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 14:42:26 +0100
From:	Rene Herman <rene.herman@...il.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>,
	"H. Peter Anvin" <hpa@...or.com>, 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.

On 14-12-07 14:15, 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.

Your version does the same thing that the version from Pavel/David does for 
32-bit at least.

> +/*
> + * Some legacy devices need delays for IN/OUT sequences. Most are
> + * probably not needed but it's the safest to just do this short delay:
> + */
> +void native_io_delay(void)
> +{
> +	udelay(1);
> +}

Also note the thread(s) on LKML where 2 us was decided to be a nicely 
conservative value:

http://lkml.org/lkml/2007/12/12/309

Also see: http://lkml.org/lkml/2007/12/14/72

And also: http://lkml.org/lkml/2007/12/12/221

As such, please wait a bit for a fuller resolution. We're still discussing this.

Rene.
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