How to configure PWR Wake-up pins

Applicable for

STM32MP13x lines

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1. Purpose

This article describes the configuration of the PWR wake-up pins for a usage in Linux.
The PWR Wake-up pins are used to wake-up from Standby from an external device.
This article does not describe how to configure a wake-up pin to use it internally in OPTEE.

2. Overview

Wake-up pins overview

• Button: one external device plugged to a wake-up pin. Could also be a PMIC.
• PWR: PWR internal peripheral
• OPTEE PWR IRQ driver: driver in charge of PWR peripheral that provides access to the wake-up pin via an interrupts interface.
• OPTEE PWR IRQ user driver: PWR IRQ consumer used to enable one wake-up pin and forward events as notifications to the non-secure world.
• OPTEE notification: stack in charge of communication with the non secure world.
• Linux Linaro optee driver: stack in charge of communication with secure world. Transform OPTEE notifications to interrupts.
• GPIO keys: Linux driver using a wake-up pin handled by OPTEE. Could be any driver able to handle Linux interrupts.

3. Wake-up pin configuration

3.1. OPTEE configuration

Wake-up pins are configured in OPTEE via device-tree. A pwr-irq-user can be instantiated to handle the desired wake-up pin and send a OPTEE notification to Linux in case of event.

3.2. Linux configuration

Linux does not handle wake-up pin, but it can handle an OPTEE notification as an interrupt. This is configured via device-tree.

4. Example with wake-up pin 2

In the example below, the wake-up pin number 2 is configured by OPTEE, forwarded as notification number 4 to Linux, and used by "gpio-keys" driver in Linux to generate a key-press.

OPTEE device tree:

   wakeup_button: wakeup-button {
       compatible = "st,stm32mp1,pwr-irq-user";
       st,wakeup-pin-number = <2>;
       st,notif-it-id = <4>;
       status = "okay";
   };

Linux device tree:

       wake_up {
               compatible = "gpio-keys";
               status = "okay";
               
               button {
                       label = "wake-up";
                       linux,code = <KEY_WAKEUP>;
                       interrupts-extended = <&optee 4>;
                       status = "okay";
               };
       };