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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 C6B65C432C3 for ; Fri, 22 Nov 2019 03:24:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BE64206C2 for ; Fri, 22 Nov 2019 03:24:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574393065; bh=iE3p1SKLOct5dnrnmKl/6ltpI6ePV5jd0Jn24rApQo4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=0Omlv7CETIogA5A+MM3f/XN/dyJBvOKwENMxhcdAMn5aicioUJx6K5nOHOwDsr43j uL/NJLNai3GWJmQKzW4SjzG4kvkdz5yV5ethLjYb9eUQ9W9jQAqB51gptZkfepmhQ9 pP/93APDFtTHyl3iyvcmrff9pU4nCY801xYebF/A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726613AbfKVDYY (ORCPT ); Thu, 21 Nov 2019 22:24:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:34476 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726335AbfKVDYY (ORCPT ); Thu, 21 Nov 2019 22:24:24 -0500 Received: from localhost (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4F08E2067D; Fri, 22 Nov 2019 03:24:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574393063; bh=iE3p1SKLOct5dnrnmKl/6ltpI6ePV5jd0Jn24rApQo4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J0QsnJoRDUmg0O+Hq5suKVJNR0x7BaZjihZz2MgesejyZHnAiKNjICKnPQj1uxdcK iqB9QNXZn802hSg58ech4sMOptU/83arMJjRqAYGNdr/XBQXxT5qzouZVZ4Gp4GhG9 0waNU23Nm/zB3BSjFprpl67wN8HmcfEf1gZBT0O0= Date: Thu, 21 Nov 2019 22:24:22 -0500 From: Sasha Levin To: David Lechner Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Sekhar Nori , devicetree@vger.kernel.org Subject: Re: [PATCH AUTOSEL 4.19 087/209] ARM: dts: da850-lego-ev3: slow down A/DC as much as possible Message-ID: <20191122032422.GK16867@sasha-vm> References: <20191113015025.9685-1-sashal@kernel.org> <20191113015025.9685-87-sashal@kernel.org> <96753746-79ae-3db2-c6d8-e4d5615c0354@lechnology.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <96753746-79ae-3db2-c6d8-e4d5615c0354@lechnology.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 Wed, Nov 13, 2019 at 10:10:30AM -0600, David Lechner wrote: >On 11/12/19 7:48 PM, Sasha Levin wrote: >>From: David Lechner >> >>[ Upstream commit aea4762fb46e048c059ff49565ee33da07c8aeb3 ] >> >>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.) >> >>This patch slows down the SPI as much as possible (if CPU is at 456MHz, >>SPI runs at 1/2 of that, so 228MHz and has a max prescalar of 256, so >>we could get ~891kHz, but we're just rounding it to 1MHz). We also use >>the max allowable value for WDELAY to slow things down even more. >> >>These changes reduce the error of the analog values to about 5mV, which >>is tolerable. >> >>Commits a3762b13a596 ("spi: spi-davinci: Add support for SPI_CS_WORD") >>and e2540da86ef8 ("iio: adc: ti-ads7950: use SPI_CS_WORD to reduce >>CPU usage") introduce changes that allow DMA transfers to be used, so >>this slow down is needed now. >> > >I doubt that the commits above would be backported, so it does not >make sense to backport this patch. I've dropped it, thanks! -- Thanks, Sasha