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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