On Wed, Jul 19, 2017 at 4:55 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote: > On 19/07/17 12:17, Anup Patel wrote: >> On Wed, Jul 19, 2017 at 4:27 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote: >>> On 19/07/17 10:33, Anup Patel wrote: >>>> This patchset primarily adds Broadcom FlexRM reset module for >>>> VFIO platform driver. We also have minor improvments in IOMMU >>>> and VFIO driver to allow VFIO no-IOMMU mode access to FlexRM. >>> >>> I'm struggling to understand the IOMMU changes here - what's the >>> FlexRM's hardware relationship with the IOMMU, and how is it different >>> from any other device? Furthermore, if there *is* a relevant IOMMU >>> present, why would no-IOMMU mode need to be involved at all? >> >> We want to have FlexRM device accessible from user-space >> using VFIO platform with and without IOMMU. >> >> Currently, if IOMMU ops are available for platform bus then >> I cannot access FlexRM device using VFIO no-IOMMU mode. > > So does the FlexRM hardware master through the SMMU or not? If it does, > why do you need no-IOMMU mode? If it doesn't, then that's yet another > reason to fix the real problem, which is the utterly broken notion of > there being 'an IOMMU' on the platform 'bus', rather than papering over > it in VFIO. > We are not trying to paper-over the issue. The ARM SMMU will have limited number of SMRs so on a big SOC with large number of DMA-capable devices we can run-out of SMRs if we try to configure SMMU for all DMA-capable devices. Regards, Anup
