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Date: Mon, 28 Jan 2013 15:51:05 -0700
From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>,
	Arnd Bergmann <arnd@arndb.de>,
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	Shadi Ammouri <shadi@marvell.com>,
	Tawfik Bayouk <tawfik@marvell.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH v2 07/27] PCI: Add software-emulated host bridge
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On Mon, Jan 28, 2013 at 11:30:48PM +0100, Thomas Petazzoni wrote:
> Dear Jason Gunthorpe,
> 
> On Mon, 28 Jan 2013 15:23:48 -0700, Jason Gunthorpe wrote:
> 
> > I'm refering to your earlier question about what PCI IDs to use for
> > the SW emulated devices. If there is no need for the host bridge then
> > you only need 1 PCI ID (for the root port bridge) and you can probably
> > fairly safely re-use the one in the Marvell config space of the HW.
> 
> Ah, ok, I see. But isn't a host bridge needed to bind all the
> PCI-to-PCI bridges under a single bus, in order to get the global
> resource assignment I was referring to?

The PCI-E spec requires it, but AFAIK it doesn't actually *do*
anything on Linux, and Linux doesn't require it.

I thought Thierry did this experiment and decided it wasn't necessary:

> The reason is that with the latest bindings the matching of root
> ports to device tree nodes works as-is and nothing else indicates
> that the emulated host bridge is actually required to make any of
> this work. So in order not to introduce unneeded code I've left it
> out for now. If somebody decides that we actually need this host
> bridge (for standards compliance or whatnot) it could easily be
> added back.

Jason