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    SubjectRe: [PATCH] Document Linux's memory barriers [try #4]
    Alan Cox writes:

    > On Fri, Mar 10, 2006 at 10:34:53AM +1100, Paul Mackerras wrote:
    > > MMIO accesses are done under a spinlock, and that if your driver is
    > > missing them then that is a bug. I don't think it makes sense to say
    > > that mmiowb is required "on some systems".
    >
    > Agreed. But if it is missing it may not be a bug. It depends what the lock
    > actually protects.

    True. What I want is a statement that if one of the purposes of the
    spinlock is to provide ordering of the MMIO accesses, then leaving out
    the mmiowb is a bug. I want it to be like the PCI DMA API in that
    drivers are required to use it even on platforms where it's a no-op.

    Paul.

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