On Fri, Feb 05, 2021 at 02:26:40PM -0800, Saravana Kannan wrote:

Not all DT bindings are mandatory bindings. Add support for optional DT
bindings and mark iommus, iommu-map, dmas as optional DT bindings.

I don't think we can say these are optional or not. It's got to be a 
driver decision somehow.

For example, if IOMMU is optional, what happens with this sequence:

driver probes without IOMMU
driver calls dma_map_?()
IOMMU driver probes
h/w accesses DMA buffer --> BOOM!