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

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Message-ID: <47783678.9070706@zytor.com>
Date:	Sun, 30 Dec 2007 16:23:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"David P. Reed" <dpreed@...d.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rene Herman <rene.herman@...access.nl>,
	Ingo Molnar <mingo@...e.hu>, Islam Amer <pharon@...il.com>,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

David P. Reed wrote:
> Alan Cox wrote:
>>> Now what's interesting is that the outb to port 80 is *faster* than 
>>> an outb to an unused port, on my machine.  So there's something there 
>>> - actually accepting the bus transaction.   In the ancient 5150 PC, 
>>> 80 was     
>>
>> Yes and I even told you a while back how to verify where it is. From the
>> timing you get its not on the LPC bus but chipset core so pretty
>> certainly an SMM trap as other systems with the same chipset don't have
>> the bug. Probably all that is needed is a BIOS upgrade
>>
>>   
> Actually, I could see whether it was SMM trapping due to AMD MSR's that 
> would allow such trapping, performance or debug registers.  Nothing was 
> set to trap with SMI or other traps on any port outputs.   But I'm 
> continuing to investigate for a cause.  It would be nice if it were a 
> BIOS-fixable problem.  It would be even nicer if the BIOS were GPL...

If it was an SMM trap, I would expect it to be trapped in the SuperIO chip.

	-hpa
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