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

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Message-Id: <1199902644.7369.355.camel@bodhitayantram.eng.vmware.com>
Date:	Wed, 09 Jan 2008 10:17:24 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Christer Weinigel <christer@...nigel.se>,
	"David P. Reed" <dpreed@...d.com>, Avi Kivity <avi@...ranet.com>,
	Ondrej Zary <linux@...nbow-software.org>,
	"H. Peter Anvin" <hpa@...or.com>, Bodo Eggert <7eggert@....de>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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 <rol@...be.net>
Subject: Re: Re: [PATCH] x86: provide a DMI based port 0x80
	I/O delay override.

On Wed, 2008-01-09 at 16:27 +0100, Rene Herman wrote:
> On 09-01-08 06:30, Christer Weinigel wrote:
> I'd not expect very time crtical. The current outb_p use gives a delay 
> somewhere between .5 and 2 microseconds as per earlier survey meaning a 
> udelay(1) or 2 would be enough -- again, at the point that udelay() is sensible.
> 
> New machines don't use the legacy PIC anymore anyway.
> 
> > The floppy controller code uses outb_p.  Even though there might be
> > floppy controllers on modern systems, I'd rather leave the floppy code
> > alone since it's supposed to be very fragile.  If you still use
> > floppies you deserve what you get.
> 
> Floppies forever. In practice, leaving it alone isn't going to matter, but 
> in that same practice changing it to udelay() probably doesn't either. The 
> ones to leave alone are the ones that are clumsy/impossible to test and the 
> ones such as in NIC drivers that were specifically tuned.

I'm speaking specifically in terms of 64-bit platforms here.  Shouldn't
we unconditionally drop outb_p doing extra port I/O on 64-bit
architectures?  Especially considering they don't even have an ISA bus
where the decode timing could even matter?

> If simple outb_p() deprecation is considered enough instead, no need to 
> touch anything in drivers/, only changes to "outb(); udelay()" outside drivers/.
> 
> I'd let Alan decide here.

Agree.

Zach

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