Re: [Xen-devel] Driver domain on ARM questions

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 15 Oct 2014, Andrii Tseglytskyi wrote:
> Hi,
> 
> Can someone clarify the following questions:
> 
> - is any special support required in Xen code to implement driver
> domain on ARM ?

Not particularly, but you need to be able to assign the device to the
driver domain so the device needs to be behind an SMMU.


> - is it possible to have one to one memory mapping in dom0 and driver
> domain simultaneously ?

We would want to avoid the 1:1 mapping in driver domains, so this is why
we need the device to be behind an SMMU.


> - if answer to previous one is NO, how can I make DMA working in driver 
> domain ?

The best and more performant option is to use an SMMU.
Otherwise you can:

- use XENMEM_exchange to make a guest buffer contiguous in machine
memory space and bounce all the dma requests on the buffer using
swiotlb-xen. It is not going to have great performances but it should
work well.

- use the 1:1 hack in the driver domain


> I found only high level concepts:
> 
> http://events.linuxfoundation.org/sites/events/files/slides/alsf13_stabellini.pdf
> http://pdub.net/proj/usenix08boston/xen_drive/resources/xensummit/slides/14_SangBumSuh.pdf
> 
> Thank you for any info, useful links or so.
> 
> Regards,
> Andrii
> 
> -- 
> 
> Andrii Tseglytskyi | Embedded Dev
> GlobalLogic
> www.globallogic.com
> 

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