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 69990C636D4 for ; Tue, 7 Feb 2023 21:20:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229935AbjBGVUB (ORCPT ); Tue, 7 Feb 2023 16:20:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58572 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229590AbjBGVT6 (ORCPT ); Tue, 7 Feb 2023 16:19:58 -0500 Received: from mail-ot1-f42.google.com (mail-ot1-f42.google.com [209.85.210.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CCD0817175; Tue, 7 Feb 2023 13:19:57 -0800 (PST) Received: by mail-ot1-f42.google.com with SMTP id 70-20020a9d084c000000b0068bccf754f1so4650008oty.7; Tue, 07 Feb 2023 13:19:57 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Z47pTYQ+/5OctvC8ddoYwu8QG4IsEwXm/DVEAF/PVtM=; b=SoyK9tJb5xYN3u/LN3HwBLhozTCRChlbn5319JwIwTUi55OTl0NIyBESxnHHWUfzDy QPd1fKY6PqK1wVSSo8pWsrEB/OoZqgEF2fc8iCZJfxDLNaY4BNVJqNvclXO2A2WE9QAI i0ECL8gX11a++cqDEWcegiz0LOESfj6ueWnK/SaUZFSwKWm03KfLmkhQCLrUvmXplKTT VFE3zBb/vTzxzrcHMZEUdlzSGYX1NXRZOksINSN40sjSvdNSO97gxIKLGimEnqcSv/Bt +dJyaLqL8wXg3qvXc+jNCxkmc7arTNR0WPml8/zQbZBuQkmOk/InS4o46dmOYAQgRaDw hFuw== X-Gm-Message-State: AO0yUKWr84srnArgXSiDpQb7Z2aZaEEouuElxY8DY8glx5C6v/aNL3He zDpGm+ooMq/PCa4FM4au9in+qENHNw== X-Google-Smtp-Source: AK7set/diBRHF4lI5GQLqN0GdFX+iy7l2cjOo76iYc6ZAnC18tkVaZyWtWStK7hjiJcpjbgQkX/zug== X-Received: by 2002:a9d:177:0:b0:68d:a785:5f5f with SMTP id 110-20020a9d0177000000b0068da7855f5fmr2872911otu.2.1675804796999; Tue, 07 Feb 2023 13:19:56 -0800 (PST) Received: from robh_at_kernel.org (66-90-144-107.dyn.grandenetworks.net. [66.90.144.107]) by smtp.gmail.com with ESMTPSA id a24-20020a9d4718000000b0068d3f341dd9sm7019996otf.62.2023.02.07.13.19.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Feb 2023 13:19:56 -0800 (PST) Received: (nullmailer pid 4171931 invoked by uid 1000); Tue, 07 Feb 2023 21:19:55 -0000 Date: Tue, 7 Feb 2023 15:19:55 -0600 From: Rob Herring To: Douglas Anderson Cc: Krzysztof Kozlowski , linux-input@vger.kernel.org, Stephen Kitt , Bjorn Andersson , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, Dmitry Torokhov , Benjamin Tissoires , devicetree@vger.kernel.org, Konrad Dybcio , Rob Herring , Jiri Kosina Subject: Re: [PATCH 5/7] dt-bindings: HID: i2c-hid: goodix: Add mainboard-vddio-supply Message-ID: <167580479546.4171868.14123127361187653098.robh@kernel.org> References: <20230207024816.525938-1-dianders@chromium.org> <20230206184744.5.Ia77a96c6c5564f9cc25e6220b5a9171d5c2639e8@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230206184744.5.Ia77a96c6c5564f9cc25e6220b5a9171d5c2639e8@changeid> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 06 Feb 2023 18:48:14 -0800, Douglas Anderson wrote: > The goodix i2c-hid bindings currently support two models of > touchscreen: GT7375P and GT7986U. The datasheets of both touchscreens > show the following things: > * The mainboard that the touchscreen is connected to is only expected > to supply one voltage to the touchscreen: 3.3V. > * The touchscreen, depending on stuffing options, can accept IO to the > touchscreen as either 3.3V or 1.8V. Presumably this means that the > touchscreen has its own way internally to make or deal with 1.8V > signals when it's configured for 1.8V IO. > > NOTE: you've got to look very carefully at the datasheet for the > touchscreen to see that the above bullets are true. Specifically, the > datasheet shows a signal called VDDIO and one might think that this is > where a mainboard would provide VDDIO to the touchscreen. Upon closer > inspection, however, a footnote can be found that says "When VDDIO is > left floating, the logic level is 1.8V [...]; when VDDIO is connected > to AVDD, the logic level is AVDD.". Thus the VDDIO pin on the > touchscreen IC is actually a selector and not a pin whre the mainboard > would pass a reference voltage. > > The fact that the touchscreen isn't supplied 1.8V by the mainboard > means that when I originally submitted bindings for these touchscreens > I only listed the 3.3V rail in the bindings. It can be noted that the > original bindings and driver were added for sc7180-trogdor boards and > these boards all use 3.3V IO via a level shifter on the mainboard. > > It turns out that with sc7280-herobrine-evoker, we've got a bit of a > strange monkey on our hands. Due to some very interesting but > (unfortunately) set-in-stone hardware design, we are doing 1.8V IO to > the touchscreen but we _also_ have some extra buffers on the mainboard > that need to be powered up to make the IO lines work. After much > pondering about this, it seems like the best way to handle this is to > add an optional "mainboard-vddio" rail to the bindings that is used to > power up the buffers. Specifically, the fact that the touchscreen > datasheet documents that its IOs can be at a different voltage level > than its main power rail means that there truly are two voltage rails > associated with the touchscreen, even if we don't actually provide the > IO rail to it. Thus it doesn't feel absurd for the DT node on the host > to have a 1.8V rail to power up anything related to its 1.8V logic. > > Signed-off-by: Douglas Anderson > --- > > .../devicetree/bindings/input/goodix,gt7375p.yaml | 7 +++++++ > 1 file changed, 7 insertions(+) > Acked-by: Rob Herring