On Wed, Mar 23, 2011 at 05:08:45AM -0400, Abhilash Kesavan wrote: > We are investigating if the generic IOMMU API (include/linux/iommu.h) > can be used for the IOMMU on our arm-based boards. Great :-) > I noticed that msm's IOMMU code (arch/arm/mach-msm/iommu.c) uses the > genric IOMMU API and have a few queries regarding the supported > features. Following are some features/requirements of our system: > > 1) Multiple IOMMU's - consistency between parallel IOMMUs must be maintained This is hidden behind the API. The IOMMU driver is responsible for managing multiple IOMMUs. On x86 there is a unique device<->IOMMU relationship which is used internally in the drivers. Users of the IOMMU-API can ignore the fact that there are multiple IOMMUs in the system. > 2) Supports varying page sizes - 4K, 64K, 1M, 16M i.e. a sg list of > contiguous physical memory blocks be made available. Thus, giving us > mappings from the conservative 4K to large1M reducing TLB misses. This is supported but also hidden in the IOMMU driver implementation. the AMD-IOMMU driver implements multiple page-sizes already using this API. The API user has a function which looks as follows: int iommu_map(struct iommu_domain *domain, unsigned long iova, phys_addr_t paddr, int gfp_order, int prot); this function needs to map the pysically contiguous memory starting at paddr at the io-virtual address iova. The size of the mapping is determinded by the gfp_order parameter. The size of the mapping is basically (2**(gfp_order))*PAGE_SIZE. Note that PAGE_SIZE is the cpu page-size. The IOMMU driver has enough information from that function to map the area with the best-fit page-sizes. > 3) Multiple VA allocations can be associated with the same PA space. I don't really understand what you mean here. Can you elabortate? > Who manages the virtual address space of IO device that has IOMMU? I > think the generic iommu.h API cannot handle virtual address space and > memory allocation. Is it just a IOMMU handler? Should we have another > virtual memory manager for IOMMU? The layout of the virtual address space for the IO device needs to be managed by the particular device driver. The IOMMU-API only provides functions for mapping/unmapping memory. Regards, Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
