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

[Brice Goglin <brice@myri.com>]

Arjan van de Ven wrote:
> Brice Goglin wrote:er.
>>
>> What would you think of a patch implementing the following strategy:
>> 1) if MMCONFIG works, always use it (no change)
>> 2) if MMCONFIG is disabled and we are accessing the regular config
>> space, use direct conf (no change, should ensure that any machine will
>> still boot fine)
>> 3) if MMCONFIG is disabled but we are accessing the _extended_ config
>> space, try mmconfig anyway since there's no other way to do it.
>
> an OS isn't allowed to mix old and new access methods realistically so
> I don't think
> this is a viable good solution...

Well, we are talking about using a different method to access the
extended config space only. This space is independent from the legacy
config space.
I don't see how mixing the old and new methods like this could lead to
any problem, we are not going to mix them to access the same registers.
But I agree with Andi about the possible dangerousness.

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 :) If you still do not like this first proposal, what do you
think of my other one ? (having chipset-specific checks in
pci_mmcfg_init to find out for sure whether mmconfig will work)

Thanks,
Brice