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

[Yijing Wang]

å 2014/11/21 18:29, Marc Zyngier åé:
> Hi Thomas,
>
> On 21/11/14 01:46, Thomas Gleixner wrote:
> > On Fri, 21 Nov 2014, Yijing Wang wrote:
> > > On 2014/11/21 0:31, Marc Zyngier wrote:
> > > > Bjorn, Yijing,
> > > >
> > > > I've just realized that patch c167caf8d174 (PCI/MSI: Remove useless
> > > > bus->msi assignment) completely breaks MSI on arm64 when using the new
> > > > MSI stacked domain:
> > > Sorry, this is my first part to refactor MSI related code, now how
> > > to get pci msi_controller depends arch
> > > functions(pcibios_msi_controller() or arch_setup_msi_irq()), we are
> > > working on generic pci_host_bridge, after that, we could eventually
> > > eliminate MSI arch functions and find pci dev 's msi controller by
> > > pci_host_bridge->get_msi_controller().
> > The main question is why you think that pci_host_bridge is the proper
> > place to store that information.
> >
> > On x86 we have DMAR units associated to a single device. Each DMAR
> > unit is a seperate MSI irq domain.
> >
> > Can you guarantee that the pci_host_bridge is the right point to
> > provide the association of the device to the irq domain?
> >
> > 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. What I don't
> completely see is how the host bridge has all required the knowledge.

Hmmm, maybe I'm in the wrong direction,  I need to think more about it.

Thanks!
Yijing.


> 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).
>
> Thanks,
>
> 	M.

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