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Re: Modpost warning on Alchemy

To: Sergei Shtylyov <>
Subject: Re: Modpost warning on Alchemy
From: "Maciej W. Rozycki" <>
Date: Wed, 1 Aug 2007 16:38:34 +0100 (BST)
Cc: Ralf Baechle <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <> <> <>
On Wed, 1 Aug 2007, Sergei Shtylyov wrote:

> > > Of course it will.  It shall work with whatever physical address space is
> > > supported by your MMU.  As long as the MMU is handled correctly that is,
> > > but I guess I may have omitted this clarification as obvious.
> >    Even on a CPU with 36-bit physical address? ;-)
>    WTF... I know I've typed "32-bit CPU"! :-/

 It does not matter.  The physical address of an I/O resource can be 
treated as a cookie that is converted, typically though an MMU, to another 
cookie that can be used with {read,write}{b,w,l}().  Of course you may 
have troubles ioremap()ping say 4GB of I/O space on a processor with a
32-bit virtual address space, but that is a corner case and typically your 
I/O space will be sparsely occupied.

 On a MIPS32 processor you have 512MB of KSEG0/1 unmapped virtual address 
space available for I/O devices located within the first 512MB of the 
physical address space plus 1GB of KSEG2 mapped virtual address space 
available for I/O devices located anywhere in the physical address space.  
That gives you from 1GB to 1.5GB of virtual address space for I/O which is 
enough for all the usual cases.


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