On Wed, Jul 19, 2017 at 04:56:38PM +0530, Anup Patel wrote: > On Wed, Jul 19, 2017 at 4:53 PM, Will Deacon <will.deacon@xxxxxxx> 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 <robin.murphy@xxxxxxx> 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. > > 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. I'm afraid it still stands for the current implementation. If you can't solve the SMR restriction by grouping things appropriately (which would be my strong preference), then I think you'll have to follow-up on Robin's suggestion of implementing support for IDENTITY domains in VFIO for no-IOMMU mode to be used even when an IOMMU is present. Will
