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

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Message-ID: <4765D95C.4010404@zytor.com>
Date:	Sun, 16 Dec 2007 18:05:16 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rene Herman <rene.herman@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Paul Rolland <rol@...917.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>, "David P. Reed" <dpreed@...d.com>,
	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.

Rene Herman wrote:
> On 16-12-07 16:22, Ingo Molnar wrote:
> 
>> looks good to me. Could you please also provide three more controls 
>> that i suggested earlier:
>>
>>  - a boot option enabling/disabling the udelay based code
>>  - a .config method of enabling/disabling the udelay based code
>>  - a sysctl to toggle it
>>
>> if we want to clean this all up we'll need as many controls as possible.
> 
> This version does the boot and the .config option but not the sysctl. It 
> makes for clumsy code and I don't believe it provides for much added 
> value as soon as you have the boot option. I am moreover not completely 
> confident about things such as paravirt liking the possibility of the 
> native_io_delay being changed out from under them at unpredictable times.
> 

Incidentally, I had the thought earlier today that port 0xf0 might be a 
suitable delay port.  It is used only by the 387-emulating-a-287 hack 
for IRQ 13, which Linux doesn't use on 486+.

	-hpa
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