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Re: [Xen-devel] [PATCH 2/3][RFC] MSI/MSI-X support fordom0/driver domain

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/3][RFC] MSI/MSI-X support fordom0/driver domain
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Mon, 28 May 2007 12:48:05 +0100
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On 28/5/07 12:33, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> I have the concern on xen to be involved in pirq allocation. Consider
> the current case where pirq == irq, for INTx type devices of dom0, the
> pirq number is always derived from ACPI table though static, and Xen
> doesn't know such static number before dom0 requests to bind. How
> about a MSI device enabled before an INTx only device? Also xen
> doesn't know the pirq number to be used in the future like hotplug
> case. 

Xen doesn't give a crap about the pirq namespace, except for subtle
semantics associated with legacy isa irqs 0-15. Or at least, what little
care it does have can (and likely will) be removed. So it's up to dom0
whether it wants its pirq namespace to correspond to BIOS-assigned scheme,
usual Linux allocation scheme, GSI space, or whatever. This interface will
let dom0 control how MSI and INTx is plumbed into its pirq space, if that's
what it wants. Other domUs will have no need for an association between
their pirq namespace and physical hardware/bios irq numbering -- in this
case it may make sense to leave it to Xen to do the allocation. But even
here, the interface as I described it would allow dom0 to have control over
domU allocation too if it wants it.

 -- Keir

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