dmaengine: rcar-dmac: Add device tree bindings documentation

* Renesas R-Car DMA Controller Device Tree bindings

Renesas R-Car Generation 2 SoCs have have multiple multi-channel DMA

controller instances named DMAC capable of serving multiple clients. Channels

can be dedicated to specific clients or shared between a large number of

clients.

DMA clients are connected to the DMAC ports referenced by an 8-bit identifier

called MID/RID.

Each DMA client is connected to one dedicated port of the DMAC, identified by

an 8-bit port number called the MID/RID. A DMA controller can thus serve up to

256 clients in total. When the number of hardware channels is lower than the

number of clients to be served, channels must be shared between multiple DMA

clients. The association of DMA clients to DMAC channels is fully dynamic and

not described in these device tree bindings.

Required Properties:

- compatible: must contain "renesas,rcar-dmac"

- reg: base address and length of the registers block for the DMAC

- interrupts: interrupt specifiers for the DMAC, one for each entry in

  interrupt-names.

- interrupt-names: one entry per channel, named "ch%u", where %u is the

  channel number ranging from zero to the number of channels minus one.

- clock-names: "fck" for the functional clock

- clocks: a list of phandle + clock-specifier pairs, one for each entry

  in clock-names.

- clock-names: must contain "fck" for the functional clock.

- #dma-cells: must be <1>, the cell specifies the MID/RID of the DMAC port

  connected to the DMA client

- dma-channels: number of DMA channels

Example: R8A7790 (R-Car H2) SYS-DMACs

	dmac0: dma-controller@e6700000 {

		compatible = "renesas,rcar-dmac";

		reg = <0 0xe6700000 0 0x20000>;

		interrupts = <0 197 IRQ_TYPE_LEVEL_HIGH

			      0 200 IRQ_TYPE_LEVEL_HIGH

			      0 201 IRQ_TYPE_LEVEL_HIGH

			      0 202 IRQ_TYPE_LEVEL_HIGH

			      0 203 IRQ_TYPE_LEVEL_HIGH

			      0 204 IRQ_TYPE_LEVEL_HIGH

			      0 205 IRQ_TYPE_LEVEL_HIGH

			      0 206 IRQ_TYPE_LEVEL_HIGH

			      0 207 IRQ_TYPE_LEVEL_HIGH

			      0 208 IRQ_TYPE_LEVEL_HIGH

			      0 209 IRQ_TYPE_LEVEL_HIGH

			      0 210 IRQ_TYPE_LEVEL_HIGH

			      0 211 IRQ_TYPE_LEVEL_HIGH

			      0 212 IRQ_TYPE_LEVEL_HIGH

			      0 213 IRQ_TYPE_LEVEL_HIGH

			      0 214 IRQ_TYPE_LEVEL_HIGH>;

		interrupt-names = "error",

				"ch0", "ch1", "ch2", "ch3",

				"ch4", "ch5", "ch6", "ch7",

				"ch8", "ch9", "ch10", "ch11",

				"ch12", "ch13", "ch14";

		clocks = <&mstp2_clks R8A7790_CLK_SYS_DMAC0>;

		clock-names = "fck";

		#dma-cells = <1>;

		dma-channels = <15>;

	};

	dmac1: dma-controller@e6720000 {

		compatible = "renesas,rcar-dmac";

		reg = <0 0xe6720000 0 0x20000>;

		interrupts = <0 220 IRQ_TYPE_LEVEL_HIGH

			      0 216 IRQ_TYPE_LEVEL_HIGH

			      0 217 IRQ_TYPE_LEVEL_HIGH

			      0 218 IRQ_TYPE_LEVEL_HIGH

			      0 219 IRQ_TYPE_LEVEL_HIGH

			      0 308 IRQ_TYPE_LEVEL_HIGH

			      0 309 IRQ_TYPE_LEVEL_HIGH

			      0 310 IRQ_TYPE_LEVEL_HIGH

			      0 311 IRQ_TYPE_LEVEL_HIGH

			      0 312 IRQ_TYPE_LEVEL_HIGH

			      0 313 IRQ_TYPE_LEVEL_HIGH

			      0 314 IRQ_TYPE_LEVEL_HIGH

			      0 315 IRQ_TYPE_LEVEL_HIGH

			      0 316 IRQ_TYPE_LEVEL_HIGH

			      0 317 IRQ_TYPE_LEVEL_HIGH

			      0 318 IRQ_TYPE_LEVEL_HIGH>;

		interrupt-names = "error",

				"ch0", "ch1", "ch2", "ch3",

				"ch4", "ch5", "ch6", "ch7",

				"ch8", "ch9", "ch10", "ch11",

				"ch12", "ch13", "ch14";

		clocks = <&mstp2_clks R8A7790_CLK_SYS_DMAC1>;

		clock-names = "fck";

		#dma-cells = <1>;

		dma-channels = <15>;

	};