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    SubjectRe: PCI MSI breaks when booting with nosmp
    On Wednesday, April 23, 2008 11:23 am Jesse Barnes wrote:
    > On Wednesday, April 23, 2008 11:13 am Maciej W. Rozycki wrote:
    > > On Wed, 23 Apr 2008, Jesse Barnes wrote:
    > > > Yeah I think the patch is reasonable, would be good to get feedback
    > > > from Thomas/Andi/Ingo though...
    > >
    > > FWIW, the original idea behind "nosmp" or "maxcpus=0" (just as an
    > > implementation detail) vs "maxcpus=1" was that the two formers would
    > > disable the APIC circuitry altogether (including resisting from switching
    > > from the PIC compatibility mode on systems supporting it), while the
    > > latter would still boot UP, but with interrupts routed through the APICs.
    > > Essentially SMP implied all the MP circuitry/provisions in this context,
    > > the APICs being an inherent part of which. Therefore I think the
    > > original idea of implying "pci=nomsi" with "nosmp" certainly looks more
    > > in the spirit of the original setup to me.
    > >
    > > However we have "nolapic" these days as well and with this new proposal
    > > this option could effectively take over the old meaning of "nosmp" (you
    > > cannot do SMP without the local APIC, so "nolapic nosmp" is redundant).
    > > I am not entirely convinced it is the right way though...
    > Yeah, I'm not particularly attached to either meaning. It looks like we'll
    > setup the local apic on 32 bit if the NMI vector is a local apic one, so in
    > that case at least the behavior will be the same.
    > Anyway, we have two options:
    > 1) make nosmp/maxcpus=1 imply nolapic (and therefore disable MSI too)
    > 2) make nosmp enable the lapic (so MSI will work)

    Err, nosmp/maxcpus=0...

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