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

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Date:	Sat, 8 Dec 2007 01:21:22 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Pavel Machek <pavel@....cz>
Cc:	"David P. Reed" <dpreed@...d.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

On Wed, Dec 05, 2007 at 11:10:39AM +0000, Pavel Machek wrote:
> On Fri 2007-12-07 09:50:26, David P. Reed wrote:
> > My machine in question, for example, needs no waiting 
> > within CMOS_READs at all.   And I doubt any other 
> > chip/device needs waiting that isn't already provided by 
> > the bus. the i/o to port 80 is very, very odd in this 
> > context.  Actually, modern machines have potentially 
> > more serious problems with i/o ops to non-existent 
> > addresses, which may cause real bus wierdness.
> 
> I dislike outb_p clobbering port 0x80, but you are wrong here. BIOSes
> already do outs to port 0x80 for debugging reason, so these accesses
> are unlikely to do something bad.

They only do that briefly during boot though. But Linux
can do it much more often. If it's a race
or similar it might just not trigger with the BIOS.

-Andi
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