Messages in this thread | | | Date | Mon, 30 Jan 2023 16:35:35 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device |
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On Mon, Jan 30, 2023 at 12:04:33PM -0800, Nicolin Chen wrote:
> I recall we've discussed this that SMMU sets up domain when it > attaches the device to, so we made a compromise here...
The ARM driver has a problem that it doesn't know what SMMU instance will host the domain when it is allocated so it doesn't know if it should select a S1 or S2 page table format - which is determined by the capabilities of the specific SMMU HW block.
However, we don't have this problem when creating the S2. The S2 should be created by a special alloc_domain_iommufd() asking for the S2 format. Not only does the new alloc_domain_iommufd API directly request a S2 format table, but it also specifies the struct device so any residual details can be determined directly.
Thus there is no need to do the two stage process when working with the S2.
So fixup the driver to create fully configured iommu_domain's immediately and get rid of this problem.
IMHO I would structure the smmu driver so that all the different iommu_domain formats have their own ops pointer. The special "undecided" format would have a special ops with only attach_dev and at first attach it would switch the ops to whatever format it selected.
I think this could get rid of a lot of the 'if undecided/S1/S2/CD' complexity all over the place. You know what type it is because you were called on a op that is only called on its type.
Jason
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