dma: Add Xilinx AXI DMA DT Binding Documentation

Xilinx AXI DMA engine, it does transfers between memory and AXI4 stream

target devices. It can be configured to have one channel or two channels.

If configured as two channels, one is to transmit to the device and another

is to receive from the device.

Required properties:

- compatible: Should be "xlnx,axi-dma-1.00.a"

- #dma-cells: Should be <1>, see "dmas" property below

- reg: Should contain DMA registers location and length.

- dma-channel child node: Should have atleast one channel and can have upto

	two channels per device. This node specifies the properties of each

	DMA channel (see child node properties below).

Optional properties:

- xlnx,include-sg: Tells whether configured for Scatter-mode in

	the hardware.

Required child node properties:

- compatible: It should be either "xlnx,axi-dma-mm2s-channel" or

	"xlnx,axi-dma-s2mm-channel".

- interrupts: Should contain per channel DMA interrupts.

- xlnx,datawidth: Should contain the stream data width, take values

	{32,64...1024}.

Option child node properties:

- xlnx,include-dre: Tells whether hardware is configured for Data

	Realignment Engine.

Example:

++++++++

axi_dma_0: axidma@40400000 {

	compatible = "xlnx,axi-dma-1.00.a";

	#dma_cells = <1>;

	reg = < 0x40400000 0x10000 >;

	dma-channel@40400000 {

		compatible = "xlnx,axi-dma-mm2s-channel";

		interrupts = < 0 59 4 >;

		xlnx,datawidth = <0x40>;

	} ;

	dma-channel@40400030 {

		compatible = "xlnx,axi-dma-s2mm-channel";

		interrupts = < 0 58 4 >;

		xlnx,datawidth = <0x40>;

	} ;

} ;

* DMA client

Required properties:

- dmas: a list of <[DMA device phandle] [Channel ID]> pairs,

	where Channel ID is '0' for write/tx and '1' for read/rx

	channel.

- dma-names: a list of DMA channel names, one per "dmas" entry

Example:

++++++++

dmatest_0: dmatest@0 {

	compatible ="xlnx,axi-dma-test-1.00.a";

	dmas = <&axi_dma_0 0

		&axi_dma_0 1>;

	dma-names = "dma0", "dma1";

} ;