Messages in this thread | | | From | Hiroshi Doyu <> | Date | Tue, 24 Jan 2012 12:36:14 +0100 | Subject | Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver |
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From: Joerg Roedel <joerg.roedel@amd.com> Subject: Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver Date: Tue, 24 Jan 2012 12:04:44 +0100 Message-ID: <20120124110444.GB19255@amd.com>
> > > Hmm, this looks like there is a 1-1 mapping between hardware SMMU > > > devices and domains. This is not consistent with IOMMU-API semantics > > > where a domain can contain devices behind different SMMUs. Please fix > > > that. > > > > I'm a bit confused with the concept of "domain". I thought that > > "domain" is equivalent to a "virtual address space". Usually a IOMMU > > device provides a virtual address space for multiple client > > devices. IOW, a IOMMU device provides a virtual address space, which > > can be shared with multiple client devices. > > > > Actually Tegra SMMU case, a single IOMMU device has 4 different > > virtual address speace("smmu_as"). Each "smmu_as" has its own virtual > > address space. "smmu_as[i]" has mutiple "smmu_client" devices. > > > > smmu_as[i] == domain[i] > > > > I don't understand why "a domain can contain devices behind different > > SMMUs" because those client devices belong to different virtual > > address spaces, and they should belong to different "domains". > > > > Could you please explain a bit more about "domain"? > > A domain is, as you said, a virtual address space for IO devices. But > the important point is, an arbitrary number of devices can be part of a > domain. This also means that the devices can be behind different > hardware SMMUs. In this case your driver needs to program the page-table > pointer into more than one SMMU to give devices behind different SMMUs > the same address space.
Thank you for explaining.
Does the above mean that a buffer can be shared with different devices which belong to different IOMMU devices(virtual address spaces)?
For example, assuming the following:
- We have "struct iommu_domain *domain1". - "domain1" has iommu device "iommu_dev1" and "iommu_dev2". - "iommu_dev1" has "client_dev1" and "client_dev2". - "iommu_dev2" has "client_dev3" and "client_dev4".
"iommu_map(domain1, iova, pa, ...)" will create the following mapping ___at once___:
- (iova)-(pa) mapping in iommu_dev1(iommmu_dev1's virtual address space) - (iova)-(pa) mapping in iommu_dev2(iommmu_dev2's virtual address space)
Is the above correct?
It seems that the same (iova) is used for different virtual address spaces. What kind of case is this beneficial most in?
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