Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932474AbdGSL3U (ORCPT ); Wed, 19 Jul 2017 07:29:20 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38510 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932300AbdGSL3S (ORCPT ); Wed, 19 Jul 2017 07:29:18 -0400 Subject: Re: [PATCH 1/5] iommu: Add capability IOMMU_CAP_BYPASS To: Anup Patel , Will Deacon Cc: Joerg Roedel , Baptiste Reynal , Alex Williamson , Scott Branden , Linux Kernel , Linux ARM Kernel , Linux IOMMU , kvm@vger.kernel.org, BCM Kernel Feedback References: <1500456838-18405-1-git-send-email-anup.patel@broadcom.com> <1500456838-18405-2-git-send-email-anup.patel@broadcom.com> <675744d3-b070-1245-6ebc-579c4b5f4a75@arm.com> <20170719112315.GE13642@arm.com> From: Robin Murphy Message-ID: <0945502b-3962-15cf-bc9f-6ae9c5470a30@arm.com> Date: Wed, 19 Jul 2017 12:29:14 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1725 Lines: 43 On 19/07/17 12:26, Anup Patel wrote: > On Wed, Jul 19, 2017 at 4:53 PM, Will Deacon wrote: >> On Wed, Jul 19, 2017 at 04:49:00PM +0530, Anup Patel wrote: >>> On Wed, Jul 19, 2017 at 4:28 PM, Robin Murphy wrote: >>>> On 19/07/17 10:33, Anup Patel wrote: >>>>> Some of the IOMMUs (such as ARM SMMU) are capable of bypassing >>>>> transactions for which no IOMMU domain is configured. >>>>> >>>>> This patch adds IOMMU_CAP_BYPASS which can be used by IOMMU >>>>> drivers to advertise transation bypass capability of an IOMMU. >>>> >>>> Whatever the intended semantics of this are, I can't help thinking it >>>> would be better served by allowing callers to explicitly allocate their >>>> own IOMMU_DOMAIN_IDENTITY domains. That would also be useful for the >>>> problem we have with legacy virtio devices behind real IOMMUs. >>> >>> We want to use VFIO no-IOMMU mode for FlexRM device but >>> currently it does not allow on our SOC because IOMMU ops are >>> registered for platform bus. >> >> Why do you want to use no-IOMMU mode if you have an IOMMU, and why you do >> think the individual IOMMU drivers are the place to implement this? >> >> NAK to the SMMU patches, for the reasons outlined by Robin. > > We have limited number of SMRs on our SOC. > > There are lot of devices for which we can potentially > configure SMMU but then due to limited number of > SMRs so we use SMMU only for certain devices. Is the stream ID allocation so whacked out that you can't use masking? Robin. > For FlexRM device on our SOC, we don't intend to > use SMMU hence we need VFIO no-IOMMU mode > working for FlexRM device on our SOC. > > Please re-consider your NAK. > > Regards, > Anup >