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+ACPI Tables
+-----------
+The expectations of individual ACPI tables are discussed in the list that
+follows.
+
+If a section number is used, it refers to a section number in the ACPI
+specification where the object is defined.  If "Signature Reserved" is used,
+the table signature (the first four bytes of the table) is the only portion
+of the table recognized by the specification, and the actual table is defined
+outside of the UEFI Forum (see Section 5.2.6 of the specification).
+
+For ACPI on arm64, tables also fall into the following categories:
+
+       -- Required: DSDT, FADT, GTDT, MADT, MCFG, RSDP, SPCR, XSDT
+
+       -- Recommended: BERT, EINJ, ERST, HEST, SSDT
+
+       -- Optional: BGRT, CPEP, CSRT, DRTM, ECDT, FACS, FPDT, MCHI, MPST,
+          MSCT, RASF, SBST, SLIT, SPMI, SRAT, TCPA, TPM2, UEFI
+
+       -- Not supported: BOOT, DBG2, DBGP, DMAR, ETDT, HPET, IBFT, IVRS,
+          LPIT, MSDM, RSDT, SLIC, WAET, WDAT, WDRT, WPBT
+
+
+Table  Usage for ARMv8 Linux
+-----  ----------------------------------------------------------------
+BERT   Section 18.3 (signature == "BERT")
+       == Boot Error Record Table ==
+       Must be supplied if RAS support is provided by the platform.  It
+       is recommended this table be supplied.
+
+BOOT   Signature Reserved (signature == "BOOT")
+       == simple BOOT flag table ==
+       Microsoft only table, will not be supported.
+
+BGRT   Section 5.2.22 (signature == "BGRT")
+       == Boot Graphics Resource Table ==
+       Optional, not currently supported, with no real use-case for an
+       ARM server.
+
+CPEP   Section 5.2.18 (signature == "CPEP")
+       == Corrected Platform Error Polling table ==
+       Optional, not currently supported, and not recommended until such
+       time as ARM-compatible hardware is available, and the specification
+       suitably modified.
+
+CSRT   Signature Reserved (signature == "CSRT")
+       == Core System Resources Table ==
+       Optional, not currently supported.
+
+DBG2   Signature Reserved (signature == "DBG2")
+       == DeBuG port table 2 ==
+       Microsoft only table, will not be supported.
+
+DBGP   Signature Reserved (signature == "DBGP")
+       == DeBuG Port table ==
+       Microsoft only table, will not be supported.
+
+DSDT   Section 5.2.11.1 (signature == "DSDT")
+       == Differentiated System Description Table ==
+       A DSDT is required; see also SSDT.
+
+       ACPI tables contain only one DSDT but can contain one or more SSDTs,
+       which are optional.  Each SSDT can only add to the ACPI namespace,
+       but cannot modify or replace anything in the DSDT.
+
+DMAR   Signature Reserved (signature == "DMAR")
+       == DMA Remapping table ==
+       x86 only table, will not be supported.
+
+DRTM   Signature Reserved (signature == "DRTM")
+       == Dynamic Root of Trust for Measurement table ==
+       Optional, not currently supported.
+
+ECDT   Section 5.2.16 (signature == "ECDT")
+       == Embedded Controller Description Table ==
+       Optional, not currently supported, but could be used on ARM if and
+       only if one uses the GPE_BIT field to represent an IRQ number, since
+       there are no GPE blocks defined in hardware reduced mode.  This would
+       need to be modified in the ACPI specification.
+
+EINJ   Section 18.6 (signature == "EINJ")
+       == Error Injection table ==
+       This table is very useful for testing platform response to error
+       conditions; it allows one to inject an error into the system as
+       if it had actually occurred.  However, this table should not be
+       shipped with a production system; it should be dynamically loaded
+       and executed with the ACPICA tools only during testing.
+
+ERST   Section 18.5 (signature == "ERST")
+       == Error Record Serialization Table ==
+       On a platform supports RAS, this table must be supplied if it is not
+       UEFI-based; if it is UEFI-based, this table may be supplied. When this
+       table is not present, UEFI run time service will be utilized to save
+       and retrieve hardware error information to and from a persistent store.
