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| -rw-r--r-- | docs/specs/acpi_hw_reduced_hotplug.rst | 70 | ||||
| -rw-r--r-- | docs/specs/index.rst | 1 |
2 files changed, 71 insertions, 0 deletions
diff --git a/docs/specs/acpi_hw_reduced_hotplug.rst b/docs/specs/acpi_hw_reduced_hotplug.rst new file mode 100644 index 0000000000..911a98255b --- /dev/null +++ b/docs/specs/acpi_hw_reduced_hotplug.rst @@ -0,0 +1,70 @@ +================================================== +QEMU and ACPI BIOS Generic Event Device interface +================================================== + +The ACPI *Generic Event Device* (GED) is a HW reduced platform +specific device introduced in ACPI v6.1 that handles all platform +events, including the hotplug ones. GED is modelled as a device +in the namespace with a _HID defined to be ACPI0013. This document +describes the interface between QEMU and the ACPI BIOS. + +GED allows HW reduced platforms to handle interrupts in ACPI ASL +statements. It follows a very similar approach to the _EVT method +from GPIO events. All interrupts are listed in _CRS and the handler +is written in _EVT method. However, the QEMU implementation uses a +single interrupt for the GED device, relying on an IO memory region +to communicate the type of device affected by the interrupt. This way, +we can support up to 32 events with a unique interrupt. + +**Here is an example,** + +:: + + Device (\_SB.GED) + { + Name (_HID, "ACPI0013") + Name (_UID, Zero) + Name (_CRS, ResourceTemplate () + { + Interrupt (ResourceConsumer, Edge, ActiveHigh, Exclusive, ,, ) + { + 0x00000029, + } + }) + OperationRegion (EREG, SystemMemory, 0x09080000, 0x04) + Field (EREG, DWordAcc, NoLock, WriteAsZeros) + { + ESEL, 32 + } + Method (_EVT, 1, Serialized) + { + Local0 = ESEL // ESEL = IO memory region which specifies the + // device type. + If (((Local0 & One) == One)) + { + MethodEvent1() + } + If ((Local0 & 0x2) == 0x2) + { + MethodEvent2() + } + ... + } + } + +GED IO interface (4 byte access) +-------------------------------- +**read access:** + +:: + + [0x0-0x3] Event selector bit field (32 bit) set by QEMU. + + bits: + 0: Memory hotplug event + 1: System power down event + 2-31: Reserved + +**write_access:** + +Nothing is expected to be written into GED IO memory diff --git a/docs/specs/index.rst b/docs/specs/index.rst index 40adb97c5e..984ba44029 100644 --- a/docs/specs/index.rst +++ b/docs/specs/index.rst @@ -12,3 +12,4 @@ Contents: ppc-xive ppc-spapr-xive + acpi_hw_reduced_hotplug |