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SubjectRe: PCI MSI breaks when booting with nosmp
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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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