Re: [PATCH]: PCI: GART iommu alignment fixes [v2]

From: Joerg Roedel
Date: Wed Jul 23 2008 - 18:10:46 EST

On Wed, Jul 23, 2008 at 07:19:43AM -0400, Prarit Bhargava wrote:
> 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."

Interesting. Have you experienced any problems because of that
misbehavior in the GART code? AMD IOMMU currently also violates this
requirement. I will send a patch to fix that there too.


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