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

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Message-ID: <20080108143702.5569c7bf@lxorguk.ukuu.org.uk>
Date:	Tue, 8 Jan 2008 14:37:02 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"David P. Reed" <dpreed@...d.com>
Cc:	Bodo Eggert <7eggert@....de>,
	Rene Herman <rene.herman@...access.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christer Weinigel <christer@...nigel.se>,
	Ingo Molnar <mingo@...e.hu>, 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 last time I heard of a 12 MHz bus in a PC system was in the days of 
> the PC-AT, when some clone makers sped up their buses (pre PCI!!!) in an 
> attempt to allow adapter card *memory* to run at the 12 MHz speed.

It wasn't about clone makers speeding up their busses. The ISA bus
originally ran at the CPU clock - 4.77/8/6/10 .. etc. Quite a few board
makers assumed 8MHz and while faster isn't a big problem at 8bit trying
to do the 8/16 bit decode with logic chips at 8MHz is quite tight and
above that generally broke. 8bit tends to work fine because you've got a
lot more timing headroom.

> I can't believe that we are not supporting today's machines correctly 
> because we are still trying to be compatible with a few (at most a 
> hundre thousand were manufactured!  Much less still functioning or 
> running Linux) machines.

It is about supporting this properly. Properly for ISA devices means
using I/O delays. Properly for chipset devices is probably using udelay.

> Now I understand that PC/104 machines and other things are very non PC 
> compatible, but are x86 processor architectures.  Do they even run x86 
> under 2.6.24?

Linux runs on x86, it isn't limited to PC type architectures at all. We
don't need a BIOS, we don't need legacy compatible I/O devices.

> for "relics" and develop a merged architecture called "modern machines" 
> to include only those PCs that have been made to work since, say, the 
> release of (cough) WIndows 2000?

No point. We've got the 64bit kernel for that. That is a much saner
boundary to throw out all the nutty stuff.

Alan
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