linux-mips
[Top] [All Lists]

Re: Proposal: non-PC ISA bus support

To: Richard Henderson <rth@twiddle.net>
Subject: Re: Proposal: non-PC ISA bus support
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 22 Jun 2000 11:15:31 +0200 (MET DST)
Cc: Linux kernel <linux-kernel@vger.rutgers.edu>, Linux/PPC Development <linuxppc-dev@lists.linuxppc.org>, Linux/MIPS Development <linux@cthulhu.engr.sgi.com>
In-reply-to: <20000622015903.A29666@twiddle.net>
Sender: owner-linux-mips@oss.sgi.com
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
busy.

> 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 <bh40@calva.net> can tell you more about it.

Gr{oetje,eeting}s,

                                                Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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


<Prev in Thread] Current Thread [Next in Thread>