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

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Date:	Tue, 8 Jan 2008 13:51:47 +0100 (CET)
From:	Bodo Eggert <7eggert@....de>
To:	Rene Herman <rene.herman@...access.nl>
cc:	"H. Peter Anvin" <hpa@...or.com>, Bodo Eggert <7eggert@....de>,
	Christer Weinigel <christer@...nigel.se>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.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: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

On Tue, 8 Jan 2008, Rene Herman wrote:
> On 08-01-08 00:24, H. Peter Anvin wrote:
> > Rene Herman wrote:

> > > Is this only about the ones then left for things like legacy PIC and PIT?
> > > Does anyone care about just sticking in a udelay(2) (or 1) there as a
> > > replacement and call it a day?
> > > 
> > 
> > PIT is problematic because the PIT may be necessary for udelay setup.
> 
> Yes, can initialise loops_per_jiffy conservatively. Just didn't quite get why
> you guys are talking about an ISA bus speed parameter.

If the ISA bus is below 8 MHz, we might need a longer delay. If we default
to the longer delay, the delay will be too long for more than 99,99 % of 
all systems, not counting i586+. Especially if the driver is fine-tuned to 
give maximum throughput, this may be bad.

OTOH, the DOS drivers I heared about use delays and would break on 
underclocked ISA busses if the n * ISA_HZ delay was needed. Maybe
somebody having a configurable ISA bus speed and some problematic
chips can test it ...

-- 
Fun things to slip into your budget
"I [Meow Cat] sliped in 'Legal fees for firing Jim (Jim's my [his] boss).'
Jim approved the budget and was fired when upper management saw the budget."
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