linux-kernel - Re: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

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Date:	Fri, 11 Jan 2008 09:35:57 -0500
From:	"David P. Reed" <dpreed@...d.com>
To:	Rene Herman <rene.herman@...access.nl>
CC:	Zachary Amsden <zach@...are.com>, "H. Peter Anvin" <hpa@...or.com>,
	Christer Weinigel <christer@...nigel.se>,
	Ondrej Zary <linux@...nbow-software.org>,
	Bodo Eggert <7eggert@....de>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Paul Rolland <rol@...917.net>, Pavel Machek <pavel@....cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	rol <rol@...be.net>
Subject: Re: Re: [PATCH] x86: provide a DMI based port 0x80
 I/O delay override.



Rene Herman wrote:
> On 11-01-08 02:36, Zachary Amsden wrote:
>
>> FWIW, I fixed the problem locally by recompiling, changing port 80 to 
>> port 84 in io.h; works great, and doesn't conflict with any occupied 
>> ports.
>
> Might not give you a "proper" delay though. 0xed should be a better 
> choice...
>
I don't think there is any magic here.  I modified the patch to do *no 
delay at all* in the io_delay "quirk" and have been running reliably for 
weeks including the very heavy I/O load that comes from using software 
RAID on this nice laptop that has two separate SATA drives!  This 
particular laptop has no problematic devices - the only problem is 
actually in the CMOS_READ and CMOS_WRITE macros that *use* the _p 
operations in a way that is unnecessary on this machine.  (in fact, it 
would be hard to add a problematic device - there's no PCMCIA slot 
either, and so every option is USB or Firewire).

Using 0xED happens to work, but it's not guaranteed to work either.  
There is not a "standard" for an "unused port that is mapped to cause a 
bus abort on the LPC bus".   More problematic is that I would think some 
people might want to turn on the AMD feature that generates machine 
checks if a bus timeout happens.   The whole point of machine checks is 
to allow the machine to be more reliable.   Using any "unused port" for 
a delay means that the machine check feature is wasted and utterly unusable.


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