Documents basic concepts of ACPI Generic Event device(GED)
and interface between QEMU and the ACPI BIOS.
Signed-off-by: Shameer Kolothum <shameerali.kolothum.th...@huawei.com>
Reviewed-by: Eric Auger <eric.au...@redhat.com>
---
docs/specs/acpi_hw_reduced_hotplug.txt | 60 ++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
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diff --git a/docs/specs/acpi_hw_reduced_hotplug.txt
b/docs/specs/acpi_hw_reduced_hotplug.txt
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+QEMU<->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 like the _EVT method
+from GPIO events. All interrupts are listed in _CRS and the handler
+is written in _EVT method. However, Qemu implementation uses a single
+interrupt for the GED device, relying on 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
--
2.17.1
