Date: Tue, 1 Jan 2008 18:32:38 +0100
From: Christer Weinigel <christer@weinigel.se>
To: Ingo Molnar <mingo@elte.hu>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, "David P. Reed" <dpreed@reed.com>,
       "H. Peter Anvin" <hpa@zytor.com>, Rene Herman <rene.herman@gmail.com>,
       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: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.
Message-ID: <20080101183238.74307174@weinigel.se>
In-Reply-To: <20080101164338.GA901@elte.hu>
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On Tue, 1 Jan 2008 17:43:38 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> if someone runs a fresh new kernel on an ancient device then timings 
> _will_ change a bit, no matter what we do. Alignments change, the 
> compiler output will change (old compilers get deprecated so a new 
> compiler might have to be picked), cache effects change - and this is 
> inevitable. The important thing is to not eliminate the delays - but
> we sure dont have to keep them cycle accurate (we couldnt even if we
> wanted to). The only way to get the _exact same_ behavior is to not
> change the kernel at all.

What I'm afraid is that udelay will be significantly slower, which
might hit anything that does a lot of gettimeofday calls (poking at the
PIT timer)  on embedded 386/486 systems.  On the other hand, those
systems might not want to upgrade to 2.6 anyway.  

And why do people keep buying HP hardware?  HP seem to be quite
Linux-unfriendly on the desktop [1] and on their laptops.  Apparently
HP doesn't even bother to try Linux on any of their non-server systems.

[1] Try running Linux on a HP DC7700 machine, there seems to be a lot
of magic stuff in those machines that doesn't work well with Linux.
They had some ACPI crap that stopped FC7 from booting without a lot of
magic PCI access options and audio still does not work.  

/Christer
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