+
+ETDT   Signature Reserved (signature == "ETDT")
+       == Event Timer Description Table ==
+       Obsolete table, will not be supported.
+
+FACS   Section 5.2.10 (signature == "FACS")
+       == Firmware ACPI Control Structure ==
+       It is unlikely that this table will be terribly useful.  If it is
+       provided, the Global Lock will NOT be used since it is not part of
+       the hardware reduced profile, and only 64-bit address fields will
+       be considered valid.
+
+FADT   Section 5.2.9 (signature == "FACP")
+       == Fixed ACPI Description Table ==
+       Required for arm64.
+
+       The HW_REDUCED_ACPI flag must be set.  All of the fields that are
+       to be ignored when HW_REDUCED_ACPI is set are expected to be set to
+       zero.
+
+       If an FACS table is provided, the X_FIRMWARE_CTRL field is to be
+       used, not FIRMWARE_CTRL.
+
+       If PSCI is used (as is recommended), make sure that ARM_BOOT_ARCH is
+       filled in properly -- that the PSCI_COMPLIANT flag is set and that
+       PSCI_USE_HVC is set or unset as needed (see table 5-37).
+
+       For the DSDT that is also required, the X_DSDT field is to be used,
+       not the DSDT field.
+
+FPDT   Section 5.2.23 (signature == "FPDT")
+       == Firmware Performance Data Table ==
+       Optional, not currently supported.
+
+GTDT   Section 5.2.24 (signature == "GTDT")
+       == Generic Timer Description Table ==
+       Required for arm64.
+
+HEST   Section 18.3.2 (signature == "HEST")
+       == Hardware Error Source Table ==
+       Until further error source types are defined, use only types 6 (AER
+       Root Port), 7 (AER Endpoint), 8 (AER Bridge), or 9 (Generic Hardware
+       Error Source).  Firmware first error handling is possible if and only
+       if Trusted Firmware is being used on arm64.
+
+       Must be supplied if RAS support is provided by the platform.  It
+       is recommended this table be supplied.
+
+HPET   Signature Reserved (signature == "HPET")
+       == High Precision Event timer Table ==
+       x86 only table, will not be supported.
+
+IBFT   Signature Reserved (signature == "IBFT")
+       == iSCSI Boot Firmware Table ==
+       Microsoft defined table, support TBD.
+
+IVRS   Signature Reserved (signature == "IVRS")
+       == I/O Virtualization Reporting Structure ==
+       x86_64 (AMD) only table, will not be supported.
+
+LPIT   Signature Reserved (signature == "LPIT")
+       == Low Power Idle Table ==
+       x86 only table as of ACPI 5.1; future versions have been adapted for
+       use with ARM and will be recommended in order to support ACPI power
+       management.
+
+MADT   Section 5.2.12 (signature == "APIC")
+       == Multiple APIC Description Table ==
+       Required for arm64.  Only the GIC interrupt controller structures
+       should be used (types 0xA - 0xE).
+
+MCFG   Signature Reserved (signature == "MCFG")
+       == Memory-mapped ConFiGuration space ==
+       If the platform supports PCI/PCIe, an MCFG table is required.
+
+MCHI   Signature Reserved (signature == "MCHI")
+       == Management Controller Host Interface table ==
+       Optional, not currently supported.
+
+MPST   Section 5.2.21 (signature == "MPST")
+       == Memory Power State Table ==
+       Optional, not currently supported.
+
+MSDM   Signature Reserved (signature == "MSDM")
+       == Microsoft Data Management table ==
+       Microsoft only table, will not be supported.
+
+MSCT   Section 5.2.19 (signature == "MSCT")
+       == Maximum System Characteristic Table ==
+       Optional, not currently supported.
+
+RASF   Section 5.2.20 (signature == "RASF")
+       == RAS Feature table ==
+       Optional, not currently supported.
+
+RSDP   Section 5.2.5 (signature == "RSD PTR")
+       == Root System Description PoinTeR ==
+       Required for arm64.
+
+RSDT   Section 5.2.7 (signature == "RSDT")
+       == Root System Description Table ==
+       Since this table can only provide 32-bit addresses, it is deprecated
+       on arm64, and will not be used.
