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    SubjectRe: [sodaville] [PATCH 03/11] x86/dtb: Add a device tree for CE4100
    On 11/29/2010 03:42 PM, Alan Cox wrote:
    >> The usual layout is that the PCI bus is a direct child of
    >> the root node, and the ISA bus is a child of the PCI bus.
    >> That reflects the "Northbridge + Southbridge" wiring that
    >
    > That isn't strictly true either. On many PC devices the ISA bus (or LPC
    > bus nowdays) has no heirarchy as such because ISA cycles get issued if
    > the PCI cycles don't generate a response. In addition some cycles go to
    > both busses on some chipsets and there are various bits of magic so the
    > I/O spaces and particularly the memory spaces are intertwined.
    >
    > So it's not a subordinate bus really, its a bit weirder. PCMCIA is
    > probably a sub-bus when you've got a PCI/PCMCIA adapter but ISA in
    > general is a bit fuzzy.
    >

    Actually, it can go both ways -- there are ISA/LPC busses which are true
    childs of PCI busses -- in particular, are subject to the decoding
    restrictions of the host bridge -- and there are those that aren't
    logically even if they are physically. The reason for this is that
    subtractive decoding can be done either at the back end (as in a classic
    PCI/ISA system with a single PCI bus) or at the front end (as in
    HyperTransport for example.)

    -hpa


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