linux-kernel - Re: fpu IO port reservation (arch/i386)

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Date:	21 Sep 2007 18:22:12 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Peter Fordham <peter.fordham@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: fpu IO port reservation (arch/i386)

"Maciej W. Rozycki" <macro@...ux-mips.org> writes:

> Hi Peter,
> 
> > Does anybody know why we reserve this range of IO ports for 'fpu'?
> > AFAIK from all the IO maps I can find on the internet for various x86
> > chipsets only 0x00f0 is actaully ever used.
> 
>  There are two ports used: 0xf0 is the busy latch reset and 0xf1 is the 
> coprocessor reset.  They are legacy ports resulting from the interesting 
> way the FPU has been wired by IBM in their PC design. 

Was it really needed on 386s? I didn't think there was a IBM 386 PC.

> None of them is 
> used by Linux for i486 and newer systems, which can support the FPU in its 
> native configuration.

I can remove it from x86-64 at least. 

-Andi
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