+
+SBST   Section 5.2.14 (signature == "SBST")
+       == Smart Battery Subsystem Table ==
+       Optional, not currently supported.
+
+SLIC   Signature Reserved (signature == "SLIC")
+       == Software LIcensing table ==
+       Microsoft only table, will not be supported.
+
+SLIT   Section 5.2.17 (signature == "SLIT")
+       == System Locality distance Information Table ==
+       Optional in general, but required for NUMA systems.
+
+SPCR   Signature Reserved (signature == "SPCR")
+       == Serial Port Console Redirection table ==
+       Required for arm64.
+
+SPMI   Signature Reserved (signature == "SPMI")
+       == Server Platform Management Interface table ==
+       Optional, not currently supported.
+
+SRAT   Section 5.2.16 (signature == "SRAT")
+       == System Resource Affinity Table ==
+       Optional, but if used, only the GICC Affinity structures are read.
+       To support NUMA, this table is required.
+
+SSDT   Section 5.2.11.2 (signature == "SSDT")
+       == Secondary System Description Table ==
+       These tables are a continuation of the DSDT; these are recommended
+       for use with devices that can be added to a running system, but can
+       also serve the purpose of dividing up device descriptions into more
+       manageable pieces.
+
+       An SSDT can only ADD to the ACPI namespace.  It cannot modify or
+       replace existing device descriptions already in the namespace.
+
+       These tables are optional, however.  ACPI tables should contain only
+       one DSDT but can contain many SSDTs.
+
+TCPA   Signature Reserved (signature == "TCPA")
+       == Trusted Computing Platform Alliance table ==
+       Optional, not currently supported, and may need changes to fully
+       interoperate with arm64.
+
+TPM2   Signature Reserved (signature == "TPM2")
+       == Trusted Platform Module 2 table ==
+       Optional, not currently supported, and may need changes to fully
+       interoperate with arm64.
+
+UEFI   Signature Reserved (signature == "UEFI")
+       == UEFI ACPI data table ==
+       Optional, not currently supported.  No known use case for arm64,
+       at present.
+
+WAET   Signature Reserved (signature == "WAET")
+       == Windows ACPI Emulated devices Table ==
+       Microsoft only table, will not be supported.
+
+WDAT   Signature Reserved (signature == "WDAT")
+       == Watch Dog Action Table ==
+       Microsoft only table, will not be supported.
+
+WDRT   Signature Reserved (signature == "WDRT")
+       == Watch Dog Resource Table ==
+       Microsoft only table, will not be supported.
+
+WPBT   Signature Reserved (signature == "WPBT")
+       == Windows Platform Binary Table ==
+       Microsoft only table, will not be supported.
+
+XSDT   Section 5.2.8 (signature == "XSDT")
+       == eXtended System Description Table ==
+       Required for arm64.
+
+
+ACPI Objects
+------------
+The expectations on individual ACPI objects are discussed in the list that
+follows:
+
+Name   Section         Usage for ARMv8 Linux
+----   ------------    -------------------------------------------------
+_ADR   6.1.1           Use as needed.
+
+_BBN   6.5.5           Use as needed; PCI-specific.
+
+_BDN   6.5.3           Optional; not likely to be used on arm64.
+
+_CCA   6.2.17          This method should be defined for all bus masters
+                       on arm64.  While cache coherency is assumed, making
+                       it explicit ensures the kernel will set up DMA as
+                       it should.
+
+_CDM   6.2.1           Optional, to be used only for processor devices.
+
+_CID   6.1.2           Use as needed.
+
+_CLS   6.1.3           Use as needed.
+
+_CRS   6.2.2           Required on arm64.
+
+_DCK   6.5.2           Optional; not likely to be used on arm64.
+
+_DDN   6.1.4           This field can be used for a device name.  However,
+                       it is meant for DOS device names (e.g., COM1), so be
+                       careful of its use across OSes.
+
+_DEP   6.5.8           Use as needed.
+
+_DIS   6.2.3           Optional, for power management use.
+
+_DLM   5.7.5           Optional.
+
+_DMA   6.2.4           Optional.
