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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [SOLUTION] "i8042.c: No controller found" -> OS sees
	no keyboard if I type "in BIOS"
Date: Mon, 8 Jun 2009 16:28:30 +0100
References: <4A0C232D.1020201@wpkg.org> <4A2D1C75.2040006@wpkg.org>
	<4A2D2743.4050501@redhat.com>
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To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>, Tomasz Chmielewski <mangoo@wpkg.org>, Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>

> > BTW, with "PS2_QUEUE_SIZE 16" I'm still able to trigger:
> >
> > i8042.c: No controller found.
> >
> >
> > Only with "PS2_QUEUE_SIZE 15" keyboard is detected every time I boot
> > the guest (unless that's what you meant by setting it to 16).
>
> I think this points to a bug in the bios.  The keyboard-internal queue
> size shouldn't cause any problems.

Either way, you're just papering over bugs in the bios/kernel.
My guess is that the bios is assuming it can drain the queue faster than 
external events can fill it back up. On real hardware this is often true (CPU 
and system bus speeds are many orders of magnitude greater than the keyboard 
serial line). However in a non cycle accurate simulator (like qemu) the 
keyboard events can happen infinitely fast. i.e. even with an internal queue 
size of 1 the bug will still trigger if sufficiently many PS2 events occur 
while the guest is draining the queue. 

Paul