linux-kernel - Re: PCI MSI breaks when booting with nosmp

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Message-Id: <200804231132.19874.jbarnes@virtuousgeek.org>
Date:	Wed, 23 Apr 2008 11:32:18 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Jean Delvare <jdelvare@...e.de>, Andi Kleen <andi@...stfloor.org>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Tejun Heo <htejun@...il.com>,
	Tom Long Nguyen <tom.l.nguyen@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Jeff Garzik <jgarzik@...ox.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 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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