On Wednesday, November 9, 2016 1:54:53 PM CET One Thousand Gnomes wrote:

quoted

I think it is a relatively safe assumption that there is only one
ISA bridge. A lot of old drivers hardcode PIO or memory addresses

It's not a safe assumption for x86 at least. There are a few systems with
multiple ISA busses particularly older laptops with a docking station.

But do they have multiple ISA domains? There is no real harm in supporting
it, the (small) downsides I can think of are:

- a few extra cycles for the lookup, from possibly walking a linked list
  to find the correct set of helpers and MMIO addresses
- making it too general could invite more people to design hardware
  around the infrastructure when we really want them to stop adding
  stuff like this.

	Arnd