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: <20071211134725.GB17992@elf.ucw.cz>
Date:	Tue, 11 Dec 2007 14:47:25 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Newall <david@...idnewall.com>,
	"H. Peter Anvin" <hpa@...or.com>, Krzysztof Halasa <khc@...waw.pl>,
	Rene Herman <rene.herman@...access.nl>,
	"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 Tue 2007-12-11 14:32:49, Andi Kleen wrote:
> > The LPC bus behaviour is absolutely and precisely defined. The timing of
> > the inb is defined in bus clocks which is perfect as the devices needing
> > delay are running at a fraction of busclock usually busclock/2.
> > 
> > Older processors did not have a high precision timer so you couldn't
> > calibrate loop based delays for 1uS.
> 
> For newer CPUs udelay() would be probably fine though. We seem
> to have several documented examples now where the bus aborts
> trigger hardware bugs, and it is always better to avoid such situations.
> 
> I still think the best strategy would be to switch based on TSC
> availability. Perhaps move out*_p out of line to avoid code bloat.

Why is TSC significant? udelay() based on bogomips seems to be good
enough...?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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