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    Subjectdrm + 4GB RAM + swiotlb = drm craps out
    Okay I've got a bug reported before and now again about > 4GB + radeon
    blows up the DRM... on Intel hw...

    What the drm currently does for the PCI GART table is it allocates a
    chunk of memory (8MB) with vmalloc_32(), then when it decides to use
    it it goes through every page of it calls pci_map_single() (with
    PCI_DMA_TODEVICE, which is probably wrong...) with every page from the
    vmalloc mapping and puts the bus addresses of the pages into the PCI
    GART table on the GPU.

    So when swiotlb happens, as you can guess it all falls apart as the
    drm never calls sync functions at any stage...

    The main problem is the ring buffer and scratch write back, these
    values are read/write from both the CPU and GPU quite a lot, so this
    leads me to think I should really just be using dma_alloc_coherent for
    the whole lot, however this is an 8MB mapping and possibly could be
    getting larger in the future and dynamic as we do dynamic PCIEGART
    support for the radeons...

    So I suppose I'm asking for ideas on the "correct" way to do this, and
    perhaps any quick way to patch up the problem I'm seeing now by making
    swiotlb not get involved ....

    Regards,
    Dave.
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