linux-kernel - Re: [PATCH v13 10/12] PCI: Assign unassigned bus resources in pci_scan_root

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Date:	Tue, 30 Sep 2014 08:31:52 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Liviu Dudau <Liviu.Dudau@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	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>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: Re: [PATCH v13 10/12] PCI: Assign unassigned bus resources in
 pci_scan_root_bus()

On Mon, 2014-09-29 at 15:33 -0600, Bjorn Helgaas wrote:
> > Right and on powerpc and others as well. We need to survey existing
> > resources. We also have a number of platform things that might need
> > to happen before we do the final re-assignment pass.
> 
> That's true today.  But I don't know whether it *has* to be this way
> forever.  On x86, pcibios_resource_survey() throws in E820 information
> (which we know long before we do any PCI enumeration) and some IO-APIC
> resources (it looks like we also know these before PCI enumeration).
> Powerpc has pcibios_reserve_legacy_regions(), but that looks like
> mostly stuff that could be done when we find the host bridge, before
> we enumerate PCI devices below it.

Oh we can probably change that but it's going to be much more work than
just moving the assignment into pci_scan_root_bus(). There are also a
number of subtle and not-so-subtle bits of code that rely on side
effects of the current code such as anything that tests for bus->added
or dev->added. Again, nothing we can't sort out eventually but the
transition might be a bit painful.

We might need to introduce a new flag for platforms converted to the
"new style" generalized resource assignment which we can deprecate once
everybody has moved over.

Cheers,
Ben.
 

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