doc: dt: add documentation for lpc1850-cgu clk driver

Add DT binding documentation for lpc1850-cgu driver.

Signed-off-by: Joachim Eastwood <[e-mail]>
Signed-off-by: Michael Turquette <[e-mail]>

Documentation/devicetree/bindings/clock/lpc1850-cgu.txt

···
+* NXP LPC1850 Clock Generation Unit (CGU)
+
+The CGU generates multiple independent clocks for the core and the
+peripheral blocks of the LPC18xx. Each independent clock is called
+a base clock and itself is one of the inputs to the two Clock
+Control Units (CCUs) which control the branch clocks to the
+individual peripherals.
+
+The CGU selects the inputs to the clock generators from multiple
+clock sources, controls the clock generation, and routes the outputs
+of the clock generators through the clock source bus to the output
+stages. Each output stage provides an independent clock source and
+corresponds to one of the base clocks for the LPC18xx.
+
+ - Above text taken from NXP LPC1850 User Manual.
+
+
+This binding uses the common clock binding:
+    Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+Required properties:
+- compatible:
+	Should be "nxp,lpc1850-cgu"
+- reg:
+	Shall define the base and range of the address space
+	containing clock control registers
+- #clock-cells:
+	Shall have value <1>.  The permitted clock-specifier values
+	are the base clock numbers defined below.
+- clocks:
+	Shall contain a list of phandles for the external input
+	sources to the CGU. The list shall be in the following
+	order: xtal, 32khz, enet_rx_clk, enet_tx_clk, gp_clkin.
+- clock-indices:
+	Shall be an ordered list of numbers defining the base clock
+	number provided by the CGU.
+- clock-output-names:
+	Shall be an ordered list of strings defining the names of
+	the clocks provided by the CGU.
+
+Which base clocks that are available on the CGU depends on the
+specific LPC part. Base clocks are numbered from 0 to 27.
+
+Number:		Name:			Description:
+ 0		BASE_SAFE_CLK		Base safe clock (always on) for WWDT
+ 1		BASE_USB0_CLK		Base clock for USB0
+ 2		BASE_PERIPH_CLK		Base clock for Cortex-M0SUB subsystem,
+					SPI, and SGPIO
+ 3		BASE_USB1_CLK		Base clock for USB1
+ 4		BASE_CPU_CLK		System base clock for ARM Cortex-M core
+					and APB peripheral blocks #0 and #2
+ 5		BASE_SPIFI_CLK		Base clock for SPIFI
+ 6		BASE_SPI_CLK		Base clock for SPI
+ 7		BASE_PHY_RX_CLK		Base clock for Ethernet PHY Receive clock
+ 8		BASE_PHY_TX_CLK		Base clock for Ethernet PHY Transmit clock
+ 9		BASE_APB1_CLK		Base clock for APB peripheral block # 1
+10		BASE_APB3_CLK		Base clock for APB peripheral block # 3
+11		BASE_LCD_CLK		Base clock for LCD
+12		BASE_ADCHS_CLK		Base clock for ADCHS
+13		BASE_SDIO_CLK		Base clock for SD/MMC
+14		BASE_SSP0_CLK		Base clock for SSP0
+15		BASE_SSP1_CLK		Base clock for SSP1
+16		BASE_UART0_CLK		Base clock for UART0
+17		BASE_UART1_CLK		Base clock for UART1
+18		BASE_UART2_CLK		Base clock for UART2
+19		BASE_UART3_CLK		Base clock for UART3
+20		BASE_OUT_CLK		Base clock for CLKOUT pin
+24-21		-			Reserved
+25		BASE_AUDIO_CLK		Base clock for audio system (I2S)
+26 		BASE_CGU_OUT0_CLK	Base clock for CGU_OUT0 clock output
+27 		BASE_CGU_OUT1_CLK	Base clock for CGU_OUT1 clock output
+
+BASE_PERIPH_CLK and BASE_SPI_CLK is only available on LPC43xx.
+BASE_ADCHS_CLK is only available on LPC4370.
+
+
+Example board file:
+
+/ {
+	clocks {
+		xtal: xtal {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <12000000>;
+		};
+
+		xtal32: xtal32 {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <32768>;
+		};
+
+		enet_rx_clk: enet_rx_clk {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+			clock-output-names = "enet_rx_clk";
+		};
+
+		enet_tx_clk: enet_tx_clk {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+			clock-output-names = "enet_tx_clk";
+		};
+
+		gp_clkin: gp_clkin {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+			clock-output-names = "gp_clkin";
+		};
+	};
+
+	soc {
+		cgu: clock-controller@40050000 {
+			compatible = "nxp,lpc1850-cgu";
+			reg = <0x40050000 0x1000>;
+			#clock-cells = <1>;
+			clocks = <&xtal>, <&creg_clk 1>, <&enet_rx_clk>, <&enet_tx_clk>, <&gp_clkin>;
+		};
+
+		/* A CGU and CCU clock consumer */
+		lcdc: lcdc@40008000 {
+			...
+			clocks = <&cgu BASE_LCD_CLK>, <&ccu1 CLK_CPU_LCD>;
+			clock-names = "clcdclk", "apb_pclk";
+			...
+		};
+	};
+};