Re: fpu IO port reservation (arch/i386)

From: Andi Kleen
Date: Fri Sep 21 2007 - 12:22:22 EST


"Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx> 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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/