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Re: [Qemu-devel] [PATCH 00/13] iommu series

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 00/13] iommu series
Date: Wed, 20 Jun 2012 16:12:42 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

On 06/19/2012 01:39 AM, Benjamin Herrenschmidt wrote:
This is a rebase of the iommu series and the barrier patch together
on top of current qemu.

As for our discussions about doing things with Memory Regions etc
I eventually came to the conclusion that we should just apply this
first :-)

My reasons (other than it makes my life much easier which it does)
are that:

This series sucks pretty bad. I don't think it can be a lot better though without major rearchitecting so I'm in favor of applying this now and dealing with the fall-out later.

I'll respond in detail where all of the problems are. I don't have easy solutions to offer though.


Anthony Liguori

  - We already have PCI DMA accessors, so devices using those
will be unaffected by further changes

  - The few devices that are modified in this series to use the
DMA accessors directly are ... few, and need to do it essentially
because they either deal with multiple bus types (AHCI, EHCI,...)
or because they are in a separate layer (bdev). Fixing them to
use some other interfaces would be easy (they are few)) and might
be unnecessary as well as we might want (or can) easily keep an
object of type "DMAContext" to represent the DMA capabilities of a
device as the head of the chain of MemoryRegions in a future
more flexible design.

  - It provides a good spot to stick our memory barrier

  - It gives us something working now for 1.2, I know that at least
freescale powerpc and a number of ARM folks are waiting for it.


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