From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Lcika-0000Ce-AX
	for qemu-devel@nongnu.org; Thu, 26 Feb 2009 11:06:16 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1LcikY-0000CC-Hp
	for qemu-devel@nongnu.org; Thu, 26 Feb 2009 11:06:15 -0500
Received: from [199.232.76.173] (port=43817 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1LcikY-0000C8-FK
	for qemu-devel@nongnu.org; Thu, 26 Feb 2009 11:06:14 -0500
Received: from mx20.gnu.org ([199.232.41.8]:26670)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <paul@codesourcery.com>)
	id 1LcikX-0006Rr-D9
	for qemu-devel@nongnu.org; Thu, 26 Feb 2009 11:06:14 -0500
Received: from mail.codesourcery.com ([65.74.133.4])
	by mx20.gnu.org with esmtp (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1LcikU-0004JP-NS
	for qemu-devel@nongnu.org; Thu, 26 Feb 2009 11:06:11 -0500
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Machine description, an alternativ using XML
Date: Thu, 26 Feb 2009 16:06:06 +0000
References: <004601c997de$50cbd7c0$f2638740$@tt@home.se>
In-Reply-To: <004601c997de$50cbd7c0$f2638740$@tt@home.se>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200902261606.06841.paul@codesourcery.com>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: =?iso-8859-1?q?Torbj=F6rn_Andersson?= <tobbe.tt@home.se>

>   <OBJECT name="pic" class="pl190">
>     <ATTRIBUTE name="pic">	<value obj_ref=":cpu"/>  </ATTRIBUTE>
>     <ATTRIBUTE name="memmap">	<value obj_ref=":memmap"/>  </ATTRIBUTE>
>     <ATTRIBUTE name="base">	<value integer="0xc0010000"/>  </ATTRIBUTE>
>   </OBJECT>
> <MACHINE/>

It looks like you're just using XML to encapsulate simple <key,value> pairs, 
which IMHO is completely the wrong way to use XML. Qemu already has to know 
about things like IO regions, IRQs, bus bindings. XML gives you the power to 
describe these things properly, rather than relying on clumsy naming 
conventions.

The current device implementations already know two much about this kind of 
detail. There's no reason[1] why every device needs to know how to map IO 
regions. They should just tell qemu what IO regions they have, and generic 
code will sort out the rest. Similarly for IRQs and bus bindings the device 
just registers that it provides particular functionality (IRQ source, I2c 
master/slave) and doesn't know or care how these are connected. PCI devices 
already have some of this abstraction, IMHO we need to go further (e.g. by 
removing the map_func callback), and extend this to other systems.

I think one of the most important goals of qemu machine description 
infrastructure is to abstract this kind of detail away from the devices.

Paul

[1] Ignoring the VGA hacks, which need to go way anyway.