linux-kernel - Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS

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Message-ID: <20100426142546.2e77b1ba@virtuousgeek.org>
Date:	Mon, 26 Apr 2010 14:25:46 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Bjorn Helgaas" <bjorn.helgaas@...com>,
	"Andy Isaacson" <adi@...apodia.org>,
	"R. Andrew Bailey" <bailey@...mai.com>,
	"Yinghai" <yinghai.lu@...cle.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, guenter.roeck@...csson.com,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Thomas Renninger" <trenn@...e.de>, yaneti@...lera.com
Subject: Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below 
 BIOS_END

On Mon, 26 Apr 2010 14:12:35 -0700
"H. Peter Anvin" <hpa@...or.com> wrote:

> > On Mon, 26 Apr 2010 14:27:56 -0600
> > Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> >> I'm a little concerned that those patches are a sledgehammer approach.
> >> Previously, IORESOURCE_BUSY has basically been used for mutual exclusion
> >> between drivers that would otherwise claim the same resource.  It hasn't
> >> been used to guide resource assignment in the PCI/PNP/etc core.  Maybe
> >> it's a good idea to also use IORESOURCE_BUSY there, but I'm not sure.
> >> Right now it feels like undesirable overloading to me.
> >
> > I guess that's true, removing those regions from the pool entirely
> > might be better?  Or some other, clear way of expressing that the
> > regions aren't available to drivers.  Maybe we need a new IO resource
> > type for platform ranges.
> >
> >> I think it also leads to at least one problem: Guenter's machine has no
> >> VGA but has a PCI device that lives at 0xa0000.  The driver for that
> >> device won't be able to request that region if the arch code has marked
> >> it busy.
> >
> > Ah good point, so we'll want another approach at any rate.  Yinghai?
> 
> What we need is to keep track of the areas available for address space
> allocation by dynamically addressed devices, as distinct from address
> space that is in use by a kernel-known device.  There is an in-between,
> which one can call "here there be dragons" space, which should never be
> used for dynamic device allocation, but if a platform device or
> pre-assigned device uses that space then it should be allowed to be
> allocated.
> 
> In the case of x86, anything that is E820_RESERVED, *or* in the legacy
> region (below 1 MB) and is not RAM, is "here there be dragons" space.

Agreed.  The trickier part is handling any platform devices that
request_resource against that space.  But maybe we don't need to do
anything special; just making sure we avoid it in the PCI "BIOS" code
as Bjorn did may be sufficient.

-- 
Jesse Barnes, Intel Open Source Technology Center
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