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

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Message-ID: <48807166.9010006@csr.com>
Date:	Fri, 18 Jul 2008 11:33:10 +0100
From:	David Vrabel <david.vrabel@....com>
To:	Matthew Wilcox <matthew@....cx>
CC:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PCI: MSI interrupts masked using prohibited method

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
-- 
David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park,  Tel: +44 (0)1223 692562
Cowley Road, Cambridge, CB4 0WZ                 http://www.csr.com/

View attachment "pci-dont-mask-msi-with-msi-enable-bit.patch" of type "text/x-diff" (2273 bytes)