linux-kernel - Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on some AMD64x2 laptops, etc.

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Date:	Fri, 14 Dec 2007 10:02:57 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"David P. Reed" <dpreed@...d.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Rene Herman <rene.herman@...access.nl>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
 on some AMD64x2 laptops, etc.

Ingo Molnar wrote:
> 
> wow, cool fix! (I remember that there were other systems as well that 
> are affected by port 0x80 muckery - i thought we had removed port 0x80 
> accesses long ago.)
> 
> how about the simpler fix below, as a first-level approach? We can then 
> remove the _p in/out sequences after this.
> 

I believe this will suffer from the issue that was raised: this will use 
udelay() long before loop calibration (and no, we can't just "be 
conservative" since there is no "conservative" value we can use.)

Worse, I suspect that at least the PIT, which may need to be used for 
udelay calibration, is one of the devices that may be affected.  I have 
seen the Verilog for a contemporary chipset, and it can only access the 
PIT once per microsecond -- this actually has to do with the definition 
of the PIT; some of the PIT operations are ill-defined if allowed at a 
higher frequency than the PIT clock.

	-hpa
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