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    SubjectRE: [PATCH 1/2] msi: Invert the sense of the MSI enables.
    Date

    > Hmm...

    > I find in section 6.1:
    > > In addition to PCI INTx compatible interrupt emulation, PCI Express
    > > requires support of MSI or MSI-X or both.

    > Which suggests that INTx support is required.

    Unfortunately, this can be equally well read to suggest that MSI/MSI-X is
    not required, but that MSI/MSI-x is required in addition if you choose to
    support PCI INTx. Section 6.1 is ambiguous and you have to look elsewhere to
    figure out if PCI INTx is required or not.

    I think the most natural reading of this is that if you choose to support
    PCI INTx compatible interrupt emulation, PCI Express requires support of MSI
    or MSI-X or both in addition.

    However, other sections are not ambiguous:

    "For legacy compatibility, PCI Express provides a PCI INTx emulation
    mechanism to signal
    interrupts to the system interrupt controller (typically part of the Root
    Complex). This
    mechanism is compatible with existing PCI software, and provides the same
    level and type
    service as corresponding PCI interrupt signaling mechanism and is
    independent of system
    interrupt controller specifics. This legacy compatibility mechanism allows
    boot device
    support without requiring complex BIOS-level interrupt configuration/control
    service stacks.
    It virtualizes PCI physical interrupt signals by using an in-band signaling
    mechanism."

    This seems to make it pretty clear that if a device requires MSI/MSI-X, it
    is broken. Devices are supposed to work even with PCI drivers that are not
    smart enough to support MSI/MSI-X.

    DS


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