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Date: Fri, 21 Dec 2007 10:49:45 +1100 From: Benjamin Herrenschmidt <benh@....ibm.com> To: Steve Wise <swise@...ngridcomputing.com> Cc: benh@...abs.au.ibm.com, Roland Dreier <rdreier@...co.com>, linux-kernel@...r.kernel.org, OpenFabrics General <general@...ts.openfabrics.org>, Benjamin Herrenschmidt <bherren@....ibm.com>, Wen Xiong <wenxiong@...ibm.com>, Olof Johansson <olof@...om.net>, Paul Mackerras <pmac@....ibm.com> Subject: Re: iommu dma mapping alignment requirements > Sounds good. Thanks! > > Note, that these smaller sub-host-page-sized mappings might pollute the > address space causing full aligned host-page-size maps to become > scarce... Maybe there's a clever way to keep those in their own segment > of the address space? We already have a large vs. small split in the iommu virtual space to alleviate this (though it's not a hard constraint, we can still get into the "other" side if the default one is full). Try that patch and let me know: Index: linux-work/arch/powerpc/kernel/iommu.c =================================================================== --- linux-work.orig/arch/powerpc/kernel/iommu.c 2007-12-21 10:39:39.000000000 +1100 +++ linux-work/arch/powerpc/kernel/iommu.c 2007-12-21 10:46:18.000000000 +1100 @@ -278,6 +278,7 @@ int iommu_map_sg(struct iommu_table *tbl unsigned long flags; struct scatterlist *s, *outs, *segstart; int outcount, incount, i; + unsigned int align; unsigned long handle; BUG_ON(direction == DMA_NONE); @@ -309,7 +310,11 @@ int iommu_map_sg(struct iommu_table *tbl /* Allocate iommu entries for that segment */ vaddr = (unsigned long) sg_virt(s); npages = iommu_num_pages(vaddr, slen); - entry = iommu_range_alloc(tbl, npages, &handle, mask >> IOMMU_PAGE_SHIFT, 0); + align = 0; + if (IOMMU_PAGE_SHIFT < PAGE_SHIFT && (vaddr & ~PAGE_MASK) == 0) + align = PAGE_SHIFT - IOMMU_PAGE_SHIFT; + entry = iommu_range_alloc(tbl, npages, &handle, + mask >> IOMMU_PAGE_SHIFT, align); DBG(" - vaddr: %lx, size: %lx\n", vaddr, slen); @@ -572,7 +577,7 @@ dma_addr_t iommu_map_single(struct iommu { dma_addr_t dma_handle = DMA_ERROR_CODE; unsigned long uaddr; - unsigned int npages; + unsigned int npages, align; BUG_ON(direction == DMA_NONE); @@ -580,8 +585,13 @@ dma_addr_t iommu_map_single(struct iommu npages = iommu_num_pages(uaddr, size); if (tbl) { + align = 0; + if (IOMMU_PAGE_SHIFT < PAGE_SHIFT && + ((unsigned long)vaddr & ~PAGE_MASK) == 0) + align = PAGE_SHIFT - IOMMU_PAGE_SHIFT; + dma_handle = iommu_alloc(tbl, vaddr, npages, direction, - mask >> IOMMU_PAGE_SHIFT, 0); + mask >> IOMMU_PAGE_SHIFT, align); if (dma_handle == DMA_ERROR_CODE) { if (printk_ratelimit()) { printk(KERN_INFO "iommu_alloc failed, " -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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