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

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Date:	Fri, 21 Nov 2014 10:05:36 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.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>,
	"H. Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	"David Woodhouse" <dwmw2@...radead.org>
Subject: Re: Removal of bus->msi assignment breaks MSI with stacked domains

On 2014/11/21 9:46, 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.

I choose the pci_host_bridge to place the .get_msi_ctrl() ops, because
I think how to associate pci_dev and msi_controller is platform specific,
and we could initialize pci_host_bridge in platform pci host drivers to
avoid call platform specific functions when we scan or setup a pci device.

Thanks!
Yijing.

> 
> Thanks,
> 
> 	tglx
> 
> .
> 


-- 
Thanks!
Yijing

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