Date: Tue, 8 Jan 2008 14:37:02 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "David P. Reed" <dpreed@reed.com>
Cc: Bodo Eggert <7eggert@gmx.de>, Rene Herman <rene.herman@keyaccess.nl>,
       "H. Peter Anvin" <hpa@zytor.com>,
       Christer Weinigel <christer@weinigel.se>, Ingo Molnar <mingo@elte.hu>,
       Paul Rolland <rol@as2917.net>, Pavel Machek <pavel@ucw.cz>,
       Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@redhat.com>, rol@witbe.net
Subject: Re: [linux-kernel] Re: [PATCH] x86: provide a DMI based port 0x80
 I/O delay override.
Message-ID: <20080108143702.5569c7bf@lxorguk.ukuu.org.uk>
In-Reply-To: <478375AA.3090306@reed.com>
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> 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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