Re: [Qemu-devel] Machine description, an alternativ using XML

[Paul Brook <paul@codesourcery.com>]

>   <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.