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To: linux-kernel@vger.kernel.org
From: torvalds@transmeta.com (Linus Torvalds)
Subject: Re: [PATCH] Cleanup port 0x80 use (was: Re: IO delay ...)
Date: Fri, 15 Mar 2002 21:33:45 +0000 (UTC)
Organization: Transmeta Corporation
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In article <a6tm95$c55$1@cesium.transmeta.com>,
H. Peter Anvin <hpa@zytor.com> wrote:
>
>The ISA bus doesn't time out; a cycle on the ISA bus just happens, and
>the fact that noone is there to listen doesn't seem to matter.

The ISA bus doesn't time out, but the PCI access before it gets
forwarded to the ISA bus _does_, if the ISA bus is decoded using
nagative decoding.

This is why it's important that there not be a motherboard PCI device
that can decode the port - because if there is, the access is
potentially a much faster PCI-only decode.

Note that this really only matters on low-end machines anyway, as the
whole "inb_p()" thing tends to be used only for old ISA devices.  If you
have a new machine that is all PCI, I doubt that port 80h access matters
not at all. 

(Another way of saying it: if you have a machine with a PCI POST card,
none of this will matter)

			Linus
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