How is SUB_NRST generated in STM32MP157x-EV1 eval board?

According to the documentation of the EV1 eval board:

"The STM32MP157xAA3 also drives a sub system reset, SUB_NRST signal on PD10 IO, to the peripherals: USB Host Hub, MFX, Ethernet, and RGB_LTDC connector."

Is this signal generated automatically by the STM32MP157? Is it software controlled? If the latter, is this implemented in OpenSTLinux images by default?

Thanks,

Guillermo