What pullup resistor to use for MDIO/MDC?

For MDIO & MDC (the serial management interface for Ethernet PHYs), you typically use a 1.5kΩ or 2.2kΩ pullup resistor to 3.3V or 2.5V, depending on the PHY’s I/O voltage level. Use one pull-up resistor per pin

However, you must still check your PHY manufacturer’s datasheet for the exact recommended value, as it may vary slightly between different PHYs and different IO voltages

• Texas Instruments typically uses a 2.2kΩ pullup for newer PHYs on both MDIO and MDC to VIO (which is typically 3.3V or 2.5V), but for older PHYs such as the DP83848 they recommended 1.5kΩ pullups.
• Microchip (formerly Micrel & SMSC) PHYs often recommend 1.5kΩ pullups to VIO, e.g. LAN8720A schematic checklist

Source:

• DP83TD510E datasheet, pin functions table: 2.2...4.0kΩ pullup on MDIO and MDC to VIO (typically 3.3V or 2.5V)
• DP83825I datasheet, section 6.3.11 Serial Management Interface: 2.2kΩ pullup on MDIO and MDC to VIO (typically 3.3V or 2.5V). Please note that the Pin functions table says can be added implying optionality, but section 6.3.11 makes it clear that they are required for proper operation.
• LAN8720A schematic checklist
• DP83848-EP datasheet, section 6.3.11 Serial Management Interface: 1.5kΩ pullup on MDIO and MDC to VIO (typically 3.3V or 2.5V)