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SubjectRe: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in
On Sat, Jan 12, 2008 at 09:45:57AM -0800, Arjan van de Ven wrote:
> btw this is my main objection to your patch; it intertwines the conf1
> and mmconfig code even more.

There is nothing wrong with it; please realize that mmconf and conf1 are
just different cpu-side interfaces. Both produce precisely the *same* bus
cycles as far as the lower 256-byte space is concerned.

> When (and I'm saying "when" not "if") systems arrive that only have
> MMCONFIG for some of the devices, we'll have to detangle this again,
> and I'm really not looking forward to that.

MMCONFIG for *some* of the devices? This doesn't sound realistic
from technical point of view.
MMCONFIG-only systems? Sure. I really hope to see these. But it won't
be PC-AT architecture anymore. It has to be something like alpha,
for instance, fully utilizing the 64-bit address space, and we'll have
to have the whole low-level PCI infrastructure completely different
for these future platforms anyway.
Right now, each and every x86 chipset *does* require working
conf1 just in order to set up the mmconf aperture. It's the very
fundamental thing, sort of design philosophy.

Ivan.


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