linux-kernel - Re: [PATCH] PCI: Only enable IO window if supported

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Message-ID: <CAErSpo6AziA5GXEi6AizW2WP6oLVMd1p57pWunDNBQeVXxp1nw@mail.gmail.com>
Date:	Tue, 23 Jun 2015 18:02:14 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Guenter Roeck <linux@...ck-us.net>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH] PCI: Only enable IO window if supported

On Tue, Jun 23, 2015 at 5:46 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> On Tue, 2015-06-02 at 15:55 +0100, Lorenzo Pieralisi wrote:
>> While at it, do you think it is reasonable to also claim the bridge
>> windows (resources) in the respective pci_read_bridge_* calls ?
>
> No, don't claim in read. There's a clear distinction between gathering
> resources and claiming them, and we need to keep that.
>
> Some fixups might happen in between the two for example.

Are there any existing fixups like that?  Concrete examples would help
figure out the best way forward.

Most arches call pci_read_bridge_bases() from pcibios_fixup_bus().  I
think that's a poor place to do it because it's code that normally
doesn't have to be arch-specific.  Resource claiming is also usually
done from arch code, and it shouldn't be arch-specific either.

If we move both the read and claim into generic code, then we might
need to make sure there's a fixup phase in between or something.

Bjorn
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