> From: Robin Murphy <robin.murphy@xxxxxxx> > Sent: Wednesday, June 22, 2022 3:55 PM > > On 2022-06-16 23:23, Nicolin Chen wrote: > > On Thu, Jun 16, 2022 at 06:40:14AM +0000, Tian, Kevin wrote: > > > >>> The domain->ops validation was added, as a precaution, for mixed- > driver > >>> systems. However, at this moment only one iommu driver is possible. So > >>> remove it. > >> > >> It's true on a physical platform. But I'm not sure whether a virtual > platform > >> is allowed to include multiple e.g. one virtio-iommu alongside a virtual VT- > d > >> or a virtual smmu. It might be clearer to claim that (as Robin pointed out) > >> there is plenty more significant problems than this to solve instead of > simply > >> saying that only one iommu driver is possible if we don't have explicit > code > >> to reject such configuration. 😊 > > > > Will edit this part. Thanks! > > Oh, physical platforms with mixed IOMMUs definitely exist already. The > main point is that while bus_set_iommu still exists, the core code > effectively *does* prevent multiple drivers from registering - even in > emulated cases like the example above, virtio-iommu and VT-d would both > try to bus_set_iommu(&pci_bus_type), and one of them will lose. The > aspect which might warrant clarification is that there's no combination > of supported drivers which claim non-overlapping buses *and* could > appear in the same system - even if you tried to contrive something by > emulating, say, VT-d (PCI) alongside rockchip-iommu (platform), you > could still only describe one or the other due to ACPI vs. Devicetree. > This explanation is much clearer! thanks.
