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    SubjectRe: IOMMU and graphics cards
    On Thu, May 07, 2009 at 07:23:33PM +0900, FUJITA Tomonori wrote:
    > On Thu, 7 May 2009 12:01:14 +0200
    > Joerg Roedel <joerg.roedel@amd.com> wrote:
    >
    > > > Do you meant that AMD IOMMU code use the bitmap each device to manage
    > > > address space so enlarging the DMA address space wastes memory?
    > >
    > > Its not only the bitmap. There are also the page tables that would waste
    > > memory if the aperture in the AMD IOMMU driver is enlarged to, say, 4GB.
    > > Most devices don't need such a large amount of DMA address space. As I
    > > found out VT-d does not have this problem because they implemented
    > > another allocator which can cover all possible memory.
    > > For the AMD IOMMU I currently implement a kind of a dynamically growing
    > > bitmap allocator to fix this problem.
    >
    > Yeah, I know the deference. Well, I like the AMD IOMMU driver's
    > property that dma mapping doesn't fail in OOM but I understand why you
    > want such daynamically growing.

    Well, I will try to minimize the impact. Current plan is to preallocate
    bitmap and page tables for 128MB of DMA address space. Everything beyond
    that will be allocated on demand.

    > > > > But unless this problem isn't solved the
    > > > > drivers won't be fixed, I guess.
    > > > > I guess the DRM code in the kernel may have the same problem with IOMMU
    > > > > enabled?
    > > >
    > > > Looks like the DRM code uses the DMA API.
    > >
    > > The proprietary drivers make problems so far. For the ATI one I am in
    > > contact with the developers to try to fix it. But I can't do anything
    > > about the other proprietary driver I am aware of :-(
    >
    > I don't know anything about the graphic drivers but are there any
    > other proprietary drivers except for ATI and AMD? Fixing only two
    > drivers to make the majority happy?

    At least Nvidia comes to my mind. Not sure about other graphic card
    vendors...

    Joerg

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