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

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Message-ID: <alpine.DEB.2.11.1411210233250.6439@nanos>
Date:	Fri, 21 Nov 2014 02:46:06 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yijing Wang <wangyijing@...wei.com>
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 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.

Thanks,

	tglx
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