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=-0.6 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID 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 40853C43382 for ; Tue, 25 Sep 2018 15:23:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE70D20843 for ; Tue, 25 Sep 2018 15:23:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=lechnology.com header.i=@lechnology.com header.b="Br7xbS7b" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EE70D20843 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lechnology.com 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 S1729990AbeIYVbp (ORCPT ); Tue, 25 Sep 2018 17:31:45 -0400 Received: from vern.gendns.com ([206.190.152.46]:56701 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729332AbeIYVbo (ORCPT ); Tue, 25 Sep 2018 17:31:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lechnology.com; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To: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=eTmfUEFM9DLXqCHPgb3FfQfk5JbxPLJIiVCQyeNOtn0=; b=Br7xbS7bESFdLRN34dgFCErB6d 7fStRmDkStw4cKw4xfCI8klPenuBwZTEJdAvpVTS1os2eOlrbAhoGrC6AVyYPOU45iN9q27Bk2omn JREU9vu16kj65cZQLmzg4rNu5tNRaqHWn85unH7dkhDWcqQaWBDiin7au3qAX4//o7mKsMjgCC3PT jktvC+uR/IZDsGtzRWuI/ockjk/My3q2imbfW/rbrqhwSTOFCuhdJFJQ8eqHLcYdOnr28160o6TW9 3RQfnkfT3zP9n1EEB7xmKDQcxgW3UoSWIH0gsLbVrbmqLso+ILRPD6PmQUE4bFsMQ/8rUl6oogqfQ Yt64aIzQ==; Received: from 108-198-5-147.lightspeed.okcbok.sbcglobal.net ([108.198.5.147]:59380 helo=gerda.lechnology.com) by vern.gendns.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.91) (envelope-from ) id 1g4pBf-005Q3Q-Qu; Tue, 25 Sep 2018 11:23:43 -0400 Subject: Re: [PATCH] ARM: dts: da850-lego-ev3: slow down A/DC as much as possible To: Sekhar Nori Cc: Kevin Hilman , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180924013146.18121-1-david@lechnology.com> From: David Lechner Message-ID: Date: Tue, 25 Sep 2018 10:23:40 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/25/18 1:04 AM, Sekhar Nori wrote: > Hi David, > > On Monday 24 September 2018 07:01 AM, David Lechner wrote: >> Due to the electrical design of the A/DC circuits on LEGO MINDSTORMS EV3, >> if we are reading analog values as fast as possible (i.e. using DMA to >> service the SPI) the A/DC chip will read incorrect values - as much as >> 0.1V off when the SPI is running at 10MHz. (This has to do with the >> capacitor charge time when channels are muxed in the A/DC.) > > So you believe this is an issue with the board design rather than the > limitation of the ADC chip itself? Because if its the later, the fix > should be in the driver instead. It is the board design. There are external 4.7k series resistors that make the RC charge time so long. > >> >> Both of these patches mentioned have been picked up in the respective >> subsystems. > > Is this needed for the -rc cycle or can wait for v4.20? v4.20