is PCITAG big enough for future expansion?

[Benjamin Herrenschmidt]

On Wed, 2005-07-20 at 18:29 +0100, Alan Cox wrote:

> device + function is 8bits (8 functions, 32 slots)
> bus is 8bits
> 
> domain to X is a bit different to domain to the PCI space I suspect. A
> system can have multiple unconnected PCI busses that are not part of a
> domain (ie dont share config space)

The kernel exposes the domains nowadays, and devices on different
domains can have the same bus/devfn, so X should definitely use it. The
domain number itself does't really have a spec'd size. I think we expose
4 digits, thus 16 bits, in sysfs, but it's probably best for X to just
use an unsigned int there.
 
> I also don't know what the new PCI replacements do to all these values,
> and that may be more important ?

Yah... We have things like extended config space etc... coming along. I
don't know for sure what's going on with device+function, I _suppose_
they stay in the same range for now to be enough backward compatible,
but I'd rather see X on the safe side and use separate unsigned int's
instead.

Ben.