On Fri, Feb 21, 2020 at 01:59:15PM +1100, David Gibson wrote: > > Hell no. This is a detail of the platform DMA direct implementation. > > Drivers have no business looking at this flag, and virtio finally needs > > to be fixed to use the DMA API properly for everything but legacy devices. > > So, this patch definitely isn't right as it stands, but I'm struggling > to understand what it is you're saying is the right way. > > By "legacy devices" I assume you mean pre-virtio-1.0 devices, that > lack the F_VERSION_1 feature flag. Is that right? Because I don't > see how being a legacy device or not relates to use of the DMA API. No. "legacy" is anything that does not set F_ACCESS_PLATFORM. > I *think* what you are suggesting here is that virtio devices that > have !F_IOMMU_PLATFORM should have their dma_ops set up so that the > DMA API treats IOVA==PA, which will satisfy what the device expects. > Then the virtio driver can use the DMA API the same way for both > F_IOMMU_PLATFORM and !F_IOMMU_PLATFORM devices. No. Those should just keep using the existing legacy non-dma ops case and be done with it. No changes to that and most certainly no new features.
