of_dma_get_max_cpu_address
dt_zone_dma_limit = of_dma_get_max_cpu_address(NULL);
subtree_max_addr = of_dma_get_max_cpu_address(child);
cpu_addr = of_dma_get_max_cpu_address(np);
phys_addr_t of_dma_get_max_cpu_address(struct device_node *np);