On Sun, 17 Aug 2008 14:56:14 +0200 Ingo Molnar <mingo@xxxxxxx> wrote: > > * FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > > > > Config is: > > > > > > http://redhat.com/~mingo/misc/config-Fri_Aug_15_18_30_56_CEST_2008.bad > > > > > > Any idea why that is so? Apparently the alignment change wasnt as benign > > > as assumed. > > > > Ah, sorry, > > > > @@ -262,7 +264,11 @@ static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem, > > static dma_addr_t > > gart_map_simple(struct device *dev, phys_addr_t paddr, size_t size, int dir) > > { > > - dma_addr_t map = dma_map_area(dev, paddr, size, dir); > > + dma_addr_t map; > > + unsigned long align_mask; > > + > > + align_mask = (roundup_pow_of_two(size) >> PAGE_SHIFT) - 1; > > + map = dma_map_area(dev, paddr, size, dir, align_mask); > > > > This code doesn't work with the case size < PAGE_SIZE. > > > > I think that dmam_alloc_consistent in libata-core fails due to this > > bug. > > > > Can you try this? > > ok - merged the commit below in tip/x86/iommu. > > > BTW, I think that this is not urgent stuff at all. > > ok - i've queued it up for v2.6.28. > > Ingo > > --------------> > From 4ae29849888f85a0cee12553995d47ec527ad049 Mon Sep 17 00:00:00 2001 > From: Prarit Bhargava <prarit@xxxxxxxxxx> > Date: Sat, 16 Aug 2008 10:15:32 +0900 > Subject: [PATCH] x86 gart: allocate size-aligned address for alloc_coherent, v2 > > pci_alloc_consistent/dma_alloc_coherent does not return size aligned > addresses. > > >From Documentation/DMA-mapping.txt: > > "pci_alloc_consistent returns two values: the virtual address which you > can use to access it from the CPU and dma_handle which you pass to the > card. > > The cpu return address and the DMA bus master address are both > guaranteed to be aligned to the smallest PAGE_SIZE order which > is greater than or equal to the requested size. This invariant > exists (for example) to guarantee that if you allocate a chunk > which is smaller than or equal to 64 kilobytes, the extent of the > buffer you receive will not cross a 64K boundary." > > 1. Modify alloc_iommu to allow for an alignment mask > 2. Modify pci_gart_simple to return size-aligned values. > 3. Fixup the alignment calculation in the iommu-helper code. > 4. Fix possible overflow in alloc_iommu's boundary_size calculation. > (It is possible that alloc_iommu()'s boundary_size overflows as > dma_get_seg_boundary can return 0xffffffff. In that case, further usage of > boundary_size triggers a BUG_ON() in the iommu code.) > > End result: When allocating from IOMMU, pci_alloc_consistent/dma_alloc_coherent > will now return a size aligned value. The above commit log of Prarit's patch is completely wrong (so I wrote this patch). To avoid misunderstanding, can you apply this patch with a proper description like this: = This patch changes GART IOMMU to return a size aligned address wrt dma_alloc_coherent, as DMA-mapping.txt defines: The cpu return address and the DMA bus master address are both guaranteed to be aligned to the smallest PAGE_SIZE order which is greater than or equal to the requested size. This invariant exists (for example) to guarantee that if you allocate a chunk which is smaller than or equal to 64 kilobytes, the extent of the buffer you receive will not cross a 64K boundary. But it is very unlikely that this matters. As DMA-mapping.txt explains, This invariant is to avoid the boundary problem (such as 64K). Now the majority of IOMMUs including GART (except for Intel IOMMU) don't allocate a buffer that crosses a 64K boundary wrt all the DMA mapping interfaces (dma_alloc_coherent, dma_map_sg, and dma_map_single) because of segment_boundary_mask in struct device_dma_parameters. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
