Messages in this thread | | | Date | Thu, 20 Dec 2007 13:29:41 -0600 | From | Steve Wise <> | Subject | Re: [ofa-general] iommu dma mapping alignment requirements |
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Steve Wise wrote: > Roland Dreier wrote: >> > It appears that my problem boils down to a single host page of memory >> > that is mapped for dma, and the dma address returned by dma_map_sg() >> > is _not_ 64KB aligned. Here is an example: >> >> > My first question is: Is there an assumption or requirement in linux >> > that dma_addressess should have the same alignment as the host address >> > they are mapped to? IE the rdma core is mapping the entire 64KB page, >> > but the mapping doesn't begin on a 64KB page boundary. >> >> I don't think this is explicitly documented anywhere, but it certainly >> seems that we want the bus address to be page-aligned in this case. >> For mthca/mlx4 at least, we tell the adapter what the host page size >> is (so that it knows how to align doorbell pages etc) and I think this >> sort of thing would confuse the HW. >> >> - R. > > > In arch/powerpc/kernel/iommu.c:iommu_map_sg() I see that it calls > iommu_range_alloc() with a alignment_order of 0: > >> vaddr = (unsigned long)page_address(s->page) + s->offset; >> npages = iommu_num_pages(vaddr, slen); >> entry = iommu_range_alloc(tbl, npages, &handle, mask >> >> IOMMU_PAGE_SHIFT, 0); > > But perhaps the alignment order needs to be based on the host page size? >
Or based on the alignment of vaddr actually...
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