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

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Date:	Tue, 8 Jan 2008 01:58:36 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"David P. Reed" <dpreed@...d.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Rene Herman <rene.herman@...access.nl>,
	Bodo Eggert <7eggert@....de>,
	Christer Weinigel <christer@...nigel.se>,
	Ingo Molnar <mingo@...e.hu>,
	Rene Herman <rene.herman@...il.com>,
	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@...be.net
Subject: Re: Re: [PATCH] x86: provide a DMI based port 0x80
 I/O delay override.

> The PIT usage for calibrating the delay loop can be moderated, if need 
> by, by using the PC BIOS which by definition uses the PIT correctly it 
> its int 15 function 83 call..   Just do it before coming up in a state 
> where the PC BIOS int 15h calls no longer work.  I gave code to do this 
> in a much earlier message.

And as I've said before we don't know if we have a PC BIOS. If we are
running from a kexec or on a Macintoy with EFI or an Xbox we may not.

As per previous discussions for the PIT we can simply guess a safe
initial udelay value and then tune the real one.

Alan
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