Re: [PATCH 02/04] PCI: use the MCFG table to properly access pci devices (i386)

[Andi Kleen <ak@suse.de>]

On Wed, Jun 15, 2005 at 10:54:47AM -0700, Greg KH wrote:
> On Wed, Jun 15, 2005 at 11:48:33AM +0200, Andi Kleen wrote:
> > On Tue, Jun 14, 2005 at 10:31:20PM -0700, Greg KH wrote:
> > > Now that we have access to the whole MCFG table, let's properly use it
> > > for all pci device accesses (as that's what it is there for, some boxes
> > > don't put all the busses into one entry.)
> > > 
> > > If, for some reason, the table is incorrect, we fallback to the "old
> > > style" of mmconfig accesses, namely, we just assume the first entry in
> > > the table is the one for us, and blindly use it.
> > 
> > I think it would be better to set different bus->ops at probe
> > time, not walk the table at runtime.
> 
> Yeah, I thought of that, but it's the same ops pointers that we want to
> have called for the different devices.  The only thing different is the
> base address of the bus.

There can be bus segments that don't support it at all and still
need the old port based access method
(e.g. on a AMD K8 box the busses of the internal northbridge need this) 

For those you would have bus->ops pointing to the old port code,
for the others to the mmconfig code.

That's the whole point of the patch btw - to support mmconfig even
on these machines ;-) 

> 
> In sleeping on it, I thought about just using the void * we have
> availble for the bus to use to hold this base address, that way we only
> have to look it up at bus creation time, not for every device access.
> 
> Of course to do that I might need another callback in the ops structure,
> but hey, what's one more pointer :)
> 
> Sound a bit more reasonable?  I'll try to prototype this later tonight.

Yes, caching the base address would be a good idea too.

-Andi