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Re: Proposal: non-PC ISA bus support

To: Richard Henderson <>
Subject: Re: Proposal: non-PC ISA bus support
From: Geert Uytterhoeven <>
Date: Thu, 22 Jun 2000 11:15:31 +0200 (MET DST)
Cc: Linux kernel <>, Linux/PPC Development <>, Linux/MIPS Development <>
In-reply-to: <>
On Thu, 22 Jun 2000, Richard Henderson wrote:

> On Thu, Jun 22, 2000 at 09:41:58AM +0200, Geert Uytterhoeven wrote:
> > The problem is that drivers assume ISA memory space is at 0 and use e.g.
> > 
> >     request_mem_region(0xa0000, 65536)
> >     
> > to request the legacy VGA region, while it should be
> > 
> >     request_mem_region(isa_mem_base+0xa0000, 65536)
> > 
> > for compatibility with anything besides ia32.
> Well, yes and no.  Again, what I'm saying is that one way
> to handle this is to *pretend* isa_mem_base==0, and that
> the entire ISA region is contiguous.  Certainly that's good
> enough for region allocations.  And if the damage is undone
> by ioremap, then the effect is not visible.

That works only if there's nothing else at address 0 that keeps the resource

> I'm not disagreeing that it would make sense to make this
> all a bit more explicit with proper interfaces.  However,
> I don't see that happening any time real soon.

Hence my proposal for isa_request_mem_region(). It allows platform specific
code to take care of both the base address and the sparsity (if needed).

> > > What does your bus configuration look like?
> > 
> > There are multiple legacy ISA regions on some PowerMacs, which
> > have multiple PCI buses and such.
> I guessed that.  I was hoping to get specifics.

Benjamin Herrenschmidt <> can tell you more about it.



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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