dt-bindings: Document STM32MP1 Reset Clock Controller (RCC) bindings

STMicroelectronics STM32 Peripheral Reset Clock Controller

==========================================================

The RCC IP is both a reset and a clock controller.

RCC makes also power management (resume/supend and wakeup interrupt).

Please also refer to reset.txt for common reset controller binding usage.

Please also refer to clock-bindings.txt for common clock controller

binding usage.

Required properties:

- compatible: "st,stm32mp1-rcc", "syscon"

- reg: should be register base and length as documented in the datasheet

- #clock-cells: 1, device nodes should specify the clock in their

  "clocks" property, containing a phandle to the clock device node,

  an index specifying the clock to use.

- #reset-cells: Shall be 1

- interrupts: Should contain a general interrupt line and a interrupt line

  to the wake-up of processor (CSTOP).

Example:

	rcc: rcc@50000000 {

		compatible = "st,stm32mp1-rcc", "syscon";

		reg = <0x50000000 0x1000>;

		#clock-cells = <1>;

		#reset-cells = <1>;

		interrupts = <GIC_SPI 5 IRQ_TYPE_NONE>,

			     <GIC_SPI 145 IRQ_TYPE_NONE>;

	};

Specifying clocks

=================

All available clocks are defined as preprocessor macros in

dt-bindings/clock/stm32mp1-clks.h header and can be used in device

tree sources.

Specifying softreset control of devices

=======================================

Device nodes should specify the reset channel required in their "resets"

property, containing a phandle to the reset device node and an index specifying

which channel to use.

The index is the bit number within the RCC registers bank, starting from RCC

base address.

It is calculated as: index = register_offset / 4 * 32 + bit_offset.

Where bit_offset is the bit offset within the register.

For example on STM32MP1, for LTDC reset:

 ltdc = APB4_RSTSETR_offset / 4 * 32 + LTDC_bit_offset

      = 0x180 / 4 * 32 + 0 = 3072

The list of valid indices for STM32MP1 is available in:

include/dt-bindings/reset-controller/stm32mp1-resets.h

This file implements defines like:

#define LTDC_R	3072