The Apalis IMX8X datasheet mentions “LDO3OUT” should be set for the voltage for a 2nd Ethernet’s RGMII pins, but where do we set this? Is this a SCFW change or device tree change and do you have an example?
The secondary RGMII/RMII Ethernet interface needs special attention regarding the supply voltage level. The RGMII/RMII voltage is switchable through LDO3OUT of the PMIC PF8100. The voltage level must be defined by software configuration. During the power-up sequence, the IO voltage is set to 3.3V by default. All the RGMII/RMII signals are configured as GPIO inputs with enabled pulldown resistors. If the interface is used with 1.8V IO voltage, it is important to configure first the
LDO3OUT voltage and then change the alternate function to RGMII/RMII. This ensures full compatibility with 1.8V RGMII signal levels.
If the secondary Ethernet interface is used as RGMII, the output voltages are limited to 1.8V and 2.5V. For RMII and other alternate functions (e.g., GPIO) of these pins, also 3.3V logic level is suitable. Please note that the ENET1_MDC and ENET1_MDIO are always set to 3.3V, independent of the RGMII/RMII signals’ output voltage settings.