71 lines
2.0 KiB
ReStructuredText
71 lines
2.0 KiB
ReStructuredText
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==================================================
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QEMU and ACPI BIOS Generic Event Device interface
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==================================================
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The ACPI *Generic Event Device* (GED) is a HW reduced platform
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specific device introduced in ACPI v6.1 that handles all platform
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events, including the hotplug ones. GED is modelled as a device
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in the namespace with a _HID defined to be ACPI0013. This document
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describes the interface between QEMU and the ACPI BIOS.
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GED allows HW reduced platforms to handle interrupts in ACPI ASL
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statements. It follows a very similar approach to the _EVT method
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from GPIO events. All interrupts are listed in _CRS and the handler
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is written in _EVT method. However, the QEMU implementation uses a
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single interrupt for the GED device, relying on an IO memory region
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to communicate the type of device affected by the interrupt. This way,
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we can support up to 32 events with a unique interrupt.
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**Here is an example,**
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::
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Device (\_SB.GED)
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{
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Name (_HID, "ACPI0013")
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Name (_UID, Zero)
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Name (_CRS, ResourceTemplate ()
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{
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Interrupt (ResourceConsumer, Edge, ActiveHigh, Exclusive, ,, )
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{
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0x00000029,
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}
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})
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OperationRegion (EREG, SystemMemory, 0x09080000, 0x04)
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Field (EREG, DWordAcc, NoLock, WriteAsZeros)
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{
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ESEL, 32
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}
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Method (_EVT, 1, Serialized)
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{
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Local0 = ESEL // ESEL = IO memory region which specifies the
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// device type.
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If (((Local0 & One) == One))
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{
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MethodEvent1()
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}
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If ((Local0 & 0x2) == 0x2)
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{
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MethodEvent2()
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}
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...
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}
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}
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GED IO interface (4 byte access)
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--------------------------------
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**read access:**
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::
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[0x0-0x3] Event selector bit field (32 bit) set by QEMU.
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bits:
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0: Memory hotplug event
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1: System power down event
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2-31: Reserved
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**write_access:**
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Nothing is expected to be written into GED IO memory
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