Broadcom FlexRM Ring Manager
============================
The Broadcom FlexRM ring manager provides a set of rings which can be
used to submit work to offload engines. An SoC may have multiple FlexRM
hardware blocks. There is one device tree entry per FlexRM block. The
FlexRM driver will create a mailbox-controller instance for given FlexRM
hardware block where each mailbox channel is a separate FlexRM ring.

Required properties:
--------------------
- compatible:	Should be "brcm,iproc-flexrm-mbox"
- reg:		Specifies base physical address and size of the FlexRM
		ring registers
- msi-parent:	Phandles (and potential Device IDs) to MSI controllers
		The FlexRM engine will send MSIs (instead of wired
		interrupts) to CPU. There is one MSI for each FlexRM ring.
		Refer devicetree/bindings/interrupt-controller/msi.txt
- #mbox-cells:	Specifies the number of cells needed to encode a mailbox
		channel. This should be 3.

		The 1st cell is the mailbox channel number.

		The 2nd cell contains MSI completion threshold. This is the
		number of completion messages for which FlexRM will inject
		one MSI interrupt to CPU.

		The 3rd cell contains MSI timer value representing time for
		which FlexRM will wait to accumulate N completion messages
		where N is the value specified by 2nd cell above. If FlexRM
		does not get required number of completion messages in time
		specified by this cell then it will inject one MSI interrupt
		to CPU provided at least one completion message is available.

Optional properties:
--------------------
- dma-coherent:	Present if DMA operations made by the FlexRM engine (such
		as DMA descriptor access, access to buffers pointed by DMA
		descriptors and read/write pointer updates to DDR) are
		cache coherent with the CPU.

Example:
--------
crypto_mbox: mbox@67000000 {
	compatible = "brcm,iproc-flexrm-mbox";
	reg = <0x67000000 0x200000>;
	msi-parent = <&gic_its 0x7f00>;
	#mbox-cells = <3>;
};

crypto@672c0000 {
	compatible = "brcm,spu2-v2-crypto";
	reg = <0x672c0000 0x1000>;
	mboxes = <&crypto_mbox 0 0x1 0xffff>,
		 <&crypto_mbox 1 0x1 0xffff>,
		 <&crypto_mbox 16 0x1 0xffff>,
		 <&crypto_mbox 17 0x1 0xffff>,
		 <&crypto_mbox 30 0x1 0xffff>,
		 <&crypto_mbox 31 0x1 0xffff>;
};