Regulator overview

Revision as of 15:52, 30 January 2023 by Registered User
Applicable for STM32MP13x lines, STM32MP15x lines

This article gives information about the Linux® regulator framework.

1. Article Purpose[edit source]

This article aims to explain how to use regulators:

  • how to configure a regulator on a Linux BSP
  • how to access a regulator from a kernel space

This article is applicable for the Linux kernel version 4.10 and later.

2. System overview[edit source]

Some documentation on the Linux regulator framework is provided with the kernel source code:overview.rst [1]

2.1. Overview[edit source]

The power supplies can be provided by various blocks:

  • External single regulators:
    • Low-dropout regulators (LDO)
    • BUCKs (DC-to-DC power converter)
    • Switches
  • A Power Management Integrated Circuit (PMIC) that integrates several LDO and BUCKS
  • Internal regulators from the microprocessor device internal blocks:
    • PWR peripheral [2]
    • VREFBUF peripheral [3]

All the regulators are implemented and controlled under the standard Linux regulator framework.

2.2. Components Description[edit source]


2.2.1. External devices: external regulators, PMIC[edit source]

This corresponds to physical components that provide the various power supplies on the board.

2.2.2. Microprocessor device internal regulators[edit source]

This corresponds to the regulators integrated to the microprocessor device. Those regulators supply mainly the USB and ADC peripherals.

2.2.3. Regulator drivers[edit source]

A regulator that can be controlled (enable/disable, adjust voltage...) needs a driver to operate. This is the role of the regulator driver.

A driver can also send notifications like over current or over temperature.


  • The kernel contains generic drivers for GPIO controlled regulators.
  • The PMIC uses a specific driver.
  • The internal regulators of the microprocessor device are implemented in the STM32 machine.
  • kernel Documentation regulator.txt [4]

2.2.4. Regulator framework core[edit source]

The core manages all the regulators. A consumer request is not handled directly by a regulator driver. It is handled by the core that can arbitrate requests between consumers in order to save power.

2.2.5. Regulator consumers[edit source]

The devices correspond to internal or external peripherals of the microprocessor device ( ADC, SDCARD, USB, ETHERNET... )

Each peripheral that needs a power supply to operate must enable it. When a regulator is not used, it is disabled by the core.

The consumer interface allows to control a regulator (enable/disable, set voltage...), and to register to a notification service.

  • kernel Documentation consumer.txt [5]

2.2.6. Sysfs interface[edit source]

The regulator framework offers a sysfs interface that can be used for monitoring. It is not possible to control a regulator via the sysfs.

2.2.7. Configfs interface[edit source]

Most of the regulator configurations are described in the device-tree (configfs)

3. How to find the source code[edit source]

Everything is part of the kernel source code:

  • The regulator framework core and drivers code are located in drivers/regulator directory

4. Regulator configuration[edit source]

4.1. Kernel configuration[edit source]

The configuration is done using the standard menuconfig. Most configurations are available under Device Drivers / Voltage and Current Regulator Support

4.2. Device tree configuration[edit source]

The device tree describes regulators and consumers:

  • A regulator provides a supply.
  • A consumer uses a supply.

When possible, the supply name comes from the electrical schematics of the board.

4.2.1. Some regulator drivers[edit source]

Binding Doc:regulator.yaml Gpio controlled regulator[edit source]

usb otg vbus:

   vbus_otg: regulator-vbus_otg {
       compatible = "regulator-fixed";
       regulator-name = "vbus_otg";
       regulator-min-microvolt = <5000000>;
       regulator-max-microvolt = <5000000>;
       gpio = <&gpioz 4 0>;

Binding Doc:fixed-regulator.yaml

sdcard level shifter:

   sd_switch: regulator-sd_switch {
       compatible = "regulator-gpio";
       regulator-name = "sd_switch";
       regulator-min-microvolt = <1800000>;
       regulator-max-microvolt = <2900000>;
       regulator-type = "voltage";
       gpios = <&gpiof 14 GPIO_ACTIVE_HIGH>;
       gpios-states = <0>;
       states = <1800000 0x1 2900000 0x0>;

Binding Doc:gpio-regulator.yaml PMIC[edit source]
   pmic: stpmu1@33 {
       compatible = "st,stpmu1";
       reg = <0x33>;
       interrupts = <0 2>;
       interrupt-parent = <&gpioa>;
       #interrupt-cells = <2>;
       status = "okay";
       regulators {
           compatible = "st,stpmu1-regulators";
           vddcore: buck1 {
               regulator-compatible = "buck1";
               regulator-name = "vddcore";
               regulator-min-microvolt = <800000>;
               regulator-max-microvolt = <1350000>;
               regulator-initial-mode = <2>;
           vdd_ddr: buck2 {
               regulator-compatible = "buck2";
               regulator-name = "vdd_ddr";
               regulator-min-microvolt = <1350000>;
               regulator-max-microvolt = <1350000>;
               regulator-initial-mode = <2>;
       }; Microcontroller device internal regulator[edit source]

VREFBUF[3] regulator:

   vrefbuf: vrefbuf@50025000 {
       compatible = "st,stm32-vrefbuf";
       reg = <0x50025000 0x8>;
       regulator-min-microvolt = <1500000>;
       regulator-max-microvolt = <2500000>;
       clocks = <&rcc_clk VREF>;
       status = "disabled";

Binding Doc:st,stm32-vrefbuf.yaml SCMI regulator[edit source]

The SCMI protocol permits to drive a regulator handled by the secure monitor (OP-TEE). Linux scmi driver implements requests like get, set voltage, enable and disable. OP-TEE then receives and arbitrate the requests depending on internal constraints.

 scmi0_voltd: protocol@17 {
 	reg = <0x17>;
 	scmi0_regu: regulators {
 		scmi_reg11: voltd-reg11 {
 			voltd-name = "reg11";
 			regulator-name = "reg11";
 		scmi_reg18: voltd-reg18 {
 			voltd-name = "reg18";
 			regulator-name = "reg18";

Binding Doc:arm,scmi.yaml

4.2.2. Consumers[edit source]

See below some examples of consumers.

