linux-arkmicro/linux/Documentation/devicetree/bindings/clock/st,stm32-rcc.txt

STMicroelectronics STM32 Reset and Clock Controller
===================================================

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

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

Required properties:
- compatible: Should be:
  "st,stm32f42xx-rcc"
  "st,stm32f469-rcc"
  "st,stm32f746-rcc"
- reg: should be register base and length as documented in the
  datasheet
- #reset-cells: 1, see below
- #clock-cells: 2, device nodes should specify the clock in their "clocks"
  property, containing a phandle to the clock device node, an index selecting
  between gated clocks and other clocks and an index specifying the clock to
  use.
- clocks: External oscillator clock phandle
  - high speed external clock signal (HSE)
  - external I2S clock (I2S_CKIN)

Example:

	rcc: rcc@40023800 {
		#reset-cells = <1>;
		#clock-cells = <2>
		compatible = "st,stm32f42xx-rcc", "st,stm32-rcc";
		reg = <0x40023800 0x400>;
		clocks = <&clk_hse>, <&clk_i2s_ckin>;
	};

Specifying gated clocks
=======================

The primary index must be set to 0.

The secondary index is the bit number within the RCC register bank, starting
from the first RCC clock enable register (RCC_AHB1ENR, address offset 0x30).

It is calculated as: index = register_offset / 4 * 32 + bit_offset.
Where bit_offset is the bit offset within the register (LSB is 0, MSB is 31).

To simplify the usage and to share bit definition with the reset and clock
drivers of the RCC IP, macros are available to generate the index in
human-readble format.

For STM32F4 series, the macro are available here:
 - include/dt-bindings/mfd/stm32f4-rcc.h

Example:

	/* Gated clock, AHB1 bit 0 (GPIOA) */
	... {
		clocks = <&rcc 0 STM32F4_AHB1_CLOCK(GPIOA)>
	};

	/* Gated clock, AHB2 bit 4 (CRYP) */
	... {
		clocks = <&rcc 0 STM32F4_AHB2_CLOCK(CRYP)>
	};

Specifying other clocks
=======================

The primary index must be set to 1.

The secondary index is bound with the following magic numbers:

	0	SYSTICK
	1	FCLK
	2	CLK_LSI		(low-power clock source)
	3	CLK_LSE		(generated from a 32.768 kHz low-speed external
				 crystal or ceramic resonator)
	4	CLK_HSE_RTC	(HSE division factor for RTC clock)
	5	CLK_RTC		(real-time clock)
	6	PLL_VCO_I2S	(vco frequency of I2S pll)
	7	PLL_VCO_SAI	(vco frequency of SAI pll)
	8	CLK_LCD		(LCD-TFT)
	9	CLK_I2S		(I2S clocks)
	10	CLK_SAI1	(audio clocks)
	11	CLK_SAI2
	12	CLK_I2SQ_PDIV	(post divisor of pll i2s q divisor)
	13	CLK_SAIQ_PDIV	(post divisor of pll sai q divisor)

	14	CLK_HSI		(Internal ocscillator clock)
	15	CLK_SYSCLK	(System Clock)
	16	CLK_HDMI_CEC	(HDMI-CEC clock)
	17	CLK_SPDIF	(SPDIF-Rx clock)
	18	CLK_USART1	(U(s)arts clocks)
	19	CLK_USART2
	20	CLK_USART3
	21	CLK_UART4
	22	CLK_UART5
	23	CLK_USART6
	24	CLK_UART7
	25	CLK_UART8
	26	CLK_I2C1	(I2S clocks)
	27	CLK_I2C2
	28	CLK_I2C3
	29	CLK_I2C4
	30	CLK_LPTIMER	(LPTimer1 clock)
)

Example:

	/* Misc clock, FCLK */
	... {
		clocks = <&rcc 1 STM32F4_APB1_CLOCK(TIM2)>
	};


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, for CRC reset:
  crc = AHB1RSTR_offset / 4 * 32 + CRCRST_bit_offset = 0x10 / 4 * 32 + 12 = 140

example:

	timer2 {
		resets	= <&rcc STM32F4_APB1_RESET(TIM2)>;
	};