introduced to solve a slightly different issue. The > thing is that supplying a fixed voltage SDHCI controller from a variable > regulator is still a valid configuration. Which means that testing the > capabilities of the regulator doesn't actually describe the SDHCI > controller itself. The regulator constraints should reflect this. The constraints aren't the capabilities of the regulator, but the limits on what it is supplying. > > In practice this property is used to communicate whether pad > reconfiguration and voltage switching needs to be performed or not. This > cannot be determined from the absence or presence of the pinctrl > properties either because they naturally won't be there on older dtbs. > > The logic behind this goes like this: if this property is present, > there's no need to perform pad or regulator reconfiguration and UHS > modes can be enabled. If this property is missing then valid pinctrl and > regulator properties are required to enable UHS signaling. This is > implemented in tegra_sdhci_is_uhs_valid() in "[PATCH v2 03/10] mmc: > tegra: Reconfigure pad voltages during voltage switching" > > -Aapo