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Re: [Qemu-devel] [RFC] QOMification of AXI stream

From: Anthony Liguori
Subject: Re: [Qemu-devel] [RFC] QOMification of AXI stream
Date: Mon, 11 Jun 2012 10:03:56 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

On 06/11/2012 09:53 AM, Peter Maydell wrote:
On 11 June 2012 15:38, Edgar E. Iglesias<address@hidden>  wrote:
On Mon, Jun 11, 2012 at 02:39:56PM +0100, Peter Maydell wrote:
Ideally the interface used by DMA controllers should be identical to
the interface used by CPUs to talk to the rest of the system: it's
exactly the same bus interface in hardware, after all.

I thought we were talking about the interface between the DMA ctrl
and the I/O (devices). Not between the DMA and the "memory" bus system.

In hardware (at least for AXI) they're the same thing. A DMA
controller is a bus master, just like a CPU. They don't care
whether the slave is RAM or a device, they're just issuing
memory transactions to addresses.

It looks like the AXI stream interface also includes a word array. I can't tell though whether this is just a decomposed scatter/gather list though.

There doesn't appear to be a notion of an address though. You could make all operations go to address 0 though but it makes me wonder if that's stretching the concept of DMA a bit too much.


Anthony Liguori

-- PMM

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