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Re: [Qemu-devel] [PATCH 1/8] rc4030: create custom DMA address space

From: Hervé Poussineau
Subject: Re: [Qemu-devel] [PATCH 1/8] rc4030: create custom DMA address space
Date: Wed, 25 Mar 2015 20:10:53 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.4.0

Le 25/03/2015 15:45, Paolo Bonzini a écrit :

On 05/03/2015 23:13, Hervé Poussineau wrote:
Add a new memory region in system address space where DMA address space
definition (the 'translation table') belongs, so we can update on the fly
the DMA address space.

Signed-off-by: Hervé Poussineau <address@hidden>

Would it make sense to just use an IOMMU region for the DMA address space?

I don't really know. Currently, the first user is the dp8393x network card (a 
sysbus device), which is connected through the DMA address space.
It means that *every* read or write access needs to be translated, even those 
accessing 1 or 2 bytes. dp8393x has no direct connection to the system memory.
On some other machines, like the m68k Quadra 800, the dp8393x is only connected 
to the system memory.

A second user is the ESP SCSI card in DMA mode, using the DMA address space 
with the help of the DMA controller.

As DMA address space mapping doesn't change much (except initialization phases), and that it is used for small (1 or 2 bytes) and big transfers (network packets and disk accesses), I thought that an address space was better.


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