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    SubjectRe: Exposing ROM's though sysfs
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    > So you can do port I/O on low addresses but not memory accesses? For some
    > cards simply throwing away reads and writes to the low memory area is
    > probably ok since it'll just be doing things like printing a BIOS banner or a
    > pretty logo. But then again, I've never disassembled one so I can't be sure.
    > Alan would probably know though :)

    Yes, typically, on Apple north bridges, you have the PIO space memory
    mapped somewhere in the CPU address space, generating IO cycles from 0
    to N (usually 16Mb), but the MMIO space is directly mapped 1:1 from
    0x8000000.

    > If you can't do legacy port I/O on a given bus though, I think you'd be out of
    > luck wrt POSTing a card with an x86 BIOS.

    Port IO should be fine in most cases (there might be one or 2 weird cases
    with earlier models, but overall, it's fine). The typical case is a machine
    using Apple "UniNorth" chipset (the one that supports AGP, been out for a while
    now), since the AGP slot and the PCI bus are on 2 separate domains. Both can
    do Port IO at any low address, but they are completely separate domains.

    All this could be very nicely dealt with by the kernel driver.

    Ben.


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