Commit e86fba50 authored by Shameer Kolothum's avatar Shameer Kolothum Committed by Michael S. Tsirkin
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docs/specs: Add ACPI GED documentation 



Documents basic concepts of ACPI Generic Event device(GED)
and interface between QEMU and the ACPI BIOS.

Signed-off-by: default avatarShameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: default avatarEric Auger <eric.auger@redhat.com>
Message-Id: <20190918130633.4872-10-shameerali.kolothum.thodi@huawei.com>
Acked-by: default avatarPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 1962f31b

docs/specs/acpi_hw_reduced_hotplug.rst

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==================================================

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

docs/specs/index.rst

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@@ -12,3 +12,4 @@ Contents: 


   ppc-xive

   ppc-spapr-xive

   acpi_hw_reduced_hotplug