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Re: lwl-lwr

To: Ralf Baechle <>
Subject: Re: lwl-lwr
From: Alan Cox <>
Date: 21 May 2003 13:49:45 +0100
Cc: "Kevin D. Kissell" <>, Gilad Benjamini <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <025401c31f03$0e993370$10eca8c0@grendel> <>
On Mer, 2003-05-21 at 01:34, Ralf Baechle wrote:
> > 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 

This would seem the sane approach. 

> 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 ...

They would need to grant a license for general GPL use, the GPL itself
does not intend to allow other restrictions that would make the code non
free. There are a billion examples of prior art for software fixing up
of exceptions and software emulation of alignment fixups however.

Maybe MIPS can clarify their position officially.

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