UCSI Interface

EC must have the ability to interface with a discrete PD controller to negotiate power contracts/alt-modes with port partner

See the UCSI specification for commands that are required in all UCSI implementations.

USB-C Connector System Software Interface (UCSI) Driver - Windows drivers | Microsoft Learn

In addition to the commands marked as Required, Windows requires these commands:

• GET_ALTERNATE_MODES

• GET_CAM_SUPPORTED

• GET_PDOS

• SET_NOTIFICATION_ENABLE: The system or controller must support the following notifications within SET_NOTIFICATION_ENABLE:

  • Supported Provider Capabilities Change

  • Negotiated Power Level Change

• GET_CONNECTOR_STATUS: The system or controller must support these connector status changes within GET_CONNECTOR_STATUS:

  • Supported Provider Capabilities Change

  • Negotiated Power Level Change

UCSI ACPI Interface

Shared Mailbox Interface

The following table is the reserved memory structure that must be reserved and shared with the EC for communication. When using FF-A this memory region must be statically carved out and 4K aligned and directly accessible by secure world.

ACPI Definitions

Device(USBC) {
  Name(_HID,EISAID(“USBC000”))
  Name(_CID,EISAID(“PNP0CA0”))
  Name(_UID,1)
  Name(_DDN, “USB Type-C”)
  Name(_ADR,0x0)

  OperationRegion(USBC, SystemMemory, 0xFFFF0000, 0x30)
  Field(USBC,AnyAcc,Lock,Preserve)
  {
    // USB C Mailbox Interface
    VERS,16, // PPM-\>OPM Version
    RES, 16, // Reserved
    CCI, 32, // PPM-\>OPM CCI Indicator
    CTRL,64, // OPM-\>PPM Control Messages
    MSGI,128, // OPM-\>PPM Message In
    MSGO,128, // PPM-\>OPM Message Out
  }

  Method(_DSM,4,Serialized,0,UnknownObj, {BuffObj, IntObj,IntObj,PkgObj})
  {
    // Compare passed in UUID to Supported UUID
    If(LEqual(Arg0,ToUUID(“6f8398c2-7ca4-11e4-ad36-631042b5008f”)))
    {
      // Use FFA to send Notification event down to copy data to EC
      If(LEqual(\\_SB.FFA0.AVAL,One)) {
        CreateQwordField(BUFF,0,STAT) // Out – Status
        CreateField(BUFF,128,128,UUID) // UUID of service
        CreateByteField(BUFF,32, CMDD) // In – First byte of command
        CreateField(BUFF,288,384,FIFD) // Out – Msg data

        // Create UCSI Doorbell Event
        Store(0x0, CMDD) // UCSI set doorbell
        Store(ToUUID("65467f50-827f-4e4f-8770-dbf4c3f77f45"), UUID) // EC_SVC_UCSI
        Store(USBC, FIFD) // Copy output data
        Store(Store(BUFF, \_SB_.FFA0.FFAC), BUFF)

        If(LEqual(STAT,0x0) ) // Check FF-A successful?
        {
          Return (FIFD)
        }
      } // End AVAL
      Return(Zero)
    } // End UUID
  } // End DSM
}

The UCSI service is routed over FF-A using the EC_SVC_UCSI service UUID 65467f50-827f-4e4f-8770-dbf4c3f77f45. This is distinct from the UCSI _DSM selector 6f8398c2-7ca4-11e4-ad36-631042b5008f, which is the OS-standard argument the _DSM method matches on.

QEMU Test-Stub FF-A Transport

The normative interface above uses a statically carved-out, 4K-aligned shared-memory mailbox reachable from secure world. For deterministic integration testing under QEMU there is a simplified FF-A transport that carries the mailbox inline in the FF-A DIRECT_REQ2 register payload instead of a shared-memory region. This test transport is for the QEMU test stub only and does not replace the normative shared-memory ACPI interface described above.

Framing (routed to EC_SVC_UCSI, 65467f50-827f-4e4f-8770-dbf4c3f77f45):

• Request payload:
  • byte 0 = doorbell/command tag 0x00 (UCSI set doorbell).
  • byte offsets 1 through 48 inclusive = the full 48-byte mailbox (VERSION..MESSAGE OUT) copied inline.
  • remaining bytes = zero padding.
• Response payload:
  • byte offsets 0 through 47 inclusive = the updated 48-byte mailbox returned by the stub (VERSION, CCI, unchanged CONTROL, and populated MESSAGE IN).

Because the FF-A register payload comfortably holds the 49-byte request, no shared-memory carve-out or memory-retrieve mapping is required for the test stub.