linux-kernel - Re: [PATCH v8 6/9] pci: Introduce a domain number for pci_host

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Message-ID: <20140711160925.GD16321@arm.com>
Date:	Fri, 11 Jul 2014 17:09:25 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Liviu Dudau <Liviu.Dudau@....com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Arnd Bergmann <arnd@...db.de>,
	linaro-kernel <linaro-kernel@...ts.linaro.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>,
	LKML <linux-kernel@...r.kernel.org>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 6/9] pci: Introduce a domain number for
 pci_host_bridge.

On Fri, Jul 11, 2014 at 04:08:23PM +0100, Liviu Dudau wrote:
> On Fri, Jul 11, 2014 at 03:11:16PM +0100, Catalin Marinas wrote:
> > On Thu, Jul 10, 2014 at 11:36:10PM +0100, Bjorn Helgaas wrote:
> > > Most of the rest of the v7 discussion was about "Introduce a domain
> > > number for pci_host_bridge."  I think we should add arm64 using the
> > > existing pci_scan_root_bus() and keep the domain number in the arm64
> > > sysdata structure like every other arch does.  Isn't that feasible?
> > > We can worry about domain unification later.
> > 
> > I think that's what we were trying to avoid, adding an arm64-specific
> > pci_sys_data structure (and arm64-specific API). IIUC, avoiding this
> > would allow the host controller drivers to use the sysdata pointer for
> > their own private data structures.
> > 
> > Also since you can specify the domain number via DT (and in Liviu's
> > v8 patches read by of_create_pci_host_bridge), I think it would make
> > sense to have it stored in some generic data structures (e.g.
> > pci_host_bridge) rather than in an arm64 private sysdata.
> > 
> > (Liviu is thinking of an alternative API but maybe he could briefly
> > describe it here before posting a new series)
> 
> My plan is to keep the domain number in the pci_host_bridge and split
> the creation of the pci_host_bridge out of the pci_create_root_bus().

Wouldn't it make more sense to add domain_nr to the pci_bus structure
(well, only needed for the root bus)? It would simplify pci_domain_nr()
as well which only takes a pci_bus parameter.

> The new function (tentatively called pci_create_new_root_bus()) will
> no longer call pci_alloc_host_bridge() but will accept it as a
> parameter, allowing one to be able to set the domain_nr ahead of the
> root bus creation.

If we place domain_nr in pci_bus, this split wouldn't help but we still
need your original pci_create_root_bus_in_domain(). Are there other uses
of your proposal above?

Yet another alternative is to ignore PCI domains altogether (domain 0
always).

-- 
Catalin
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