linux-kernel - Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI domain

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Date:	Wed, 10 Sep 2014 09:55:48 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Liviu Dudau <Liviu.Dudau@....com>,
	Rob Herring <robherring2@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	"Jason Gunthorpe" <jgunthorpe@...idianresearch.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Will Deacon" <Will.Deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci <linux-pci@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"Suravee Suthikulanit" <suravee.suthikulpanit@....com>,
	linux-arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Device Tree ML" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI
 domain_nr

>> OK. Sorry, I have one last question, because domain will be used to calculate the address used to
>> access PCI hardware config registers. So if DTS file doesn't report the domain, how do we know
>> we would access the right registers when we use the auto increment domain vaule ?
>> Has there a mechanism to make sure system can access the correct registers by the domain ?
> 
> I think you're referring to config access via ECAM (PCIe r3.0, sec
> 7.2.2).  In that case, I don't think the domain should be used to
> compute the memory-mapped configuration address.  Each host bridge is
> in exactly one domain, and each host bridge has an associated ECAM
> area base.  The address calculation uses the bus number, device
> number, function number, and register number to compute an offset into
> the ECAM area.
> 
> So as long as the DT tells you the ECAM information for each host
> bridge, that should be sufficient.  The domain number is then just a
> Linux convenience and is not tied to the platform as it is on ia64.

Hi Bjorn, you are right, thanks for your detailed explanation! :)

Thanks!
Yijing.

> 
> Bjorn
> 
> .
> 


-- 
Thanks!
Yijing

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