u-boot/doc/device-tree-bindings/memory/memory.txt

* Memory binding

The memory binding for U-Boot is as in the ePAPR with the following additions:

Optional subnodes can be used defining the memory layout for different board
ID masks. To match a set of board ids, a board-id node may define match-mask
and match-value ints to define a mask to apply to the board id, and the value
that the result should have for the match to be considered valid. The mask
defaults to -1, meaning that the value must fully match the board id.

If subnodes are present, then the /memory node must define these properties:

- #address-cells: should be 1.
- #size-cells: should be 0.

Each subnode must define

 reg - board ID or mask for this subnode
 memory-banks - list of memory banks in the same format as normal

Each subnode may optionally define:

 match-mask - A mask to apply to the board id.  This must be accompanied by
              match-value.
 match-value - The required resulting value of the board id mask for the given
	       node to be considered a match.
 auto-size - Indicates that the value given for a bank is the maximum size,
	     each bank is probed to determine its actual size, which may be
	     smaller


The board id determination is up to the vendor and is not defined by this
binding.

Example:

memory {
	#address-cells = <1>;
	#size-cells = <1>;
	reg = <0x20000000 0x20000000
		0x40000000 0x20000000
		0x60000000 0x20000000
		0x80000000 0x20000000>;
	auto-size;
	board-id@0 {
		match-value = <17>;
		reg = <0x20000000 0x20000000
			0x40000000 0x20000000>;
	};
	board-id@1 {
		match-mask = <2>;
		match-value = <2>;
		reg = <0x20000000 0x20000000
			0x40000000 0x20000000
			0x60000000 0x20000000
			0x80000000 0x20000000
			0xa0000000 0x20000000
			0xc0000000 0x20000000
			0xe0000000 0x20000000>;
	};
};


This shows a system with the following properties:
* Default of 2GB of memory, auto-sized, so could be smaller
* 3.5GB of memory (with no auto-size) if (board id & 2) is 2
* 1GB of memory (with no auto-size) if board id is 17.