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    SubjectRe: [PATCH] RFC: kills consistent_dma_mask
    > From: Krzysztof Halasa <>
    > Date: 18 Aug 2003 00:34:17 +0200

    > It's unneeded (it can be easily done in a driver, should a need arrive,
    > without polluting the PCI subsystem) and is not supported by "DMA" API.

    Are you talking about doing tripple calls, e.g.

    pci_set_dma_mask(pdev, 0xFFFFFFFF);
    foo = pci_alloc_consistent(pdev, size, &handle);
    // Restore for upcoming streaming allocations
    pci_set_dma_mask(pdev, 0xFFFFFFFFFFFFFFFF);

    Possibly Jes considered that alternative and decided that it
    did not allow for sufficient performance.

    > It isn't even implemented on most platforms - only x86_64 and ia64 have
    > support for it, while on the remaining archs using it according to the
    > docs (with non-default value) could mean Oops or something like that.

    Before you go for that, I'd rather see you implementing the
    double/tripple calls in drivers, check for effects, THEN
    go for removal of the mask. If you cannot do it, plea SGI people
    to test it on SN-2 for you (or same for Intel Tiger box).

    > This patch doesn't actually change any current kernel behaviour.

    Sure it does. It blows all non-mmu ia64 out of the water.

    The consistent mask looks a little distasteful to me, and I think
    it should not buy us performance because consistent allocations
    are not supposed to be fast. They are bad, but what you are doing
    is worse: you are trying to ruin the day of legitimate users.
    Please, be reasonable. Get SGI buy-in and come back.

    -- Pete
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