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

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Message-ID: <47659BAF.8030304@zytor.com>
Date:	Sun, 16 Dec 2007 13:42:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rene Herman <rene.herman@...il.com>
CC:	Paul Rolland <rol@...917.net>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...e.hu>,
	"David P. Reed" <dpreed@...d.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	rol@...be.net
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

Rene Herman wrote:
> 
> Well, I suppose. With stuff inline, constantly reloading dx also bloats 
> things up a bit but yes, out of line who cares. Do you think this 
> version is better?
> 

It probably comes down to which version is bigger (you probably also 
want to try uninlining.)

>> In the boot code, io_delay() is used to slow down accesses to the KBC, 
>> interrupt controller, INT13h logic, and the NMI gate, and to provide a 
>> fixed delay during A20 stabilization.
> 
> Thanks for the heads up (also saw the SMBIOS update to this) but those 
> don't seem to be a problem in fact. David Reed has been running with the 
> simple udelay(2) version of this and reported no more hangs. He moreover 
> reported no trouble after booting with "acpi=off" meaning that things 
> seem to be fine pre-acpi which the boot code (and this io_delay_init) 
> is. So I believe we get to ignore those.

Okay, so there is something inside ACPI which tickles this.  Which 
brings further credibility that it's activating a debugging hack, 
probably inside the SuperIO/system controller chip.

It would be interesting to know exactly which part of ACPI triggers 
this.  I bet it is a reference to system controller namespace.

	-hpa
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