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Date: Mon, 19 Jul 2010 09:45:58 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg)
	device
References: <20100717095059.GA19767@amd.home.annexia.org>	<20100717095353.GB19767@amd.home.annexia.org>	<269D196D-8CE8-4E24-8EE1-39756AC55F7F@suse.de>	<20100718200942.GL13194@amd.home.annexia.org>	<44FD4F00-843D-41C8-B21A-148D16745015@suse.de>	<20100719062356.GU4689@redhat.com>	<20100719072802.GO13194@amd.home.annexia.org>
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To: Gleb Natapov <gleb@redhat.com>
Cc: qemu-devel@nongnu.org, "Richard W.M. Jones" <rjones@redhat.com>, Alexander Graf <agraf@suse.de>

On 07/19/2010 02:33 AM, Gleb Natapov wrote:
> On Mon, Jul 19, 2010 at 08:28:02AM +0100, Richard W.M. Jones wrote:
>    
>> On Mon, Jul 19, 2010 at 09:23:56AM +0300, Gleb Natapov wrote:
>>      
>>> That what I am warring about too. If we are adding device we have to be
>>> sure such device can actually exist on real hw too otherwise we may have
>>> problems later.
>>>        
>> I don't understand why the constraints of real h/w have anything to do
>> with this.  Can you explain?
>>
>>      
> Each time we do something not architectural it cause us troubles later.
> So constraints of real h/w is our constrains to.
>    

Your constraints are purely artificial.

There are plenty of places that something like fw_cfg could live and 
still do DMA.  It can directly hang off of the Southbridge.  It doesn't 
necessary need to be connected to the ISA/LPC buses.

Buses exist to multiplex I/O devices because of limited wiring space on 
motherboards.  There's no reason we need to constrain ourselves to 
minimize the number of virtual wires we emulate.

Regards,

Anthony Liguori