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Re: lwl-lwr

To: Ralf Baechle <>
Subject: Re: lwl-lwr
From: "Maciej W. Rozycki" <>
Date: Wed, 21 May 2003 11:56:44 +0200 (MET DST)
Cc: "Kevin D. Kissell" <>, Gilad Benjamini <>,
In-reply-to: <>
Organization: Technical University of Gdansk
Original-recipient: rfc822;
On Wed, 21 May 2003, Ralf Baechle wrote:

> > There's really no such thing as "disabling" lwl/lwr.  They are part 
> > of the base MIPS instruction set.  If one wants to live without them, 
> > one can either rig a compiler to emit multi-instruction sequences instead 
> > of lwr/lwl to do the appropriate shifts and masks (which is slower on all 
> > targets), or you can rig the OS to emulate them, and hope that the 
> > processors 
> > lacking support will take clean reserved instruction traps, where the 
> > function 
> > can be emulated (which is "free" for code running  on CPUs with lwl/lwr, 
> > but *really* slow for the guys doing emulation).
> Technically you're right ...  In reality lwl/lwr are covered by US patent
> 4,814,976 which would also cover a software implementation.  So unless MIPS
> grants a license for the purpose of emulation in the Linux kernel ...

 For practical reasons I believe it can be dealt with without patent
infringing, but I am not that excited with doing anything at all about it. 

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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