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

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Date:	Mon, 29 Sep 2014 17:08:49 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
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, Sep 29, 2014 at 4:31 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> 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().

Agreed.  It's obvious that we can't apply Liviu's patch as-is.

> 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.

There's definitely a lot of work here if we ever want to make this happen.

Bjorn
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