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

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Message-ID: <CAErSpo4+dGM4_FSk2BXq+QkC1s98CaFXm+zU_+zebnQNpoVBZA@mail.gmail.com>
Date:	Tue, 2 Jun 2015 11:32:23 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	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 2, 2015 at 9:55 AM, Lorenzo Pieralisi
<lorenzo.pieralisi@....com> wrote:
> On Wed, May 27, 2015 at 10:04:47PM +0100, Bjorn Helgaas wrote:

>> I really like the idea of pushing this into pci_read_bridge_io().
>>
>> I wonder if we can do the same with pci_read_bridge_mmio_pref(), and
>> somehow get rid of pci_bridge_check_ranges() altogether?
>>
>> I think I looked at doing that a while back, and it seems like there was
>> some wrinkle, but I don't remember what it was.
>
> While at it, do you think it is reasonable to also claim the bridge
> windows (resources) in the respective pci_read_bridge_* calls ?

I *do* think that's reasonable, and I think it would simplify some
things.  Of course, we can only claim them if firmware has already
programmed them.  If firmware hasn't done anything, the claim should
fail and we can treat it as an unassigned resource and allocate and
claim the space later.

I'm sure we'll trip over some issues when trying this, but it seems
like a logical thing to do, so I think it'd be great if you tried it
out.

Bjorn
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