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

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Message-ID: <546EA2AB.9080609@linux.intel.com>
Date:	Fri, 21 Nov 2014 10:25:47 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Yijing Wang <wangyijing@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Marc Zyngier <marc.zyngier@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: Removal of bus->msi assignment breaks MSI with stacked domains

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?
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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