linux-kernel - Re: [PATCH 6/6] ARM: dts: Add pcie controller node for Samsung EXYNOS5440 SoC

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Date:	Fri, 7 Jun 2013 10:20:50 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Jingoo Han <jg1.han@...sung.com>,
	'Thomas Petazzoni' <thomas.petazzoni@...e-electrons.com>,
	linux-samsung-soc@...r.kernel.org,
	'Siva Reddy Kallam' <siva.kallam@...sung.com>,
	'Surendranath Gurivireddy Balla' <suren.reddy@...sung.com>,
	linux-pci@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	'Thierry Reding' <thierry.reding@...onic-design.de>,
	linux-kernel@...r.kernel.org,
	'Grant Likely' <grant.likely@...retlab.ca>,
	'Kukjin Kim' <kgene.kim@...sung.com>,
	'Thomas Abraham' <thomas.abraham@...aro.org>,
	'Bjorn Helgaas' <bhelgaas@...gle.com>,
	'Andrew Murray' <andrew.murray@....com>
Subject: Re: [PATCH 6/6] ARM: dts: Add pcie controller node for Samsung
 EXYNOS5440 SoC

On Fri, Jun 07, 2013 at 01:59:43PM +0200, Arnd Bergmann wrote:
> On Friday 07 June 2013 18:19:40 Jingoo Han wrote:
> > Hi Jason Gunthorpe,
> > 
> > I implemented 'Single domain' with Exynos PCIe for last two months;
> > however, it cannot work properly due to the hardware restriction.
> > Each MEM region is hard-wired.
> > 
> > Thus, I will send Exynos PCIe V3 patch as 'Separate domains'.
> 
> Yes, I think that is best, if the hardware is clearly designed as
> separate domains, this is what we should do by default in the
> driver. For the Marvell case with its 10 separate ports, much
> more address space would be wasted by having one domain per
> port and that hardware let us work around it by remapping the
> physical address space windows. For Exynos there is much less to
> lose and I too cannot see how it would be done in the first
> place.

Sounds fair to me.

But when we talk about multiple domains we don't mean a disjoint range
bus bus numbers, as your other email shows:

00:00.0 PCI bridge: Samsung Electronics Co Ltd Device a549 (rev 01) (prog-if 00 [Normal decode])
10:00.0 PCI bridge: Samsung Electronics Co Ltd Device a549 (rev 01) (prog-if 00 [Normal decode])

We mean multiple domains, it should look like this:

0000:00:00.0 PCI bridge: Samsung Electronics Co Ltd Device a549 (rev 01) (prog-if 00 [Normal decode])
0001:00:00.0 PCI bridge: Samsung Electronics Co Ltd Device a549 (rev 01) (prog-if 00 [Normal decode])

ie lspci -D.

Each domain gets a unique bus number range, config space, io range,
etc. This is much clearer to everyone than trying to pretend there is
only one domain when the HW is actually multi-domain.

Jason
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