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[Xen-devel] RE: [PATCH 2/4 v2] PCI: support ARI capability

To: "Roland Dreier" <rdreier@xxxxxxxxx>, "Alex Chiang" <achiang@xxxxxx>
Subject: [Xen-devel] RE: [PATCH 2/4 v2] PCI: support ARI capability
From: "Zhao, Yu" <yu.zhao@xxxxxxxxx>
Date: Wed, 10 Sep 2008 15:48:04 +0800
Cc: Randy Dunlap <randy.dunlap@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Grant Grundler <grundler@xxxxxxxxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Matthew Wilcox <matthew@xxxxxx>, linux-pci@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Greg KH <greg@xxxxxxxxx>
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Thread-topic: [PATCH 2/4 v2] PCI: support ARI capability
On Monday, September 01, 2008 11:50 PM, Roland Dreier wrote:
>To: Alex Chiang
>Cc: Zhao, Yu; Jesse Barnes; linux-pci@xxxxxxxxxxxxxxx; Randy Dunlap; Greg KH;
>Grant Grundler; Matthew Wilcox; linux-kernel@xxxxxxxxxxxxxxx;
>kvm@xxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx;
>Subject: Re: [PATCH 2/4 v2] PCI: support ARI capability
> > > +config PCI_ARI
> > > + bool "PCI ARI support"
> > > + depends on PCI
> > > + default n
> > > + help
> > > +   This enables PCI Alternative Routing-ID Interpretation.
> >
> > This Kconfig help text is a little weak. Why not include the text
> > you've already written here:
> >
> >     Support Alternative Routing-ID Interpretation (ARI), which
> >     increases the number of functions that can be supported by a PCIe
> >     endpoint. ARI is required by SR-IOV.
>I agree with this improvement to the help text.  But a further question
>is whether ARI even merits its own user-visible config option.  Is it
>worth having yet another choice for users?  When would someone want ARI
>but not SR-IOV?

ARI is an independent PCI Express extended capability. Multi-function devices 
supporting this capability may use it to track dependency between different 
functions and assign function group numbers to these functions.

Another reason to keep this separated with SR-IOV is that after ARI is enabled, 
PCI Express Endpoint may have non-zero slot number (device number), which is 
different from traditional PCI Express Endpoint.


> - R.

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