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

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Date:	Mon, 17 Dec 2007 22:47:37 +0100
From:	Rene Herman <rene.herman@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Rene Herman <rene.herman@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.com>,
	"H. Peter Anvin" <hpa@...or.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 17-12-07 22:41, Ingo Molnar wrote:
> * Rene Herman <rene.herman@...il.com> wrote:
> 
>> On 17-12-07 17:12, Alan Cox wrote:
>>
>>> I don't think we should be offering udelay based delays at this point.
>>> There are a lot of drivers to fix first. This is just one trivial example
>> I agree. This thread's too full of people calling this outb method a 
>> dumb hack. It's a well-known legacy PC thing and while in practice the 
>> udelay might be a functional replacement for a majority of cases (save 
>> the races you are finding) a delay proportional to the bus speed makes 
>> great sense certainly when talking to hardware that itself runs 
>> proportinal to the bus speed for example.
>>
>> So, really, how about just sticking in this minimal version for now? 
>> Only switches the port to 0xed based on DMI and is all that is needed 
>> to fix the actual problem. This should be minimal and no-risk enough 
>> that it could also go to .24 if people want it to. It'll fix a few HP 
>> laptops (I'll try and get/verify the dv6000z DMI strings as well).
>>
>> Ingo?
>>
>> Signed-off-by: Rene Herman <rene.herman@...il.com>
> 
> hm, i see this as a step backwards from the pretty flexible patch that 
> David already tested. (and which also passed a few hundred bootup tests 
> on my x86 test-grid)

Please see Alan's comment that udelay (and none) shouldn't yet be provided 
as a choice. It opens race windows in drivers even when it works in practice 
on most setups. The version with "udelay" and "none" is not minimal, not low 
risk and certainly not .24 material.

David tested this part of the patch just as well.

Attached again (with the boot param) since I see I left in an extraneous 
'Use the" in the kernel-parameters.txt file.

Rene.

View attachment "dmi-port80-minimal-bootparam.diff" of type "text/plain" (10709 bytes)