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=-5.6 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 54A19C11F68 for ; Tue, 13 Jul 2021 18:07:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 383D761369 for ; Tue, 13 Jul 2021 18:07:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233676AbhGMSKC (ORCPT ); Tue, 13 Jul 2021 14:10:02 -0400 Received: from foss.arm.com ([217.140.110.172]:48602 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229478AbhGMSKB (ORCPT ); Tue, 13 Jul 2021 14:10:01 -0400 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 243A61FB; Tue, 13 Jul 2021 11:07:11 -0700 (PDT) Received: from [10.57.36.240] (unknown [10.57.36.240]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C0FC43F7D8; Tue, 13 Jul 2021 11:07:05 -0700 (PDT) Subject: Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC To: Doug Anderson , Joerg Roedel Cc: Will Deacon , Bjorn Andersson , Ulf Hansson , Adrian Hunter , Bjorn Helgaas , John Garry , Rob Clark , quic_c_gdjako@quicinc.com, Saravana Kannan , Rajat Jain , Sai Prakash Ranjan , Veerabhadrarao Badiganti , Linux MMC List , linux-arm-msm , linux-pci@vger.kernel.org, "list@263.net:IOMMU DRIVERS" , Joerg Roedel , iommu@lists.linux-foundation.org, Sonny Rao , Joel Fernandes , Andrew Morton , Jonathan Corbet , Jordan Crouse , Konrad Dybcio , Krishna Reddy , "Maciej W. Rozycki" , Nicolin Chen , "Paul E. McKenney" , Peter Zijlstra , Randy Dunlap , Thierry Reding , Viresh Kumar , Vlastimil Babka , Linux ARM , Linux Doc Mailing List , LKML References: <20210624171759.4125094-1-dianders@chromium.org> From: Robin Murphy Message-ID: Date: Tue, 13 Jul 2021 19:07:00 +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-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2021-07-08 15:36, Doug Anderson wrote: [...] >> Or document for the users that want performance how to >> change the setting, so that they can decide. > > Pushing this to the users can make sense for a Linux distribution but > probably less sense for an embedded platform. So I'm happy to make > some way for a user to override this (like via kernel command line), > but I also strongly believe there should be a default that users don't > have to futz with that we think is correct. FYI I did make progress on the "punt it to userspace" approach. I'm not posting it even as an RFC yet because I still need to set up a machine to try actually testing any of it (it's almost certainly broken somewhere), but in the end it comes out looking surprisingly not too bad overall. If you're curious to take a look in the meantime I put it here: https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/fq Cheers, Robin.