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Re: [Qemu-devel] [PATCH 01/10] Add stub functions for PCI device models

From: Eduard - Gabriel Munteanu
Subject: Re: [Qemu-devel] [PATCH 01/10] Add stub functions for PCI device models to do PCI DMA
Date: Sat, 3 Sep 2011 06:04:26 +0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Fri, Sep 02, 2011 at 11:37:25AM +0300, Avi Kivity wrote:
> On 09/01/2011 07:05 PM, Anthony Liguori wrote:
> >
> > The challenge is what you do about something like ne2k where the core 
> > chipset can either be a PCI device or an ISA device.  You would have 
> > to implement a wrapper around pci_dma_rw() in order to turn it into 
> > cpu_physical_memory_rw when doing ISA.
> btw, ISA DMA is very different, no?  You program a dma controller to 
> copy memory from the device to RAM (or vice versa); the device never 
> initiates a transaction IIRC.

It seems to me ISA devices should use memory I/O primitives exposed by
the ISA bus code. Or maybe the DMA controllers involved should be doing
that. As for either-PCI/ISA devices, they can handle dispatching DMA
through the right interface themselves.

Anyway, I'm not sure why we're worrying about this now. Do we even have
IOMMUs for such use cases?


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