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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A99CCC61DA3 for ; Wed, 22 Feb 2023 01:31:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:To:From:Subject:Message-ID:Reply-To:Cc:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=DzrURmB5VJkxWMgUOiy78eb1qqYe3Pi92+CwvU5w83g=; b=KF78Fpbq+muZGQ eiX+NkfccyN65b+bxk3meN7LjlH+78Pw6ofSZKPWptf9Cy6zPKcNhNTtbD0+EZIhNrxy62bbrv3Jh V4npOiqxHq62+D3If/jc34P/F4gf40DCingIZ5OAsrHzqxc1CoyqH2DbI+jhYyehG+Wne8HkF+IMV 9YVUNP8dH0ez3JxK7fe7DIxdEswWsK1Z0GARBzW5AazR740e7WEDpvB41bkeo7aSsieWtq0pexkEF 1v8ckq/JWGHFPUOn3z7+/i5M86bFO7KmvWzmQ74p9nSu5MdrnyaNT457X95pHg1W1DVtmPKEUcC5a Qds8PJOtzEOUc0jPDvSw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pUdxn-00AL97-Bv; Wed, 22 Feb 2023 01:30:31 +0000 Received: from pi.codeconstruct.com.au ([203.29.241.158] helo=codeconstruct.com.au) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pUdxk-00AL7a-74 for linux-arm-kernel@lists.infradead.org; Wed, 22 Feb 2023 01:30:29 +0000 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> User-Agent: Evolution 3.46.3-1 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230221_173028_466960_D69CDECF X-CRM114-Status: GOOD ( 13.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ryan, > > On the other hand, if it's just because of OS behaviour, then this > > doesn't belong > > in the DT. > > > > 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. 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel