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

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Date:	Fri, 21 Nov 2014 09:54:40 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	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>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Will Deacon <will.deacon@....com>,
	"Catalin Marinas" <catalin.marinas@....com>
Subject: Re: Removal of bus->msi assignment breaks MSI with stacked domains

>> 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;	
}

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
> 
> .
> 


-- 
Thanks!
Yijing

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