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

From: Yijing Wang
Date: Fri Nov 21 2014 - 07:12:51 EST

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
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.


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).



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