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 7777BC636D7 for ; Wed, 22 Feb 2023 01:30:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230136AbjBVBaZ (ORCPT ); Tue, 21 Feb 2023 20:30:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44320 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229591AbjBVBaX (ORCPT ); Tue, 21 Feb 2023 20:30:23 -0500 Received: from codeconstruct.com.au (pi.codeconstruct.com.au [203.29.241.158]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9E21A2E806 for ; Tue, 21 Feb 2023 17:30:22 -0800 (PST) Received: from pecola.lan (unknown [159.196.93.152]) by mail.codeconstruct.com.au (Postfix) with ESMTPSA id 56D4620037; Wed, 22 Feb 2023 09:30:15 +0800 (AWST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=codeconstruct.com.au; s=2022a; t=1677029417; bh=dKZoLqo3DWoAawVA6U++xyewr4VS6v9UTkeXqOdFT80=; h=Subject:From:To:Date:In-Reply-To:References; b=LaMXyIwenqXd2NJpLNx0MJWu44XaaWS+XoUVQz1QhWfj6xROwysPYi4xLGrQNIf/8 3vMdoH/XGf9BY2b37v5F1QSMq0cOaM/bRejMzgxCBWb+EpSqp3qrsUAIBSoOz2ekzq afvd5hPg4g2SVmF5w8+dnhmkD1NRVTkFb8LARY9UlHW/Bld2O+r5NReLqZ3jcQyKV6 HvUuqLCN+/WPxMcvoEsirCy6QG5UmLNor+K4ZgH0IpmSaJTWCl+6aqq8qpL7mnlgXK vW7ZmjerwzWwIFBVlswQLy7YN6BqYtRYWa/FXjmk15FM/qCRtgbwGHVEx++XRWMHyZ hweZA1/lDrgsQ== Message-ID: Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2 From: Jeremy Kerr To: Ryan Chen , Rob Herring , Krzysztof Kozlowski , Joel Stanley , Andrew Jeffery , Philipp Zabel , "openbmc@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "linux-aspeed@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" Date: Wed, 22 Feb 2023 09:30:14 +0800 In-Reply-To: References: <20230220061745.1973981-1-ryan_chen@aspeedtech.com> <20230220061745.1973981-2-ryan_chen@aspeedtech.com> <2141e513acc750bf26775f5b435f4dccd41244aa.camel@codeconstruct.com.au> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.46.3-1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ryan, > > On the other hand, if it's just because of OS behaviour, then this > > doesn't belong > > in the DT. > >=20 > > Maybe to help us understand: why would you ever *not* want DMA > > mode? > > Isn't that always preferable? > In AST SOC i2c design is 16 i2c bus share one dma engine.=20 Does this mean that only one i2c controller in the system can be configured to use DMA? Or is it able to be shared between multiple controllers? > It can be switch setting by dts setting. Otherwise driver by default > probe is DMA mode. You've explained what the modes do, and how they're switched, and what the default is. However this doesn't explain *why* someone would want to choose a particular mode when creating a controller node. Still with the question above: assuming there are no restrictions on DMA usage, why wouldn't a driver implementation just enable it always? Cheers, Jeremy