EC Input Management

An EC may have several input devices including LID, Power key, touch and keyboard. HID based devices requiring low latency input, are recommended to be connected directly through a non-secure BUS interface such as I2C or I3C for performance reasons.

LID State

Monitor sensors that indicate lid state. If lid is opened, potentially boot the system. If lid is closed, potentially shut down or hibernate the system.

ACPI Example for LID notificiation

Assuming that LID is managed by the EC during registration we register for Input Management service for a Virtual ID = 1

 Name(_DSD, Package() {
      ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), //Device Prop UUID
      Package() {
        Package(2) {
          "arm-arml0002-ffa-ntf-bind",
          Package() {
              1, // Revision
              1, // Count of following packages
              Package () {
                     ToUUID("e3168a99-4a57-4a2b-8c5e-11bcfec73406"), // Input Management UUID
                     Package () {
                          0x02,     // Cookie for LID
                      }
              },
         }
      }
    }
  }) // _DSD()

  Method(_DSM, 0x4, NotSerialized)
  {
    // Arg0 - UUID
    // Arg1 - Revision
    // Arg2: Function Index
    //         0 - Query
    //         1 - Notify
    //         2 - binding failure
    //         3 - infra failure    
    // Arg3 - Data
  
    //
    // Device specific method used to query
    // configuration data. See ACPI 5.0 specification
    // for further details.
    //
    If(LEqual(Arg0, Buffer(0x10) {
        //
        // UUID: {7681541E-8827-4239-8D9D-36BE7FE12542}
        //
        0x1e, 0x54, 0x81, 0x76, 0x27, 0x88, 0x39, 0x42, 0x8d, 0x9d, 0x36, 0xbe, 0x7f, 0xe1, 0x25, 0x42
      }))
    {
      // Query Function
      If(LEqual(Arg2, Zero)) 
      {
        Return(Buffer(One) { 0x03 }) // Bitmask Query + Notify
      }
      
      // Notify Function
      If(LEqual(Arg2, One))
      {
        // Arg3 - Package {UUID, Cookie}
        Local0 = DeRefOf(Index(Arg3,1))
        Switch(Local0) {
          Case(2) {
            Notify(\_SB._LID, 0x80)
          }
        }
      }
    }
    Return(Buffer(One) { 0x00 })
  }

System Wake Event

Ability to wake the system from various external events. This is for more complicated events that aren’t a simple GPIO for LID/Power button that require EC monitoring.

HID descriptor Interface

Communication with EC must have packet sent/received in HID format so the OS HIDClass driver can properly understand requests. At this time HID packets will go over HIDI2C but in future these HID packets could be included over a single interface.