Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device

[Anthony Liguori]

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