Messages in this thread |  | | | Date | Thu, 20 Dec 2007 13:11:28 -0600 | | From | Steve Wise <> | | Subject | Re: [ofa-general] iommu dma mapping alignment requirements |
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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?
Steve.
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