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    SubjectRe: MMIO and gcc re-ordering issue


    On Tue, 3 Jun 2008, Nick Piggin wrote:
    >
    > Linus: on x86, memory operations to wc and wc+ memory are not ordered
    > with one another, or operations to other memory types (ie. load/load
    > and store/store reordering is allowed). Also, as you know, store/load
    > reordering is explicitly allowed as well, which covers all memory
    > types. So perhaps it is not quite true to say readl/writel is strongly
    > ordered by default even on x86. You would have to put in some
    > mfence instructions in them to make it so.

    Well, you have to ask for WC/WC+ anyway, so it's immaterial. A driver that
    does that needs to be aware of it. IOW, it's a non-issue, imnsho.

    Linus


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