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

From: Yijing Wang
Date: Thu Nov 20 2014 - 22:46:46 EST

On 2014/11/21 10:25, Jiang Liu wrote:
> On 2014/11/21 9:54, Yijing Wang wrote:
>>>> Thomas, let me know if you want to do that. I suppose we could add a new
>>>> patch to add it back, but that would leave bisection broken for the
>>>> interval between c167caf8d174 and the patch that adds it back.
>>> Fortunately my irq/irqdomain branch is not immutable yet. So we have
>>> no problem at that point. I can rebase on your branch until tomorrow
>>> night. Or just rebase on mainline and we sort out the merge conflicts
>>> later, i.e. delegate them to Linus so his job of pulling stuff gets
>>> not completely boring.
>> Hi Thomas, sorry for my introducing the broken.
>>> What I'm more worried about is whether this intended change is going
>>> to inflict a problem on Jiangs intention to deduce the MSI irq domain
>>> from the device, which we really need for making DMAR work w/o going
>>> through loops and hoops.
>>> I have limited knowledge about the actual scope of iommu (DMAR) units
>>> versus device/bus/host-controllers, so I would appreciate a proper
>>> explanation for that from you or Jiang or both.
>> In my personal opinion, if it's not necessary, we should not put stuff
>> into pci_dev or pci_bus. If we plan to save msi_controller in pci_bus or
>> pci_dev.
>> I have a proposal, I would be appreciated if you could give some comments.
>> First we refactor pci_host_bridge to make a generic
>> pci_host_bridge, then we could save pci domain in it to eliminate
>> arch specific functions. I aslo wanted to save msi_controller as
>> pci domain, but now Jiang refactor hierarchy irq domain, and
>> pci devices under the same pci host bridge may need to associate
>> to different msi_controllers.
>> So I want to associate a msi_controller finding ops with generic pci_host_bridge,
>> then every pci device could find its msi_controller/irq_domain by a
>> common function
>> E.g
>> struct msi_controller *pci_msi_controller(struct pci_dev *pdev)
>> {
>> struct msi_controller *ctrl;
>> struct pci_host_bridge *host = find_pci_host_bridge(pdev->bus);
>> if (host && host->pci_get_msi_controller)
>> ctrl = pci_host_bridge->pci_get_msi_controller(struct pci_dev *pdev);
>> return ctrl;
>> }
> Hi Yijing,
> This may be a little overhead for x86 because we could get
> irqdomain from pci_dev itself through:
> pci_dev->dev.archdata.iommu->ir_msi_domain.
> This doesn't work currently because pci_dev->dev.archdata.iommu
> is set on the first dma mapping request, but we have a plan to set it
> when creating PCI devices so we don't need to search the iommu list
> at runtime.
> Even the whole msi_controller concept may be killed for x86.
> Actually I'm trying to convert all MSI arch code to use hierarchy
> irqdomain, then we don't need arch_setup_msi_irqs() and
> msi_controller.setup_irq() and related anymore. But the issue is
> that it affects too many architectures and may cause slightly code
> size increase.
> If we could convert all PCI MSI code to use hierarchy irqdomain,
> then the suggested interface is:
> struct irq_domain *pci_get_msi_irqdomain(struct pci_dev *pdev);
> Thoughts?

So the final solution depends the MSI refactoring work progress.
(glue layer)
I prefer pci_dev->msi_controller->(msi irq hierarchy domain)/(normal msi irq allocation code).
If we want to eliminate msi_controller, we must force all PCI MSI code to use hierarchy
irq domain. I doubt whether it is worth to do.


> Regards!
> Gerry
>> If I miss something, please let me know, thanks.
>> Thanks!
>> Yijing.
>>> My guts feeling tells me that anything less granular than the bus
>>> level is wrong and according to my limited knowledge Intel even has
>>> DMARs which are assigned to a single device it's even more wrong. So
>>> the proper change would be not to push it from bus to something above
>>> the bus, but instead make it a per device property.
>>> But my knowledge there is limited, so I rely on the PCI/architecture
>>> experts to sort that out.
>>> Let me know ASAP.
>>> Thanks,
>>> tglx
>>> .
> .


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