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Re: [Qemu-devel] [PATCH 2/6] PCI DMA API

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 2/6] PCI DMA API
Date: Sun, 30 Mar 2008 10:11:39 -0500
User-agent: Thunderbird (X11/20080227)

Blue Swirl wrote:
On 3/30/08, Anthony Liguori <address@hidden> wrote:
Blue Swirl wrote:
 > On 3/30/08, Anthony Liguori <address@hidden> wrote:
 >> This patch introduces a PCI DMA API and some generic code to support other 
 >>  APIs.  Two types are introduced: PhysIOVector and IOVector.  A DMA API
 >>  maps a PhysIOVector, which is composed of target_phys_addr_t, into an 
 >>  which is composed of void *.
 > This looks like it wouldn't scale to handle the Sparc systems. There
 > we want to make more translation steps from DVMA addresses to physical
 > in DMA controller and IOMMU and only in the final stage to void *. To
 > handle this, probably there should be an opaque parameter and some way
 > to register the translation function. Otherwise the API looks OK.

I think having the PCI DMA API translate PhysIOVector => PhysIOVector
 would help.  Then it becomes pretty easy to just call the DMA controller
 for additional translation from the IOMMU.

 Does that sound right?  I don't quite understand what role the opaque
 parameter would serve.

Devices should not need to know about the underlying buses, so they
can be used in different systems.

I don't think it will be too hard for a device to support multiple buses if we have the DMA API at the bus level. In the future, the per-bus DMA API may have slight, but important differences. For instance, at some point, PCI devices will be capable of recovering from an IO fault and you'd eventually want the DMA API to reflect this for PCI.


Anthony LIguori

 So the translators just call
recursively next ones until we get physical memory. I would use the
opaque parameter as a pointer to each translator's own state
structures. But if you can implement this without the parameter,

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