BRK DT and “st,stm32prog-gpios”

[SylvainB]

Hi,

The u-boot dtsi in the repository (https://github.com/octavosystems/OSD32MP1-BRK-device-tree/blob/master/u-boot-v2020.01/stm32mp157c-osd32mp1-brk-u-boot.dtsi) contains the following config node:

config{
u-boot,boot-led = “LED2_GRN”;
u-boot,error-led = “LED2_RED”;
u-boot,mmc-env-partition = “ssbl”;
st,stm32prog-gpios = <&gpiod 9 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>;
};

I don’t understand the “stm32prog-gpios” property as the PD9 gpio does not seem to be connected to anything.
Moreover, I’m still able to stm32prog via DFU with this line is removed.

I have 2 questions:
Can I safely remove it ?
Can you, please, explain me when such a GPIO is needed ?

TIA,
Sylvain.

[Eshtaartha Basu]

Hello SylvainB,

Under “config” DT node of OSD32MP1-BRK, GPIO PD9 is being initialized as CubeProgrammerMode pin to be able to force STM32MP1 into Cube Programmer Mode if needed as described under section 1.1 here – https://wiki.st.com/stm32mpu/wiki/How_to_configure_U-Boot_for_your_board

1. Can I safely remove it ?
[Octavo]: Depends on your end application and how you’d prefer to load/update firmware whenever necessary.

2. Can you, please, explain me when such a GPIO is needed ?
[Octavo]: You can flash the uSD card of BRK using CubeProgrammer running on host PC (which supplies fsbl and ssbl over USB) after setting BRK’s boot pins to 0b000 but this process becomes laborious if you need to flash several devices on the run or provide updates to several devices regularly.

CubeProgrammerMode pin, when set, will help load FSBL and SSBL (U-Boot) directly from uSD card and put the device in DFU mode. U-Boot can be configured to grab the latest firmware (from predefined servers) and update the board suitably. This is how most of the OTA (Over The Air) updates take place.

[SylvainB]

Thank you Eshtaartha for this valuable information !

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