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From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Andi Kleen <andi@firstfloor.org>
Subject: Re: PCI MSI breaks when booting with nosmp
Date: Mon, 21 Apr 2008 12:06:59 -0700
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Cc: linux-pci@atrey.karlin.mff.cuni.cz, Jean Delvare <jdelvare@suse.de>,
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On Monday, April 21, 2008 11:45 am Andi Kleen wrote:
> Jesse Barnes <jbarnes@virtuousgeek.org> writes:
> > Ok, I see this too on my desktop machine.  It looks like we're not
> > getting interrupts setup correctly in the nosmp case.  Still digging
> > through to see why though...
>
> NoSMP disables the io-apic and a lot of modern systems don't work without
> APIC.
>
> If you just want to run with a single cpu for testing etc. always use
> maxcpus=1 (not 0, that will disable the APIC too)

Right...  but it looks like the MSI code is buggy when noapic is specified via 
nosmp or maxcpus=0.  We should either fix it to work with noapic or disable 
it like we do the ioapic when nosmp or maxcpus=0:

index 99ce949..a0cd0ab 100644
--- a/init/main.c
+++ b/init/main.c
@@ -148,6 +148,7 @@ static int __init nosmp(char *str)
 {
        setup_max_cpus = 0;
        disable_ioapic_setup();
+       pci_no_msi();
        return 0;
 }

@@ -156,9 +157,10 @@ early_param("nosmp", nosmp);
 static int __init maxcpus(char *str)
 {
        get_option(&str, &setup_max_cpus);
-       if (setup_max_cpus == 0)
+       if (setup_max_cpus == 0) {
                disable_ioapic_setup();
-
+               pci_no_msi();
+       }
        return 0;
 }