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

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Message-Id: <200807221052.26879.jbarnes@virtuousgeek.org>
Date:	Tue, 22 Jul 2008 10:52:26 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Michal Schmidt <mschmidt@...hat.com>
Cc:	David Vrabel <david.vrabel@....com>,
	Matthew Wilcox <matthew@....cx>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: PCI: MSI interrupts masked using prohibited method

On Tuesday, July 22, 2008 6:56 am Michal Schmidt wrote:
> 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.

It should only break it for devices that don't provide a mask bit.  But given 
that we can't really mask generically on those devices, maybe that's ok given 
that it fixes the other problems mentioned in this thread...

Jesse
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