dt-bindings: mailbox: Document Hi6220 mailbox driver

Document DT binding for Hisilicon Hi6220 mailbox driver.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

diff --git a/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt b/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt
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+Hisilicon Hi6220 Mailbox Driver
+===============================
+
+Hisilicon Hi6220 mailbox supports up to 32 channels. Each channel
+is unidirectional with a maximum message size of 8 words. I/O is
+performed using register access (there is no DMA) and the cell
+raises an interrupt when messages are received.
+
+Mailbox Device Node:
+====================
+
+Required properties:
+--------------------
+- compatible:          Shall be "hisilicon,hi6220-mbox"
+- reg:                 Contains the mailbox register address range (base
+                       address and length); the first item is for IPC
+                       registers, the second item is shared buffer for
+                       slots.
+- #mbox-cells:         Common mailbox binding property to identify the number
+                       of cells required for the mailbox specifier. Must be 3.
+                       <&phandle slot_id dst_irq ack_irq>
+                         phandle: Label name of mailbox controller
+                         slot_id: Slot id used either for TX or RX
+                         dst_irq: IRQ identifier index number which used by MCU
+                         ack_irq: IRQ identifier index number with generating a
+                                  TX/RX interrupt to application processor,
+                                  mailbox driver uses it to acknowledge interrupt
+- interrupts:          Contains the interrupt information for the mailbox
+                       device. The format is dependent on which interrupt
+                       controller the SoCs use.
+
+Optional Properties:
+--------------------
+- hi6220,mbox-tx-noirq: Property of MCU firmware's feature, so mailbox driver
+                       use this flag to ask MCU to enable "automatic idle
+                       flag" mode or IRQ generated mode to acknowledge a TX
+                       completion.
+
+Example:
+--------
+
+       mailbox: mailbox@f7510000 {
+               compatible = "hisilicon,hi6220-mbox";
+               reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */
+                     <0x0 0x06dff800 0x0 0x0800>; /* Mailbox */
+               interrupt-parent = <&gic>;
+               interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
+               #mbox-cells = <3>;
+       };
+
+
+Mailbox client
+===============
+
+Required properties:
+--------------------
+- compatible:          Many (See the client docs).
+- mboxes:              Standard property to specify a Mailbox (See ./mailbox.txt)
+                       Cells must match 'mbox-cells' (See Mailbox Device Node above).
+
+Optional Properties:
+--------------------
+- mbox-names:          Name given to channels seen in the 'mboxes' property.
+
+Example:
+--------
+
+       stub_clock: stub_clock {
+               compatible = "hisilicon,hi6220-stub-clk";
+               hisilicon,hi6220-clk-sram = <&sram>;
+               #clock-cells = <1>;
+               mbox-names = "mbox-tx", "mbox-rx";
+               mboxes = <&mailbox 1 0 11>, <&mailbox 0 1 10>;
+       };