The SDMMC needs 2 power supply:

   &sdmmc1 {
       vmmc-supply = <&vdd_sd>;
       vqmmc-supply = <&sd_switch>;

The name before "-supply" is not free. vmmc and vqmmc are imposed by the consumer driver. They should be aligned with the name used in the data sheet of the driven component.

The USBPHY is supplied by vdd_usb:

   &usbphyc {
       vdd-supply = <&vdd_usb>;

The DAC is supplied by vdda:

   &dac {
       pinctrl-names = "default";
       pinctrl-0 = <&dac_ch1_pins &dac_ch2_pins>;
       vref-supply = <&vdda>;
       status = "okay";

The regulators can be consumers. This is used to define power domains:

   pmic: stpmu1@33 {
       compatible = "st,stpmu1";
       regulators {
           compatible = "st,stpmu1-regulators";
           ldo1-supply = <&v3v3>;
           ldo2-supply = <&v3v3>;
           ldo5-supply = <&v3v3>;
           ldo6-supply = <&v3v3>;
           vref_ddr-supply = <&vdd_ddr>;
           vbus_otg-supply = <&bst_out>;
           sw_out-supply = <&bst_out>;

Enabling ldo1 will enable v3v3 automatically.

5. Power management[edit source]

The regulator framework handles the power management at runtime and during suspend.

5.1. Runtime[edit source]

  • The consumers should disable the regulators that are not needed.
  • The core disables a regulator as soon as it is not requested by any consumer.

This can be avoided by the usage of "regulator-always-on" property in the device-tree.

5.2. Suspend[edit source]

The regulator framework offers the possibility to define suspend states for regulators. This is only possible if the driver allows it. The regulator suspend sate is no more handled by the linux kernel in OpenSTLinux distribution.

regulator-state-standby, regulator-state-mem, regulator-state-disk are used to define the state of the regulators during suspend.

               regulator-state-standby {
                   regulator-suspend-microvolt = <900000>;
                   regulator-mode = <8>;
               regulator-state-mem {

  • The regulator runtime strategy does not apply to suspend. With "regulator-on-in-suspend", the regulator is enabled in suspend even if no consumer uses it.
  • "regulator-always-on" does not apply to suspend states.

6. How to trace and debug the framework[edit source]

6.1. How to trace[edit source]

The regulator framework provides debugfs tools. The most important one is regulator/regulator_summary:

 cat /sys/kernel/debug/regulator/regulator_summary 
 regulator                      use open bypass voltage current     min     max
  regulator-dummy                  0    6      0     0mV     0mA     0mV     0mV 
     vddcore                       0    0      0  1200mV     0mA   800mV  1350mV 
     vdd_ddr                       0    1      0  1350mV     0mA  1350mV  1350mV 
        vtt_ddr                    0    0      0   675mV     0mA   675mV   675mV 
     vdd                           0    1      0  3300mV     0mA  3300mV  3300mV 
        58007000.sdmmc                                            3300mV  3300mV
     v3v3                          1    5      0  3300mV     0mA  3300mV  3300mV 
        58007000.sdmmc                                            3300mV  3300mV
        vdda                       0    2      0  2900mV     0mA  2900mV  2900mV 
           40017000.dac                                              0mV     0mV
           48003000.adc                                              0mV     0mV
        v2v8                       0    0      0  2800mV     0mA  2800mV  2800mV 
        vdd_sd                     0    1      0  2900mV     0mA  2900mV  2900mV 
           58005000.sdmmc                                         2900mV  2900mV
        v1v8                       0    0      0  1800mV     0mA  1800mV  1800mV 
     vdd_usb                       0    0      0  3300mV     0mA  3300mV  3300mV 
     bst_out                       0    2      0  5000mV     0mA     0mV     0mV 
        vbus_otg                   0    0      0  5000mV     0mA     0mV     0mV 
        vbus_sw                    0    0      0  5000mV     0mA     0mV     0mV 
  sd_switch                        0    1      0  2900mV     0mA  1800mV  2900mV 
     58005000.sdmmc                                               2700mV  2900mV
  reg11                            0    0      0  1100mV     0mA  1100mV  1100mV 
  reg18                            0    0      0  1800mV     0mA  1800mV  1800mV 
  usb33                            0    0      0  3300mV     0mA  3300mV  3300mV 
  vref_ddr                         0    0      0   675mV     0mA     0mV     0mV 


  • use: counts the "enable" calls made by the consumers
  • open: is the number of consumers that get the regulator
  • vdd_sd is a consumer for v3v3
  • 58005000.sdmmc is a consumer for v3v3, vdd_sd, sd_switch
  • when regulator_always_on property is set, use is equal to ZERO (but the regulator is enabled...)

7. References[edit source]