Re: Removal of bus->msi assignment breaks MSI with stacked domains

From: Thomas Gleixner
Date: Fri Nov 21 2014 - 05:49:20 EST


On Fri, 21 Nov 2014, Marc Zyngier wrote:
> On 21/11/14 01:46, Thomas Gleixner wrote:
> > So the real question is:
> >
> > What is the association level requirement to properly identify the
> > irqdomain for a specific device on any given architecture with and
> > without IOMMU, interrupt redirection etc.
> >
> > To be honest: I don't know.
> >
> > My gut feeling tells me that it's at the device level, but I really
> > leave that decision to the experts in that field.
> Given the above requirement (single device associated to DMAR), I can
> see two possibilities:
> - we represent DMAR as a single PCI bus: feels a bit artificial
> - we move the MSI domain to the device, as you suggested.
> The second one seems a lot more attractive to me.

And that's very useful if you want to support MSI on non PCI

> Also, it is not clear to me what is the advantage of getting rid of the
> MSI controller. By doing so, we loose an important part of the topology
> information (the irq domain is another level of abstraction).

That was probably my misunderstanding of the msi controller. I had the
impression it's just there to expose the MSI properties of a device,
i.e. a magic wrapper which can be replaced by the MSI irqdomain work.

If that handles other information as well, then it's probably a
misnomer to begin with.



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