DeviceTree Booting

Device-tree compatible SH bootloaders are expected to provide the physical address of the device tree blob in r4. Since legacy bootloaders did not guarantee any particular initial register state, kernels built to inter-operate with old bootloaders must either use a builtin DTB or select a legacy board option (something other than CONFIG_SH_DEVICE_TREE) that does not use device tree. Support for the latter is being phased out in favor of device tree.