[openib-general] Help with CONFIG_PCI_MSI in the kernel

[Roland Dreier]

    Jason> Just as a preface, I whipped this patch up because I have a
    Jason> Asus with a broken BIOS and I wanted to test with MSI-X on
    Jason> IB cards. It needs a little more thought before being
    Jason> merged, but the method seemed relevent given the discussion
    Jason> on Fedora disabling MSI.

This patch probably is a good thing to work around buggy BIOSes.  But
I don't think it helps Fedora at all.  The issue (as I understand it)
is not that some devices try to use MSI and don't work, but that some
systems completely fail to boot because of the (non-MSI) IRQ changes
that CONFIG_PCI_MSI also (confusingly) enables.

To put it naively, what breaks things is all interrupt handling stuff
that changes /proc/interrupts from

 17:       4797          0   IO-APIC-level  eth0

to

177:    1942286          0   IO-APIC-level  eth0

_That's_ the stuff you have to fix everywhere to get Fedora to enable MSI.

 - R.