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    SubjectRe: [RFC] MMIO accessors & barriers documentation
    Date
    Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:

    > I've not gone too much in details about write combining (we need to do
    > something about it but I don't want to mix problems) but I did define
    > that the ordered accessors aren't guaranteed to provide write combining
    > on storage mapped with WC enabled while the relaxed or non ordered ones
    > are. That should be enough at this point.

    Sounds good.

    > Later, we should look into providing an ioremap_wc() and possibly page
    > table flags for write combining userland mappings. Time to get rid of
    > MTRRs for graphics :) And infiniband-style stuff seems to want that too.

    ioremap_wc is actually the easy half. I have an old patch that handles
    that. The trick is to make certain multiple people don't map the same
    thing with different attributes. Unfortunately I haven't had time to
    work through that one yet.

    Eric

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