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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 B9E57C07E99 for ; Fri, 9 Jul 2021 19:22:03 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6BA7C613CA for ; Fri, 9 Jul 2021 19:22:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6BA7C613CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 359CE4011D; Fri, 9 Jul 2021 19:22:03 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id St8lFl1WwMvl; Fri, 9 Jul 2021 19:22:01 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [IPv6:2605:bc80:3010:104::8cd3:938]) by smtp2.osuosl.org (Postfix) with ESMTPS id 5C6B5400C4; Fri, 9 Jul 2021 19:22:01 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3D383C001A; Fri, 9 Jul 2021 19:22:01 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3DBF6C000E for ; Fri, 9 Jul 2021 19:22:00 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 23585423E1 for ; Fri, 9 Jul 2021 19:22:00 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id n12khdsBKhS3 for ; Fri, 9 Jul 2021 19:21:58 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp4.osuosl.org (Postfix) with ESMTP id 0B2DD423D1 for ; Fri, 9 Jul 2021 19:21:57 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3396531B; Fri, 9 Jul 2021 12:21:57 -0700 (PDT) Received: from [10.57.33.207] (unknown [10.57.33.207]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B38DD3F66F; Fri, 9 Jul 2021 12:21:52 -0700 (PDT) Subject: Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC To: Joerg Roedel , Doug Anderson References: <20210624171759.4125094-1-dianders@chromium.org> From: Robin Murphy Message-ID: <0a2042ff-1604-d32d-35a7-d4df8f591459@arm.com> Date: Fri, 9 Jul 2021 20:21:46 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-GB Cc: Ulf Hansson , Linux Doc Mailing List , Peter Zijlstra , linux-pci@vger.kernel.org, Konrad Dybcio , LKML , Thierry Reding , Joel Fernandes , Rajat Jain , Will Deacon , Rob Clark , Saravana Kannan , Jonathan Corbet , quic_c_gdjako@quicinc.com, Linux ARM , Viresh Kumar , Veerabhadrarao Badiganti , "Paul E. McKenney" , linux-arm-msm , Bjorn Helgaas , Sonny Rao , Vlastimil Babka , Randy Dunlap , Linux MMC List , Adrian Hunter , iommu@lists.linux-foundation.org, Andrew Morton , "Maciej W. Rozycki" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2021-07-08 09:08, Joerg Roedel wrote: > On Wed, Jul 07, 2021 at 01:00:13PM -0700, Doug Anderson wrote: >> a) Nothing is inherently broken with my current approach. >> >> b) My current approach doesn't make anybody terribly upset even if >> nobody is totally in love with it. > > Well, no, sorry :) > > I don't think it is a good idea to allow drivers to opt-out of the > strict-setting. This is a platform or user decision, and the driver > should accept whatever it gets. > > So the real question is still why strict is the default setting and how > to change that. It's occurred to me whilst hacking on the relevant area that there's an important point I may have somewhat glossed over there: most of the IOMMU drivers that are used for arm64 do not take advantage of non-strict mode anyway. If anything it would be detrimental, since iommu-dma would waste a bunch of time and memory managing flush queues and firing off the batch invalidations while internally the drivers are still invalidating each unmap synchronously. Those IOMMUs in mobile and embedded SoCs are also mostly used for media devices, where the buffers are relatively large and change relatively infrequently, so they are less likely to gain significantly from supporting non-strict mode. It's primarily the Arm SMMUs which get used in the more "x86-like" paradigm (especially in larger systems) of being stuck in front of everything including networking/storage/PCIe/etc. where the workloads are far more varied. Robin. > Or document for the users that want performance how to > change the setting, so that they can decide. > > Regards, > > Joerg > > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu