Re: [RFC] PCI extended conf space when MMCONFIG disabled because of e820

[Arjan van de Ven <arjan@linux.intel.com>]

Rajesh Shah wrote:
> On Thu, Jun 22, 2006 at 12:32:19AM +0200, Andi Kleen wrote:
>> On Thursday 22 June 2006 00:19, Rajesh Shah wrote:
>>> On Wed, Jun 14, 2006 at 11:47:57PM -0700, Arjan van de Ven wrote:
>>>>> We need to improve this "mmconfig disabled" anyhow. Having the extended
>>>>> config space unavailable on lots of machines is also far from a viable
>>>>> solution :)
>>>> it's unlikely to be many machines though.
>>>>
>>> I just noticed today - this check killed PCI Express on 3 of the 4
>>> machines I normally use for testing.
>> What do you mean with killed PCI Express? PCI Express should
>> work even without extended config space, except error handling.
>>
> Yes, I meant it killed extended config space. Note that we are
> about to send out code that enables PCI Express error handling,
> so this will become more visible now.
> 
>> You're saying that you have lots of machines where the mmconfig
>> aperture is not fully reserved in e820?
>>
> Yes, I saw this in 3 out of 4 systems I checked. I'll go check
> some more systems too.
> 
>> Is it partially reserved (not for all busses) or not at all?
>>
> The MMCFG resources are not listed at all in the BIOS provided
> memory map.
> 
>> If someone does a patch to double check it against the ACPI name space
>> I'm not opposed to let it overrule the e820 heuristic.
>>
>> The point of this code is to pragmatically detect BIOS with obviously 
>> broken setups. It's not about standards lawyering.
>>
> Oh I agree with you that booting is more important. My point with
> the spec statement was that most BIOS developers may not even know
> they are doing something "wrong" by not listing these resources in
> the int15 E820 table, since the document they normally refer to
> doesn't say so. I suspect there are many more systems out there
> which do the same thing and will fail the check, but we never notice
> since most users don't try to ever access the extended space today.

well... it's sort of common sense though.. if you want non-ACPI OSes to 
work properly (like the older 2.4 based distros...)