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: <475E341F.9000107@keyaccess.nl>
Date:	Tue, 11 Dec 2007 07:54:23 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	David Newall <david@...idnewall.com>,
	Krzysztof Halasa <khc@...waw.pl>, 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

On 11-12-07 02:25, H. Peter Anvin wrote:

> 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...

Sigh. And now where do these _two_ transactions come from? (and yes, see 
Alan's folowups, a transaction on a spec bus is 1 us).

Rene.
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