| 1 | ================================================== |
| 2 | QEMU and ACPI BIOS Generic Event Device interface |
| 3 | ================================================== |
| 4 | |
| 5 | The ACPI *Generic Event Device* (GED) is a HW reduced platform |
| 6 | specific device introduced in ACPI v6.1 that handles all platform |
| 7 | events, including the hotplug ones. GED is modelled as a device |
| 8 | in the namespace with a _HID defined to be ACPI0013. This document |
| 9 | describes the interface between QEMU and the ACPI BIOS. |
| 10 | |
| 11 | GED allows HW reduced platforms to handle interrupts in ACPI ASL |
| 12 | statements. It follows a very similar approach to the _EVT method |
| 13 | from GPIO events. All interrupts are listed in _CRS and the handler |
| 14 | is written in _EVT method. However, the QEMU implementation uses a |
| 15 | single interrupt for the GED device, relying on an IO memory region |
| 16 | to communicate the type of device affected by the interrupt. This way, |
| 17 | we can support up to 32 events with a unique interrupt. |
| 18 | |
| 19 | **Here is an example,** |
| 20 | |
| 21 | :: |
| 22 | |
| 23 | Device (\_SB.GED) |
| 24 | { |
| 25 | Name (_HID, "ACPI0013") |
| 26 | Name (_UID, Zero) |
| 27 | Name (_CRS, ResourceTemplate () |
| 28 | { |
| 29 | Interrupt (ResourceConsumer, Edge, ActiveHigh, Exclusive, ,, ) |
| 30 | { |
| 31 | 0x00000029, |
| 32 | } |
| 33 | }) |
| 34 | OperationRegion (EREG, SystemMemory, 0x09080000, 0x04) |
| 35 | Field (EREG, DWordAcc, NoLock, WriteAsZeros) |
| 36 | { |
| 37 | ESEL, 32 |
| 38 | } |
| 39 | Method (_EVT, 1, Serialized) |
| 40 | { |
| 41 | Local0 = ESEL // ESEL = IO memory region which specifies the |
| 42 | // device type. |
| 43 | If (((Local0 & One) == One)) |
| 44 | { |
| 45 | MethodEvent1() |
| 46 | } |
| 47 | If ((Local0 & 0x2) == 0x2) |
| 48 | { |
| 49 | MethodEvent2() |
| 50 | } |
| 51 | ... |
| 52 | } |
| 53 | } |
| 54 | |
| 55 | GED IO interface (4 byte access) |
| 56 | -------------------------------- |
| 57 | **read access:** |
| 58 | |
| 59 | :: |
| 60 | |
| 61 | [0x0-0x3] Event selector bit field (32 bit) set by QEMU. |
| 62 | |
| 63 | bits: |
| 64 | 0: Memory hotplug event |
| 65 | 1: System power down event |
| 66 | 2: NVDIMM hotplug event |
| 67 | 3: CPU hotplug event |
| 68 | 4-31: Reserved |
| 69 | |
| 70 | **write_access:** |
| 71 | |
| 72 | Nothing is expected to be written into GED IO memory |