MDIO bus and PHYs in ACPI

The PHYs on an MDIO bus [1] are probed and registered using fwnode_mdiobus_register_phy(). Later, for connecting these PHYs to MAC, the PHYs registered on the mdiobus have to be referenced.

UUID given below should be used as mentioned in the “Device Properties UUID For _DSD” [2] document.

• UUID: daffd814-6eba-4d8c-8a91-bc9bbf4aa301

This document introduces two _DSD properties that are to be used for PHYs on the MDIO bus.[3]

phy-handle

For each MAC node, a device property “phy-handle” is used to reference the PHY that is registered on an MDIO bus. This is mandatory for network interfaces that have PHYs connected to MAC via MDIO bus.

During the MDIO bus driver initialization, PHYs on this bus are probed using the _ADR object as shown below and are registered on the mdio bus.

::

Scope(_SB.MDI0) {

Device(PHY1) {

Name (_ADR, 0x1)

} // end of PHY1

Device(PHY2) {

Name (_ADR, 0x2)

} // end of PHY2

}

Later, during the MAC driver initialization, the registered PHY devices have to be retrieved from the mdio bus. For this, MAC driver needs reference to the previously registered PHYs which are provided using reference to the device as {_SB.MDI0.PHY1}.

phy-mode

The “phy-mode” _DSD property is used to describe the connection to the PHY. The valid values for “phy-mode” are defined in [4].

An ASL example of this is shown below.

DSDT entry for MDIO node

The MDIO bus has an SoC component(mdio controller) and a platform component(PHYs on the mdiobus).

a) Silicon Component This node describes the MDIO controller,MDI0 ——————————————–

Scope(_SB)
{
  Device(MDI0) {
    Name(_HID, "NXP0006")
    Name(_CCA, 1)
    Name(_UID, 0)
    Name(_CRS, ResourceTemplate() {
      Memory32Fixed(ReadWrite, MDI0_BASE, MDI_LEN)
      Interrupt(ResourceConsumer, Level, ActiveHigh, Shared)
       {
         MDI0_IT
       }
    }) // end of _CRS for MDI0
  } // end of MDI0
}

b) Platform Component This node defines the PHYs that are connected to the MDIO bus, MDI0 ——————————————————————-

Scope(\_SB.MDI0)
{
  Device(PHY1) {
    Name (_ADR, 0x1)
  } // end of PHY1

  Device(PHY2) {
    Name (_ADR, 0x2)
  } // end of PHY2
}

Below are the MAC nodes where PHY nodes are referenced. phy-mode and phy-handle are used as explained earlier. ——————————————————

Scope(\_SB.MCE0.PR17)
{
  Name (_DSD, Package () {
     ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
         Package () {
             Package (2) {"phy-mode", "rgmii-id"},
             Package (2) {"phy-handle", \_SB.MDI0.PHY1}
      }
   })
}

Scope(\_SB.MCE0.PR18)
{
  Name (_DSD, Package () {
    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
        Package () {
            Package (2) {"phy-mode", "rgmii-id"},
            Package (2) {"phy-handle", \_SB.MDI0.PHY2}}
    }
  })
}

References

[1] PHY Abstraction Layer

[2] https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf

[3] _DSD Device Properties Usage Rules

[4] Documentation/devicetree/bindings/net/ethernet-controller.yaml