+- #mbox-cells: Must be 2.
+ <&phandle type channel>
+ phandle : Label name of controller
+ type : Channel type
+ channel : Channel number
+
+ This MU support 4 type of unidirectional channels, each type
+ has 4 channels. A total of 16 channels. Following types are
+ supported:
+ 0 - TX channel with 32bit transmit register and IRQ transmit
+ acknowledgment support.
+ 1 - RX channel with 32bit receive register and IRQ support
+ 2 - TX doorbell channel. Without own register and no ACK support.
+ 3 - RX doorbell channel.
+
+Optional properties:
+-------------------
+- clocks : phandle to the input clock.
+- fsl,mu-side-b : Should be set for side B MU.