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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Message-ID: <20071215074358.GD12110@elte.hu>
Date:	Sat, 15 Dec 2007 08:43:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
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.


* H. Peter Anvin <hpa@...or.com> wrote:

> 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.

i think the native_io_delay() in quirks.c signals the obvious solution: 
a DMI (or otherwise) driven quirk that activates a port 0x80 based delay 
on such boards. Combined with an iodelay=port80 boot option as well 
perhaps, just in case someone hits a system that is not blacklisted yet. 
This way such crazy broken hardware can be mapped correctly - like we 
map such quirks in every other case. Perhaps even do this workaround on 
the PIT driver level. Instead of perpetuating the superstition of port 
80 forever.

	Ingo
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