dts/bindings/clock/st,stm32-rcc.yaml

# Copyright (c) 2021, Linaro ltd
# SPDX-License-Identifier: Apache-2.0

description: |
  STM32 Reset and Clock controller node.
  This node is in charge of system clock ('SYSCLK') source selection and controlling
  clocks for AHB (Advanced High Performance) and APB (Advanced Peripheral) bus domains.

  Configuring STM32 Reset and Clock controller node:

  System clock source should be selected amongst the clock nodes available in "clocks"
  node (typically 'clk_hse, clk_hsi', 'pll', ...).
  As part of this node configuration, SYSCLK frequency should also be defined, using
  "clock-frequency" property.
  Last, bus clocks (typically HCLK, PCLK1, PCLK2) should be configured using matching
  prescaler properties.
  Here is an example of correctly configured rcc node:
  &rcc {
           clocks = <&pll>;  /* Set pll as SYSCLK source */
           clock-frequency = <DT_FREQ_M(80)>; /* SYSCLK runs at 80MHz */
           ahb-prescaler = <1>;
           apb1-presacler = <1>;
           apb2-presacler = <1>;
  }

  Specifying a gated clock:

  To specify a gated clock, a peripheral should define a "clocks" property encoded
  in the following way:
  ... {
           ...
           clocks = <&rcc STM32_CLOCK_BUS_APB2 0x00000020>;
           ...
  }
  After the phandle referring to rcc node, the first index specifies the registers of
  the bus controlling the peripheral and the second index specifies the bit used to
  control the peripheral clock in that bus register.

compatible: "st,stm32-rcc"

include: [clock-controller.yaml, base.yaml]

properties:
    reg:
      required: true

    "#clock-cells":
      const: 2

    clock-frequency:
      required: true
      type: int
      description: |
        default frequency in Hz for clock output

    ahb-prescaler:
      type: int
      required: true
      enum:
        - 1
        - 2
        - 4
        - 8
        - 16
        - 64
        - 128
        - 256
        - 512
      description: |
          AHB prescaler. Sets a HCLK frequency (feeding Cortex-M Systick)
          lower than SYSCLK frequency (actual core frequency).
          The HCLK clocks CPU, AHB, memories and DMA.

    apb1-prescaler:
      type: int
      required: true
      enum:
        - 1
        - 2
        - 4
        - 8
        - 16

    apb2-prescaler:
      type: int
      required: true
      enum:
        - 1
        - 2
        - 4
        - 8
        - 16

clock-cells:
  - bus
  - bits