Re: [Qemu-arm] [PATCH-for-4.2 v9 10/12] docs/specs: Add ACPI GED documentation

[Auger Eric]

Hi Shameer,
On 8/13/19 11:05 PM, Shameer Kolothum wrote:
> Documents basic concepts of ACPI Generic Event device(GED)
> and interface between QEMU and the ACPI BIOS.
> 
> Signed-off-by: Shameer Kolothum <address@hidden>
Reviewed-by: Eric Auger <address@hidden>

Thanks

Eric
> ---
>  docs/specs/acpi_hw_reduced_hotplug.txt | 60 ++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
>  create mode 100644 docs/specs/acpi_hw_reduced_hotplug.txt
> 
> diff --git a/docs/specs/acpi_hw_reduced_hotplug.txt 
> b/docs/specs/acpi_hw_reduced_hotplug.txt
> new file mode 100644
> index 0000000000..46839be5ff
> --- /dev/null
> +++ b/docs/specs/acpi_hw_reduced_hotplug.txt
> @@ -0,0 +1,60 @@
> +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:
> +        1:  Memory hotplug event
> +        2:  System power down event
> +     3-31:  Reserved
> +
> +write_access:
> +    Nothing is expected to be written into GED IO memory
>