ARM: add alphascale,acc.txt bindings documentation

ACC is for AlphaScale Clock Controller.
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Olof Johansson <olof@lixom.net>

Documentation/devicetree/bindings/clock/alphascale,acc.txt

+Alphascale Clock Controller
+
+The ACC (Alphascale Clock Controller) is responsible of choising proper
+clock source, setting deviders and clock gates.
+
+Required properties for the ACC node:
+ - compatible: must be "alphascale,asm9260-clock-controller"
+ - reg: must contain the ACC register base and size
+ - #clock-cells : shall be set to 1.
+
+Simple one-cell clock specifier format is used, where the only cell is used
+as an index of the clock inside the provider.
+It is encouraged to use dt-binding for clock index definitions. SoC specific
+dt-binding should be included to the device tree descriptor. For example
+Alphascale ASM9260:
+#include <dt-bindings/clock/alphascale,asm9260.h>
+
+This binding contains two types of clock providers:
+ _AHB_ - AHB gate;
+ _SYS_ - adjustable clock source. Not all peripheral have _SYS_ clock provider.
+All clock specific details can be found in the SoC documentation.
+CLKID_AHB_ROM		0
+CLKID_AHB_RAM		1
+CLKID_AHB_GPIO		2
+CLKID_AHB_MAC		3
+CLKID_AHB_EMI		4
+CLKID_AHB_USB0		5
+CLKID_AHB_USB1		6
+CLKID_AHB_DMA0		7
+CLKID_AHB_DMA1		8
+CLKID_AHB_UART0		9
+CLKID_AHB_UART1		10
+CLKID_AHB_UART2		11
+CLKID_AHB_UART3		12
+CLKID_AHB_UART4		13
+CLKID_AHB_UART5		14
+CLKID_AHB_UART6		15
+CLKID_AHB_UART7		16
+CLKID_AHB_UART8		17
+CLKID_AHB_UART9		18
+CLKID_AHB_I2S0		19
+CLKID_AHB_I2C0		20
+CLKID_AHB_I2C1		21
+CLKID_AHB_SSP0		22
+CLKID_AHB_IOCONFIG	23
+CLKID_AHB_WDT		24
+CLKID_AHB_CAN0		25
+CLKID_AHB_CAN1		26
+CLKID_AHB_MPWM		27
+CLKID_AHB_SPI0		28
+CLKID_AHB_SPI1		29
+CLKID_AHB_QEI		30
+CLKID_AHB_QUADSPI0	31
+CLKID_AHB_CAMIF		32
+CLKID_AHB_LCDIF		33
+CLKID_AHB_TIMER0	34
+CLKID_AHB_TIMER1	35
+CLKID_AHB_TIMER2	36
+CLKID_AHB_TIMER3	37
+CLKID_AHB_IRQ		38
+CLKID_AHB_RTC		39
+CLKID_AHB_NAND		40
+CLKID_AHB_ADC0		41
+CLKID_AHB_LED		42
+CLKID_AHB_DAC0		43
+CLKID_AHB_LCD		44
+CLKID_AHB_I2S1		45
+CLKID_AHB_MAC1		46
+
+CLKID_SYS_CPU		47
+CLKID_SYS_AHB		48
+CLKID_SYS_I2S0M		49
+CLKID_SYS_I2S0S		50
+CLKID_SYS_I2S1M		51
+CLKID_SYS_I2S1S		52
+CLKID_SYS_UART0		53
+CLKID_SYS_UART1		54
+CLKID_SYS_UART2		55
+CLKID_SYS_UART3		56
+CLKID_SYS_UART4		56
+CLKID_SYS_UART5		57
+CLKID_SYS_UART6		58
+CLKID_SYS_UART7		59
+CLKID_SYS_UART8		60
+CLKID_SYS_UART9		61
+CLKID_SYS_SPI0		62
+CLKID_SYS_SPI1		63
+CLKID_SYS_QUADSPI	64
+CLKID_SYS_SSP0		65
+CLKID_SYS_NAND		66
+CLKID_SYS_TRACE		67
+CLKID_SYS_CAMM		68
+CLKID_SYS_WDT		69
+CLKID_SYS_CLKOUT	70
+CLKID_SYS_MAC		71
+CLKID_SYS_LCD		72
+CLKID_SYS_ADCANA	73
+
+Example of clock consumer with _SYS_ and _AHB_ sinks.
+uart4: serial@80010000 {
+	compatible = "alphascale,asm9260-uart";
+	reg = <0x80010000 0x4000>;
+	clocks = <&acc CLKID_SYS_UART4>, <&acc CLKID_AHB_UART4>;
+	interrupts = <19>;
+	status = "disabled";
+};
+
+Clock consumer with only one, _AHB_ sink.
+timer0: timer@80088000 {
+	compatible = "alphascale,asm9260-timer";
+	reg = <0x80088000 0x4000>;
+	clocks = <&acc CLKID_AHB_TIMER0>;
+	interrupts = <29>;
+};
+