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


    FUJITA Tomonori wrote:
    > On Wed, 23 Jul 2008 07:19:43 -0400
    > Prarit Bhargava <prarit@redhat.com> 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."
    >>
    >> 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.
    >>
    >
    > Hmm, you don't fix anything in the helper code. You just use
    > __ALIGN_MASK.
    >
    >
    Yeah -- I meant "fixup" as opposed to fix.

    > And please don't use __ALIGN_MASK. You will notice that no one in
    > mainline use __ALIGN_MASK. Andrew said that we should not.
    >
    > Ideally, we should use ALIGN here but the current code was accepted
    > because it is pretty simple and we have an comment what we do here. So
    > please let it alone.
    >

    I'll resubmit shortly ...

    P.


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