dt-bindings: Add DT bindings info for FlexRM ring manager

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 3nd 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 atleast 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>;

};