Hello xen-devel, 
I'm reading the code of xen arm smmu in drivers/passthrough/arm, and I have some questions that confused me.
I think if the board use SMMU, xen will take charge of it before dom0 boot, and will not pass the node of SMMU to dom0 in device tree,
so my question is how dom0 use SMMU? or can dom0 use SMMU? What dom0 use if it wants to use IOMMU?
What about domU? The SMMU could be passed to domU?
Thank you!