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To: "Manu Abraham" <abraham.manu@gmail.com>
Cc: "Leech, Christopher" <christopher.leech@intel.com>,
       "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@intel.com>,
       "Nelson, Shannon" <shannon.nelson@intel.com>, akpm@linux-foundation.org,
       linux-kernel@vger.kernel.org, davem@davemloft.net, jeff@garzik.org,
       "Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH 5/7] I/OAT: Add support for MSI and MSI-X
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From: Roland Dreier <rdreier@cisco.com>
Date: Fri, 20 Jul 2007 14:38:02 -0700
In-Reply-To: <1a297b360707201432q3dc976b3x214c2916ca235b6f@mail.gmail.com> (Manu Abraham's message of "Sat, 21 Jul 2007 01:32:36 +0400")
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 > In a case where you have a device that which supports MSI-X (multiple
 > interrupts) but the device in default is in MSI mode, ie some
 > configuration change is needed on the device. In such a case, how
 > would one handle between MSI-X and MSI ?
 > 
 > ie the device initially doesn't support MSI-X

I don't understand the question really.  Does the PCI spec even allow
a device to be in MSI mode by default?  Surely the OS must initialize
the address/message before the device can generate an MSI?

What device do you have in mind?  I guess the interesting case is a
PCIe device that supports MSI and MSI-X but not legacy interrupts.
However I would assume such a device would come up with both MSI and
MSI-X disabled.

 - R.