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

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Date:	Mon, 26 Apr 2010 14:44:53 -0700
From:	jacob pan <jacob.jun.pan@...ux.intel.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below 
 BIOS_END

H. Peter Anvin Mon, 26 Apr 2010 14:12:35 -0700
>> 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.
>
>    -hpa
>
Moorestown has a similar situation where one of the PCI devices have a BAR
below 1MB. Moorestown also has the option not to have VGA.
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