linux-kernel - Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

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Message-ID: <475DE6F4.80702@zytor.com>
Date:	Mon, 10 Dec 2007 17:25:08 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Newall <david@...idnewall.com>
CC:	Krzysztof Halasa <khc@...waw.pl>,
	Rene Herman <rene.herman@...access.nl>,
	Pavel Machek <pavel@....cz>, Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

David Newall wrote:
> Where did the 8us delay come from?  The documentation and source is 
> careful not to say how long the delay is.  Would changing it to, say 
> 1us, be technically wrong?  Is code that requires 8us correct?

I think a single ISA bus transaction is 1 µs, so two of them back to 
back should be 2 µs, not 8 µs...

	-hpa
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