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

[Robert Hancock <hancockr@shaw.ca>]

Greg KH wrote:
> On Wed, Dec 19, 2007 at 05:17:46PM -0500, tcamuso@redhat.com 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
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