"Devices" don't call functions. Drivers do, or in this case, it looksDevices under kernel drivers control must call iommu_device_use_dma_api()
before driver probes. The driver binding process must be aborted if it
returns failure.
like the bus DMA code (platform, amba, fsl, pci, etc).
These functions are EXPORT_SYMBOL_GPL(), but it looks like all the
callers are built-in, so maybe the export is unnecessary?
You use "iommu"/"IOMMU" and "dma"/"DMA" interchangeably above. Would
be easier to read if you picked one.