From mboxrd@z Thu Jan 1 00:00:00 1970 From: robin.murphy@arm.com (Robin Murphy) Date: Wed, 19 Jul 2017 12:29:14 +0100 Subject: [PATCH 1/5] iommu: Add capability IOMMU_CAP_BYPASS In-Reply-To: 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> Message-ID: <0945502b-3962-15cf-bc9f-6ae9c5470a30@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 >