OMAP2+ Mailbox Driver
=====================

The OMAP mailbox hardware facilitates communication between different processors
using a queued mailbox interrupt mechanism. The IP block is external to the
various processor subsystems and is connected on an interconnect bus. The
communication is achieved through a set of registers for message storage and
interrupt configuration registers.

Each mailbox IP block has a certain number of h/w fifo queues and output
interrupt lines. An output interrupt line is routed to an interrupt controller
within a processor subsystem, and there can be more than one line going to a
specific processor's interrupt controller. The interrupt line connections are
fixed for an instance and are dictated by the IP integration into the SoC
(excluding the SoCs that have a Interrupt Crossbar IP). Each interrupt line is
programmable through a set of interrupt configuration registers, and have a rx
and tx interrupt source per h/w fifo. Communication between different processors
is achieved through the appropriate programming of the rx and tx interrupt
sources on the appropriate interrupt lines.

The number of h/w fifo queues and interrupt lines dictate the usable registers.
All the current OMAP SoCs except for the newest DRA7xx SoC has a single IP
instance. DRA7xx has multiple instances with different number of h/w fifo queues
and interrupt lines between different instances. The interrupt lines can also be
routed to different processor sub-systems on DRA7xx as they are routed through
the Crossbar, a kind of interrupt router/multiplexer.

Mailbox Device Node:
====================
A Mailbox device node is used to represent a Mailbox IP instance within a SoC.
The sub-mailboxes are represented as child nodes of this parent node.

Required properties:
--------------------
- compatible:		Should be one of the following,
			    "ti,omap2-mailbox" for OMAP2420, OMAP2430 SoCs
			    "ti,omap3-mailbox" for OMAP3430, OMAP3630 SoCs
			    "ti,omap4-mailbox" for OMAP44xx, OMAP54xx, AM33xx,
						   AM43xx and DRA7xx SoCs
- reg:			Contains the mailbox register address range (base
			address and length)
- interrupts:		Contains the interrupt information for the mailbox
			device. The format is dependent on which interrupt
			controller the OMAP device uses
- ti,hwmods:		Name of the hwmod associated with the mailbox
- #mbox-cells:		Common mailbox binding property to identify the number
			of cells required for the mailbox specifier. Should be
			1
- ti,mbox-num-users:	Number of targets (processor devices) that the mailbox
			device can interrupt
- ti,mbox-num-fifos:	Number of h/w fifo queues within the mailbox IP block

Child Nodes:
============
A child node is used for representing the actual sub-mailbox device that is
used for the communication between the host processor and a remote processor.
Each child node should have a unique node name across all the different
mailbox device nodes.

Required properties:
--------------------
- ti,mbox-tx:		sub-mailbox descriptor property defining a Tx fifo
- ti,mbox-rx:		sub-mailbox descriptor property defining a Rx fifo

Sub-mailbox Descriptor Data
---------------------------
Each of the above ti,mbox-tx and ti,mbox-rx properties should have 3 cells of
data that represent the following:
    Cell #1 (fifo_id) - mailbox fifo id used either for transmitting
                        (ti,mbox-tx) or for receiving (ti,mbox-rx)
    Cell #2 (irq_id)  - irq identifier index number to use from the parent's
                        interrupts data. Should be 0 for most of the cases, a
                        positive index value is seen only on mailboxes that have
                        multiple interrupt lines connected to the MPU processor.
    Cell #3 (usr_id)  - mailbox user id for identifying the interrupt line
                        associated with generating a tx/rx fifo interrupt.

Mailbox Users:
==============
A device needing to communicate with a target processor device should specify
them using the common mailbox binding properties, "mboxes" and the optional
"mbox-names" (please see Documentation/devicetree/bindings/mailbox/mailbox.txt
for details). Each value of the mboxes property should contain a phandle to the
mailbox controller device node and an args specifier that will be the phandle to
the intended sub-mailbox child node to be used for communication. The equivalent
"mbox-names" property value can be used to give a name to the communication channel
to be used by the client user.


Example:
--------

/* OMAP4 */
mailbox: mailbox@4a0f4000 {
	compatible = "ti,omap4-mailbox";
	reg = <0x4a0f4000 0x200>;
	interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
	ti,hwmods = "mailbox";
	#mbox-cells = <1>;
	ti,mbox-num-users = <3>;
	ti,mbox-num-fifos = <8>;
	mbox_ipu: mbox_ipu {
		ti,mbox-tx = <0 0 0>;
		ti,mbox-rx = <1 0 0>;
	};
	mbox_dsp: mbox_dsp {
		ti,mbox-tx = <3 0 0>;
		ti,mbox-rx = <2 0 0>;
	};
};

dsp {
	...
	mboxes = <&mailbox &mbox_dsp>;
	...
};

/* AM33xx */
mailbox: mailbox@480C8000 {
	compatible = "ti,omap4-mailbox";
	reg = <0x480C8000 0x200>;
	interrupts = <77>;
	ti,hwmods = "mailbox";
	#mbox-cells = <1>;
	ti,mbox-num-users = <4>;
	ti,mbox-num-fifos = <8>;
	mbox_wkupm3: wkup_m3 {
		ti,mbox-tx = <0 0 0>;
		ti,mbox-rx = <0 0 3>;
	};
};