Standard properties of devicetrees.

The #address-cells and #size-cells properties are not inherited from ancestors in the devicetree. They shall be explicitly defined.

A DTSpec-compliant boot program shall supply #address-cells and #size-cells on all nodes that have children.

If missing, a client program should assume a default value of 2 for #address-cells, and a value of 1 for #size-cells.

The reg property describes the address of the device’s resources within the address space defined by its parent bus. Most commonly this means the offsets and lengths of memory-mapped IO register blocks, but may have a different meaning on some bus types. Addresses in the address space defined by the root node are CPU real addresses.

The value is a <prop-encoded-array>, composed of an arbitrary number of pairs of address and length, <address length>. The number of <u32> cells required to specify the address and length are bus-specific and are specified by the #address-cells and #size-cells properties in the parent of the device node. If the parent node specifies a value of 0 for #size-cells, the length field in the value of reg shall be omitted.

Seems to be PowerPC only.

The format of the value of the ranges property is an arbitrary number of triplets of (child-bus-address, parent-bus-address, length)

• The child-bus-address is a physical address within the child bus’ address space. The number of cells to represent the address is bus dependent and can be determined from the #address-cells of this node (the node in which the ranges property appears).
• The parent-bus-address is a physical address within the parent bus’ address space. The number of cells to represent the parent address is bus dependent and can be determined from the #address-cells property of the node that defines the parent’s address space.
• The length specifies the size of the range in the child’s address space. The number of cells to represent the size can be determined from the #size-cells of this node (the node in which the ranges property appears).

If the property is defined with an <empty> value, it specifies that the parent and child address space is identical, and no address translation is required.

If the property is not present in a bus node, it is assumed that no mapping exists between children of the node and the parent address space.