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

[Anthony Liguori <aliguori@us.ibm.com>]

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

Regards,

Anthony Liguori