From: "joerg.roedel@xxxxxxx" <joerg.roedel@xxxxxxx> Subject: Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver Date: Tue, 24 Jan 2012 12:57:23 +0100 Message-ID: <20120124115723.GC19255@xxxxxxx> > On Tue, Jan 24, 2012 at 12:36:14PM +0100, Hiroshi Doyu wrote: > > > 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? > > Yes, this is correct. > > > It seems that the same (iova) is used for different virtual address > > spaces. What kind of case is this beneficial most in? > > It is actually the _same_ virtual address space which is used by > iommu_dev1 and iommu_dev2. Think of it like multiple threads of a single > process. They also share the address space. I see. The above makes more sense. > This is a requirement of the iommu-api which is beneficial for > virtualization and simplifies the usage of the api in general. The user > does not need to care which devices can be assigned to which domain > because of underlying hardware constraints. The goal of the iommu-api is > to hide such contraints. Now it's clear to me. I'll send the update patch soon. Thank you for explaining all of this. > > > Joerg > > -- > AMD Operating System Research Center > > Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach > General Managers: Alberto Bozzo > Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 > -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
