PMIC hardware components

1 Article purpose[edit]

The purpose of this article is to:

  • list the PMIC hardware components that might be integrated in the different boards
  • link these components to the corresponding software framework(s)
  • point to the datasheet(s) of these components
  • explain, when necessary, how to configure these components.

2 Software frameworks[edit]

Domain Peripheral Software components Comment
OP-TEE Linux STM32Cube
PMIC STPMIC1 OP-TEE overview Regulator overview Watchdog overview U-Boot

3 STPMIC1[edit]

3.1 Description[edit]

The STPMIC1 is a device that handles the power supplies for some STM32MP boards. The STPMIC1 main features are:

  • configuration via I²C bus,
  • 10 regulators of different kinds with over-current protection,
  • 3 power switches for USB supplies,
  • a power-on key input,
  • a watchdog,
  • a thermal protection,
  • a NORMAL mode and an ALTERNATE mode that is used for system suspend.

The user manual is available here: NOT YET AVAILABLE

3.2 Support in Linux Kernel[edit]

The STPMIC1 driver is used to handle STPMIC1 Power Management Integrated Circuit (PMIC). The driver is composed of several parts:

  • The core driver
  • The regulator driver
  • The watchdog driver
  • The input driver

The thermal feature is not supported.

3.2.1 Core driver[edit]

The core implements the Multi-Function Devices Framework API.

  • It is probed by the I²C framework.
  • It handles communication with the PMIC via I²C.
  • It probes the others STPMIC1 drivers (input, watchdog....).
  • It acts as an interrupt controller for the other drivers.

Source code:

 include/linux/mfd/stpmic1.h  
 drivers/mfd/stpmic1.c  


Bindings are described in:

 Documentation/devicetree/bindings/mfd/st,stpmic1.txt 

3.2.2 Regulator driver[edit]

The driver implements the Regulator framework API

  • Each BUCK, LDO or POWER SWITCH inside the STPMIC1 device is presented as a voltage regulator.
  • Power switches are presented as fixed voltage sources. Voltage can not be set.
  • The driver does not handle the suspend configuration. This is done by the Secure Monitor.

Source code:

 drivers/regulator/stpmic1_regulator.c  

Bindings are described in:

 Documentation/devicetree/bindings/regulator/st,stpmic1-regulator.txt 

3.2.3 Watchdog driver[edit]

The driver implements the Watchdog framework API

When enabled, a watchdog device is available for the user-land. As soon as a user has started to write in the watchdog it is armed in the PMIC. When the watchdog timer expires, the PMIC shuts down.

Source code:

 drivers/watchdog/stpmic1_wdt.c  

Bindings are described in:

 Documentation/devicetree/bindings/watchdog/st,stpmic1-wdt.txt 

3.2.4 Input driver[edit]

The driver implements the Input framework API.

The driver exposes a single key (KEY_POWER) that can be used as any standard input device in /dev/input/eventX

Source code:

 drivers/input/misc/stpmic1_onkey.c 

Bindings are described in:

 Documentation/devicetree/bindings/input/st,stpmic1-onkey.txt 

3.2.5 Kernel Configuration[edit]

With kernel menuconfig, enable following configurations:

  • core part: MFD_STPMIC1
  • regulator: REGULATOR_STPMIC1
  • watchdog: STPMIC1_WATCHDOG
  • input: INPUT_STPMIC1_ONKEY

3.2.6 SCMI version[edit]

The PMIC can also be accessed via SCMI protocol. If this option is chosen, the kernel does not instantiate any linux STPMIC1 driver but instead it uses SCMI regulators to control power supplies. As the PMIC driver is fully handled in OP-TEE the I2C bus can be secured.

3.3 Support in U-BOOT[edit]

3.3.1 Non Secure version[edit]

STPMIC1 is used by U-Boot to:

  • Control regulators used by other drivers (mmc-supply for SDCard for example, usb vbus)
  • Trace pmic startup reason

STMPIC is supported with existing uclass of the 'Driver Model' described in doc/driver-model/pmic-framework.rst .

The STPMIC1 is available with the existing commands:

  • pmic (CONFIG_CMD_PMIC)
  • regulator (CONFIG_CMD_REGULATOR)
  • poweroff (CONFIG_CMD_POWEROFF)

SPTMIC1 driver supports configuration via device-tree; the bindings, same as kernel, are described in:

 Documentation/devicetree/bindings/regulator/st,stpmic1-regulator.txt 

3.3.2 SCMI Version[edit]

The PMIC can also be accessed via SCMI protocol. If this option is chosen, U-BOOT does not instantiate any STPMIC1 driver but instead it uses SCMI regulators to control power supplies.

3.4 Support in Cortex-A7 Secure[edit]

3.4.1 TF-A[edit]

STPMIC1 is used by TF-A firmware to:

  • Configure DDR power supplies.
  • Configure the regulators for system suspend and system shutdown.

Driver source code:

 include/drivers/st/stpmic1.h  
 drivers/st/pmic/stpmic1.c  

SPTMIC1 driver supports configuration via device-tree, bindings are described in:

 docs/devicetree/bindings/power/st,stpmic1.txt 

An example of PMIC configuration with device tree can be found in this file, node &i2c4:

 fdts/stm32mp15xx-edx.dtsi 

When using a PMIC on a board, TF-A is configured to use a secure I²C (I2C4 or I2C6). By default on STMicroelectronics boards, I2C4 is used.


Using another I²C (non-secure) is not supported in the TF-A implementation made by STMicroelectronics. But it is possible to modify the code and device tree files to support it.

Here is an example with I2C2:

  • Copy the chosen I²C node from Linux device tree in the TF-A device tree file for your board, as well as its dependencies (like pinctrl). You can also remove the properties not used by TF-A as done in the example below
/ {
...
	soc {
	...
 +		i2c2: i2c@40013000 {
 +			compatible = "st,stm32mp15-i2c";
 +			reg = <0x40013000 0x400>;
 +			clocks = <&rcc I2C2_K>;
 +			resets = <&rcc I2C2_R>;
 +			#address-cells = <1>;
 +			#size-cells = <0>;
 +			status = "disabled";
 +		};
  • change pmic node parent to this newly added I²C
& i2c2 {
	...
	pmic: stpmic@33 {   # You may also require to change this I²C address (33)
	...
};
  • remove in PMIC node the property:
secure-status = "okay";
#define I2C2_BASE			U(0x40013000)
	case UART7_BASE:
	case UART8_BASE:
	case IWDG2_BASE:
+	case I2C2_BASE:
		/* Allow drivers to register some non secure resources */
		VERBOSE("IO for non secure resource 0x%x\n",
			(unsigned int)base);
+	_CLK_SC_SELEC(RCC_MP_APB1ENSETR, 22, I2C2_K, _I2C12_SEL),
  • Regarding the GPIO ports used by I2C2: in this stm32mp1_clk_gate[] table, remove the #ifdef IMAGE_BL2 around GPIO banks entries if present

3.4.2 OP-TEE[edit]

STPMIC1 is used by OP-TEE OS to configure the regulators for system suspend and system shutdown.

Driver source code:

 core/include/drivers/stpmic1.h  
 core/drivers/stpmic1.c 
3.4.2.1 SCMI Driver[edit]

As most of regulators handled by OP-TEE, the STPMIC1 regulators can be shared via SCMI voltage domains protocol to the non secure world.