linux-kernel - Re: PCI: MSI interrupts masked using prohibited method

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Message-ID: <20080722155629.1160635e@brian.englab.brq.redhat.com>
Date:	Tue, 22 Jul 2008 15:56:29 +0200
From:	Michal Schmidt <mschmidt@...hat.com>
To:	David Vrabel <david.vrabel@....com>
Cc:	Matthew Wilcox <matthew@....cx>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: PCI: MSI interrupts masked using prohibited method

On Fri, 18 Jul 2008 11:33:10 +0100
David Vrabel <david.vrabel@....com> wrote:

> Matthew Wilcox wrote:
> > 
> > I think David's original patch (just declining to mask the
> > interrupt) is the best approach to take.  Perhaps architectures
> > with saner interrupt hardware would like to try the approach I've
> > mentioned here.
> > 
> > I don't like the comment in http://lkml.org/lkml/2008/6/27/199 as
> > it's not prohibited ... just a bad idea.  How about this patch?
> 
> The PCI specification is quite clear that it's prohibited.  The
> problem also is more severe than simply having spurious interrupts --
> with some devices if a line interrupt is generated (regardless of
> whether it ends up on the bus) then no more interrupts are generated.
> 
> I also think that the change requires a comment in the code.  It odd
> to have a mask function that doesn't really mask so a comment is
> necessary to explain why this is.
> 
> Please apply this instead.
> 
> David

This breaks the setting of SMP affinity for MSI interrupts :-(
With the patch, writes to /proc/irq/<n>/smp_affinity are ignored for an
MSI interrupt.

Michal
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