Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS_END

[jacob pan]

H. Peter Anvin Mon, 26 Apr 2010 14:12:35 -0700
>> On Mon, 26 Apr 2010 14:27:56 -0600
>> Bjorn Helgaas <bjorn.helgaas@xxxxxx> 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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