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Re: Proposal: non-PC ISA bus support

To: Benjamin Herrenschmidt <>
Subject: Re: Proposal: non-PC ISA bus support
From: Geert Uytterhoeven <>
Date: Tue, 20 Jun 2000 14:41:34 +0200 (MET DST)
Cc: Linux/PPC Development <>, Linux/MIPS Development <>, Linux kernel <>
In-reply-to: <>
On Tue, 20 Jun 2000, Benjamin Herrenschmidt wrote:
> On Tue, Jun 20, 2000, Geert Uytterhoeven <>
> wrote:
> > 1. Provide /proc/bus/isa/map, which contains the ISA I/O and memory space
> >    mappings on machines where these are memory mapped.
> >
> >    Example (on PPC CHRP LongTrail):
> >
> >     callisto$ cat /proc/bus/isa/map
> >     f8000000        01000000        IO
> >     f7000000        01000000        MEM
> >     callisto$
> Looks fine except for one thing: How can we handle weird HW (like Apple
> Uni-N bridge) that has actually 3 different IO spaces at different
> locations (all of them beeing childs of the same PCI bus).

AFAIK this is a violation of the PCI spec. But of course that doesn't help you

> This is more or less related since the ISA iospace can be considered as a
> subset of the PCI IO space. The problem is generic (it happens with both
> "pure" PCI drivers doing IOs and ISA drivers doing IOs). The problem
> exist for both the kernel and userland apps like XFree wanting to do PCI
> or ISA IOs. The kernel has a built-in IO-base, your patch would expose it
> to userland fixing part of the problem for XFree (so userland don't have
> to probe for zillion different bridges) but wouldn't solve the problem of
> multiple busses.
> Paul suggested mapping them one after each other in a single contiguous
> region (with the appropriate fixup in the kernel PCI io resources) but
> this can work only for PCI IOs (drivers using the io resource base).
> Drivers hard-coding legacy IO addresses will still not work (except if
> they are on the first bus).

Concatenating the I/O spaces seems like the best solution to me as well.

> We still can decide (and that's what I currently do in the kernel) that
> IO space is only supported on one of those 3 busses (the one on which the
> external PCI is). This prevents however use of IOs on the AGP slot, which
> is a problem for things like XFree who may try to use VGA addresses on
> the card.

> I still don't have a clue about a good solution to this issue. Apple
> solves it in their kernel by having an object oriented bus structure,
> each device asking for mappings to their parent bridge, based on the
> device tree and independently of PCI bus numbers.

Hmmm... If you can live with only one video card with legacy support, what
about a kernel option to specify which of the 3 busses will be the first?

Else, we'll have to work around this in XFree86.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                                            -- Linus Torvalds

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