linux-kernel - Re: [PATCH] Disable i8042 checks on Intel Apple Macs

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Message-ID: <4B5A2B80.8040904@zytor.com>
Date:	Fri, 22 Jan 2010 14:49:36 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Robert Hancock <hancockrwd@...il.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bastien Nocera <hadess@...ess.net>,
	linux-kernel <linux-kernel@...r.kernel.org>, pjones@...hat.com,
	vojtech@...e.cz
Subject: Re: [PATCH] Disable i8042 checks on Intel Apple Macs

On 01/22/2010 02:33 PM, Robert Hancock wrote:
>>
>> You think it's reasonable to have the keyboard not work because
>> someone's KVM switch was in the wrong position when the system booted?
>> Sorry, that's not how the world works.  It's sad that someone had the
>> bright idea that things should work that way, but that is definitely a
>> regression I wouldn't want to deal with.
> 
> I don't imagine most KVM switches would result in this - they usually
> emulate the presence of a keyboard and mouse on all ports even if the
> input isn't the active one. It could be the reporter had an older
> switch that didn't do this.
> 

The good ones do.  The bad (cheap) ones just provide for a basic
electric disconnect.  Heck, there used to be mechanical KVMs...

> I expect that it's quite common for the BIOS to disable the controller
> if no device is detected, though. I think the idea is to prevent a
> useless device from showing up in Device Manager and free up resources
> for other devices. Problem is if it does this, we don't really know
> what it did other than remove the PNP entry, and whether using the
> controller anyway will work safely.
> 
> In any case, it's unlikely (though I admit I'm uncertain) that Windows
> is going to blindly probe for an 8042 controller if the PNP
> information doesn't indicate that one should be there - at least not
> if it's using the ACPI HAL. And for this sort of hardware
> compatibility issue, doing things differently than Windows does is
> ultimately asking for trouble in the long term. It's highly
> unreasonable to break that just for an unlikely corner case.

It's not unlikely - it's reality.  Furthermore, BIOS programmers do
weird things all the time, especially to support, say, old Windows
versions that noone cares about anymore but mattered then.

	-hpa
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