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

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Message-ID: <20140711093007.GN6501@e106497-lin.cambridge.arm.com>
Date:	Fri, 11 Jul 2014 10:30:07 +0100
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci <linux-pci@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	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 Thu, Jul 10, 2014 at 11:36:10PM +0100, Bjorn Helgaas wrote:
> On Thu, Jul 10, 2014 at 3:47 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> 
> > I don't see a way out of adding new PCI interfaces if we want to have support in
> > the PCI framework for unifying existing architectures. Of course, there is the painful
> > alternative of changing the existing APIs and fixing arches in one go, but like you've
> > said is going to be messy. I don't think I (or the people and companies wanting PCIe
> > on arm64) should cop out and pick a quick fix that adds sysdata structure into arm64
> > just to avoid new APIs, as this is not going to help anyone in long term. What I can
> > do is to create a set of parallel APIs for pci_{scan,create}_root_bus() that take
> > a pci_host_bridge pointer and start converting architectures one by one to that API
> > while deprecating the existing one. That way we can add arm64 easily as it would be
> > the first architecture to use new code without breaking things *and* we provide a
> > migration path.
> 
> A lot of the v7 discussion was about pci_register_io_range().  I
> apologize, because I think I really derailed things there and it was
> unwarranted.  Arnd was right that migrating other arches should be a
> separate effort.  I *think* I was probably thinking about the proposal
> of adding pci_create_root_bus_in_domain(), and my reservations about
> that got transferred to the pci_register_io_range() discussion.  In
> any case, I'm completely fine with pci_register_io_range() now.
> 
> 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.

Thanks!

I'm really not that keen to add sysdata support in the arch code as it
requires initialisation code that I have tried to eliminate. What I'm
going to suggest for my v9 is a parallel set of APIs that arm64 will
be the first to use without changing the existing pci_{scan,create}_bus()
functions and then the conversion process will migrate arches to the new API.

Best regards,
Liviu

> 
> I haven't followed closely enough to know what other objections people had.
> 
> Bjorn
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

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