Re: [PATCH 0/5]PCI: x86 MMCONFIG

[Robert Hancock]

Greg KH wrote:
> On Wed, Dec 19, 2007 at 05:17:46PM -0500, tcamuso@xxxxxxxxxx wrote:
> > OVERVIEW
> > =======
> >
> > The patches should be applied in sequence to obviate any
> > possible build problems.
> >
> > The patch-set was built against 2.6.24-rc5
> >
> > Description
> > ===========
> >
> > There exist devices that do not respond correctly to PCI
> > MMCONFIG accesses in x86 platforms.
>
> What devices are these?  Do you have reports of them somewhere?
>
> > This patch-set detects the problem by comparing an MMCONFIG
> > read to a Legacy PCI config read of the vendor/device dword
> > of every device discovered during the PCI probing sequence.
> >
> > A miscompare means that a device does not correctly respond
> > to MMCONFIG accesses. When the patch code detects this condition,
> > the bus that serves this device, and all subordinate buses, will
> > be programmed to use Legacy PCI Config accesses.
> >
> > This patch-set DOES NOT detect devices that generate machine
> > checks against MMCONFIG accesses. For such systems,
> > "pci=nommconf" is required in the boot command.
>
> That sounds like this patchset can cause bad side affects on hardware
> that currently works just fine.  That is not a good thing to be adding
> to the kernel, right?

I think we need more details on why this patch is needed. Also, we 
already have something like this in arch/x86/pci/mmconfig-shared.c, in 
the unreachable_devices function. This attempts to detect devices where 
MMCONFIG cannot access the configuration space (one of these would be at 
least one device in the AMD K8 built-in northbridge). If this is not 
sufficient, I would suggest expanding that mechanism instead of adding 
all this new code.

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@xxxxxxxxxxxxx
Home Page: http://www.roberthancock.com/

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