I've been trying to reduce power consumption of the STM32MP157C-DK2 board and have a very low power linux platform. But the power consumption seems somewhat agnostic of power rails and clock rates.
For example, I removed the LCD, I boot to u-boot, then use the u-boot interface to disable the HDMI, Audio, and 3.3V rails, I all IO set to high Independence inputs, expect the I2C connected to the PMIC and the UART connected to the STLink interface, and I clear the clocks to all but the I2C and UART peripherals, I'm measuring 200mA at 5V or 1 watt. If I change the MPU to run directly off of the HSE clock the current drops from 200mA to 190-195mA. Per the datasheet, there should be a MUCH larger current drop.
Per the datasheet Table 21, IDDCore with all peripherals disabled and the MPU running at 24 MHz, the current should be 51.5 mA. I still have the VCC and the DDR powered. If I disable DDR in u-boot (which causes u-boot to die) I measure 170 mA. So the DDR is only consuming roughly 20 mA when idle. That means most of my current is coming from VDDCore and VDD.
If I set bit 1 of register 0x10 in the PMIC (which powers down all rails) I see the current drop to 40 mA. There are two LEDs on in this mode. So that seems about right.
At this point, this "low power" MPU consumes about the same amount of power as an NVidia Jetson Nano in idle (1.2 watts). Something must be wrong with this dev kit or this part. Has anyone else seen issues like this?
Please be aware that our devkits ST32MP157C-DK2 and ST32MP157C-EV1 are not optimized to reach best low power target.
Details analyze of the board schematics probably help you to catch possible over conso sources .
Note that on ST32MP157C-EV1 you have possibility to measure VDD, VDDCORE, VDD_DDR independently in order to better identify over conso sources.
Please have a look to "AN5284 STM32MP1 Series system power consumption."
Hope it help,