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pci host bridge address assignment question

Discussion in 'Embedded' started by John Black, Oct 5, 2004.

  1. John Black

    John Black Guest

    I am trying to figure out for a PCI host bridge how the address
    assignment is generated, and I have this question.

    Let's say the host uses some other bus, bus foo, as the primary bus,
    then use foo_to_pci as PCI host bridge to connect PCI world. Then in
    assigning the system address map, the host may pre-allocate a big chunk
    of IO and memory space to PCI. Let's just say the PCI memory space is
    [0xA0000000:0xFFFFFFFF] and PCI IO space is [0x90000000:0x9FFFFFFF].

    Then the PCI init code in system bootup should assign all the PCI
    device address map, IO and memory, to these 2 ranges respectively.

    So far it sounds all natural. But in reading some Linux document it
    mentions that PCI IO address "always" starts at 0x0. Is it real? The
    foo_to_pci bridge does have address alias functionality, then do I have
    to alias IO space from [0x90000000:0x9FFFFFFF] to [0x0:0x0FFFFFFF]?

    John Black, Oct 5, 2004
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