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

From: Anthony Liguori
Subject: Re: [kvm-devel] [Qemu-devel] [PATCH 2/6] PCI DMA API
Date: Sun, 30 Mar 2008 09:56:04 -0500
User-agent: Thunderbird (X11/20080227)

Avi Kivity wrote:
Anthony Liguori wrote:
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.

State for the dma controller.

I think Blue is calling for chaining of dma mappings, no? Something similar is being proposed for the Linux dma api.

The way I envision chaining is:

virtio-blk calls pci_device_dma_map with a PhysIOVector A
pci_device_dma_map calls into PCI IOMMU (if necessary) to translate PhysIOVector A to PhysIOVector B pci_device_dma_map then calls into platform DMA engine to translate PhysIOVector B to PhysIOVector C
pci_device_dma_map frees PhysIOVector B and returns PhysIOVector C


Anthony Liguori

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