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From: Paul Brook <paul@codesourcery.com>
Date: Fri, 8 Jun 2012 14:53:03 +0100
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Subject: Re: [Qemu-devel] [RFC] QOMification of AXI stream
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: Michal Simek <monstr@monstr.eu>, "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, Peter Crosthwaite <peter.crosthwaite@petalogix.com>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Andreas =?iso-8859-1?q?F=E4rber?= <afaerber@suse.de>, John Williams <john.williams@petalogix.com>

> >> So what im proposing is AXI stream is implemented as a unidirectional
> >> point to point bus. The xilinx ethernet system would consist of two of
> >> these buses one for tx, one for rx.
> > 
> > I thought the idea was that with QOM the bus/device model would go away.
> > The DMA controller implements an AXIDMA interface, and the device has a
> > AXIDMA link that's connected to that interface.
> > 
> > Of course we then hit the usual problem with QOM that we can only link to
> > objects, and it's impossible to expose multiple interfaces of the same
> > type.
> 
> No, QOM supports multiple inheritance of interfaces so you absolutely can
> inherit from multiple different interfaces.

But you can't have multiple instances of the same interface.  And the 
interfaces must be stateless.  Hence you need the proxy object.

Paul