Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in

Arjan van de Ven
2008-01-13T04:43:42Z

On Sat, 12 Jan 2008 20:36:59 -0500
Tony Camuso <tcamuso@redhat.com> wrote:

> Thanks, Arjan.
>
> The problem we have been experiencing has to do with Northbridges,
> not with devices.

correct for now.
HOWEVER, and this is the point Linus has made several times:
Just about NOBODY has devices that need the extended config space. At all.
So making this opt-in for devices allows our users to boot and use
their system if they are in the majority that has no need for even getting
close to this mess.

>
> As far as the device is concerned, after the Northbridge translates
> the config access into PCI bus cycles, the device has no idea what
> mechanism drove the Northbridge to the translation.

Wanne bet there'll be devices that screw this up? THere's devices that even screwed
up the 64-256 region after all.

> The patch I devised concerned itself with Northbridges and separated
> MMCONFIG-compliant buses from those that could not handle MMCONFIG.

THis kind of patchup has been going on for the better part of a year (well 2 years)
by now and it's STILL NOT ENOUGH, as you can see by the more patchups that have
been proposed as "alternative" to my approach.

>
> In my humble opinion, Port IO config access is here to stay, having
> been defined as an architected mechanism in the PCI 2.1 spec.
>
> This is most especially true for x86.
>
> In other words, for x86, I don't think we need to worry about Port
> IO config access ever going away at all.

You're wrong there. Sad to say, but you're wrong there.

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