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Date: Mon, 12 Nov 2001 08:31:47 +0100 (MET)
From: Geert Uytterhoeven <geert@linux-m68k.org>
To: James Simmons <jsimmons@transvirtual.com>
cc: Bakonyi Ferenc <fero@sztalker.hu>,
        Linux Kernel Development <linux-kernel@vger.kernel.org>
Subject: Re: isa_* problems (hgafb is broken since 2.4.13)
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On Thu, 8 Nov 2001, James Simmons wrote:
> > I have two questions about asm-i386/io.h:
> > 1. Why #define __ISA_IO_base ((char *)(PAGE_OFFSET)) ?
> > 2. Why not #define __ISA_IO_base ((char *)0) ?
>
> For ix86 the ISA IO space start is at the very begining of memory. On
> other platforms like the PPC the ISA IO space is seperate from the
> regular memory space. It starts after the regular memory space thus the
> __ISA_IO_base will not be 0x0.

He's talking about asm-i386/io.h.

__ISA_IO_base (what's in a name, why not call it __ISA_MEM_base?!?!?) is the
kernel virtual address of the start of ISA _memory_ space. On ia32 PCs, ISA
memory space overlaps with the first 16 MB of real RAM, at CPU physical address
0.

(DISCLAIMER: my ia32 knowledge is limited)

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

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