linux-kernel - Re: [PATCH] arm64: Add architecture support for PCI

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Message-ID: <4118142.2mQ5BlBdTZ@wuerfel>
Date:	Tue, 04 Feb 2014 20:21:38 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	linux-pci <linux-pci@...r.kernel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: Add architecture support for PCI

On Tuesday 04 February 2014 12:10:55 Jason Gunthorpe wrote:
> 
> For instance to support peer-to-peer IO you need to have a consisent,
> non-overlapping set of bus/device/function/tag to uniquely route TLPs
> within the chip. Cross domain TLP routing in HW is non-trivial.

Yes, that is a good reason.

> IOMMUs (and SR-IOv) rely on the BDF to identify the originating device
> for each TLP. Multiple domains means a much more complex IOMMU
> environment.

I fear we already have to support complex IOMMU setups on ARM,
whether there are multiple PCI domains or not. But it would be
nice in theory not to require it.

> Failure to integrate on-chip devices into the PCI world also means
> thing like SR-IOv won't work sanely with on-chip devices.

I'd consider this a feature ;)

But you are probably right: people will do SR-IOV whether we like
it or not, and they will try to do it on non-PCI devices too,
and great suffering will be involved.

	Arnd
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