On Mon, Aug 14, 2023 at 04:43:23PM +0800, Baolu Lu wrote: > > This is on github:https://github.com/jgunthorpe/linux/commits/iommu_all_defdom > > It seems that after this series, all ARM iommu drivers are able to > support the IDENTITY default domain, hence perhaps we can remove below > code? Yes, but this code is still used > If I remember it correctly, the background of this part of code is > that some arm drivers didn't support IDENTITY domain, so fall back to > DMA domain if IDENTITY domain allocation fails. Not quite.. if (req_type) return __iommu_group_alloc_default_domain(group, req_type); req_type == 0 can still happen because it depends on what def_domain_type returns, which is still 0 in alot of cases /* The driver gave no guidance on what type to use, try the default */ dom = __iommu_group_alloc_default_domain(group, iommu_def_domain_type); if (dom) return dom; So we try the default which might be IDENTITY/DMA/DMA_FQ - still have to do this. /* Otherwise IDENTITY and DMA_FQ defaults will try DMA */ if (iommu_def_domain_type == IOMMU_DOMAIN_DMA) return NULL; dom = __iommu_group_alloc_default_domain(group, IOMMU_DOMAIN_DMA); if (!dom) return NULL; pr_warn("Failed to allocate default IOMMU domain of type %u for group %s - Falling back to IOMMU_DOMAIN_DMA", iommu_def_domain_type, group->name); And this hunk is primarily a fallback in case the DMA_FQ didn't work. Then we try normal DMA. That it also protected against not implementing IDENTITY is a side effect, so I think we have to keep all of this still. Jason
