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: <20071215132725.GA23166@elte.hu>
Date:	Sat, 15 Dec 2007 14:27:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rene Herman <rene.herman@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"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>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
	on some AMD64x2 laptops, etc.


* Rene Herman <rene.herman@...il.com> wrote:

> The issue is -- how do you safely replace the outb pre-loops_per_jiffy 
> calibration? I'm currently running with the attached hack (not 
> submitted, only for 32-bit and discussion) the idea of which might be 
> the best we can do?

how about doing a known-NOP chipset cycle? For example:

  inb(PIC_SLAVE_IMR)

? I.e. instead of trying to find an unused port, lets try to find a 
known-used platform register that has no side-effects if read. Use it 
unconditionally during early bootup and change it to an udelay after 
calibration. (or use it after early bootup too if a boot parameter has 
been specified) Or something like this.

	Ingo
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