How do I modify HSLVEN_ETH bit or PRODUCT_BELOW_2V5 for example? Do I need to write source code or is this picked up in some device tree setting or regulator reading?

Hi @user_ABCD​ ,

Sorry for late reply.

Once you set PRODUCT_BELOW_2V5 OTP, HSLVEN bits are managed in TF-A with control of the actual VDD value.

See plat/st/stm32mp1/stm32mp1_syscfg.c - stm32mp1_syscfg_init(void) - line 104 ->132

Olivier