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    SubjectRe: Flushing writes to PCI devices
    Alan Stern wrote:
    > I've heard that to insure proper synchronization it's necessary to flush
    > MMIO writes (writel, writew, writeb) to PCI devices by reading from the
    > same area. Is this equally true for I/O-space writes (inl, inw, inb)?
    > What about configuration space writes (pci_write_config_dword etc.)?

    Technically, according to the PCI specification, I/O space writes may be
    posted in the host bus bridge (though unlike MMIO space, not at any
    other PCI bridges) and would require a read in order to flush them.
    However, there seem to be few if any chipsets ever made which actually
    do this for I/O writes, and most code in the kernel seems to just assume
    it won't happen, so it's probably safe to assume the same.

    --
    Robert Hancock Saskatoon, SK, Canada
    To email, remove "nospam" from hancockr@nospamshaw.ca
    Home Page: http://www.roberthancock.com/

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