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: <47659BF3.4040100@zytor.com>
Date:	Sun, 16 Dec 2007 13:43:15 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Pavel Machek <pavel@....cz>, "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>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
 on some AMD64x2 laptops, etc.

Ingo Molnar wrote:
> * H. Peter Anvin <hpa@...or.com> wrote:
> 
>> Pavel Machek wrote:
>>>> this is also something for v2.6.24 merging.
>>> As much as I like this patch, I do not think it is suitable for
>>> .24. Too risky, I'd say.
>>>
>> No kidding!  We're talking about removing a hack that has been 
>> successful on thousands of pieces of hardware over 15 years because it 
>                                                              ^----[*]
>> breaks ONE machine.
> 
> [*] "- none of which needs it anymore -"
> 
> there, fixed it for you ;-)
> 
> So lets keep this in perspective: this is a hack that only helps on a 
> very low number of systems. (the PIT of one PII era chipset is known to 
> be affected)

Yes, but the status quo has been *tested* on thousands of systems and is 
known to work.  Thus, changing it puts things into unknown territory, 
even if only a small number of machines actually need the current 
configuration.

Heck, there are only a small number of 386/486 machines still in 
operation and being actively updated.

> unfortunately this hack's side-effects are mis-used by an unknown number 
> of drivers to mask PCI posting bugs. We want to figure out those bugs 
> (safely and carefully) and we want to remove this hack from modern 
> machines that dont need it. Doing anything else would be superstition.
> 
> anyway, we likely wont be doing anything about this in .24.

Again, 24 is "right out".  25 is a "maybe", IMO.  Rene's fix could be an 
exception, since it is a DMI-keyed workaround for a specific machine and 
doesn't change behaviour in general.

	-hpa
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