+
+_DSD   6.2.5           To be used with caution.  If this object is used, try
+                       to use it within the constraints already defined by the
+                       Device Properties UUID.  Only in rare circumstances
+                       should it be necessary to create a new _DSD UUID.
+
+                       In either case, submit the _DSD definition along with
+                       any driver patches for discussion, especially when
+                       device properties are used.  A driver will not be
+                       considered complete without a corresponding _DSD
+                       description.  Once approved by kernel maintainers,
+                       the UUID or device properties must then be registered
+                       with the UEFI Forum; this may cause some iteration as
+                       more than one OS will be registering entries.
+
+_DSM                   Do not use this method.  It is not standardized, the
+                       return values are not well documented, and it is
+                       currently a frequent source of error.
+
+_DSW   7.2.1           Use as needed; power management specific.
+
+_EDL   6.3.1           Optional.
+
+_EJD   6.3.2           Optional.
+
+_EJx   6.3.3           Optional.
+
+_FIX   6.2.7           x86 specific, not used on arm64.
+
+\_GL   5.7.1           This object is not to be used in hardware reduced
+                       mode, and therefore should not be used on arm64.
+
+_GLK   6.5.7           This object requires a global lock be defined; there
+                       is no global lock on arm64 since it runs in hardware
+                       reduced mode.  Hence, do not use this object on arm64.
+
+\_GPE  5.3.1           This namespace is for x86 use only.  Do not use it
+                       on arm64.
+
+_GSB   6.2.7           Optional.
+
+_HID   6.1.5           Use as needed.  This is the primary object to use in
+                       device probing, though _CID and _CLS may also be used.
+
+_HPP   6.2.8           Optional, PCI specific.
+
+_HPX   6.2.9           Optional, PCI specific.
+
+_HRV   6.1.6           Optional, use as needed to clarify device behavior; in
+                       some cases, this may be easier to use than _DSD.
+
+_INI   6.5.1           Not required, but can be useful in setting up devices
+                       when UEFI leaves them in a state that may not be what
+                       the driver expects before it starts probing.
+
+_IRC   7.2.15          Use as needed; power management specific.
+
+_LCK   6.3.4           Optional.
+
+_MAT   6.2.10          Optional; see also the MADT.
+
+_MLS   6.1.7           Optional, but highly recommended for use in
+                       internationalization.
+
+_OFF   7.1.2           It is recommended to define this method for any device
+                       that can be turned on or off.
+
+_ON    7.1.3           It is recommended to define this method for any device
+                       that can be turned on or off.
+
+\_OS   5.7.3           This method will return "Linux" by default (this is
+                       the value of the macro ACPI_OS_NAME on Linux).  The
+                       command line parameter acpi_os=<string> can be used
+                       to set it to some other value.
+
+_OSC   6.2.11          This method can be a global method in ACPI (i.e.,
+                       \_SB._OSC), or it may be associated with a specific
+                       device (e.g., \_SB.DEV0._OSC), or both.  When used
+                       as a global method, only capabilities published in
+                       the ACPI specification are allowed.  When used as
+                       a device-specific method, the process described for
+                       using _DSD MUST be used to create an _OSC definition;
+                       out-of-process use of _OSC is not allowed.  That is,
+                       submit the device-specific _OSC usage description as
+                       part of the kernel driver submission, get it approved
+                       by the kernel community, then register it with the
+                       UEFI Forum.
+
+\_OSI  5.7.2           Deprecated on ARM64.  Any invocation of this method
+                       will print a warning on the console and return false.
+                       That is, as far as ACPI firmware is concerned, _OSI
+                       cannot be used to determine what sort of system is
+                       being used or what functionality is provided.  The
+                       _OSC method is to be used instead.
+
+_OST   6.3.5           Optional.
+
+_PDC   8.4.1           Deprecated, do not use on arm64.
+
+\_PIC  5.8.1           The method should not be used.  On arm64, the only
+                       interrupt model available is GIC.
+
+_PLD   6.1.8           Optional.
+
+\_PR   5.3.1           This namespace is for x86 use only on legacy systems.
+                       Do not use it on arm64.
+
+_PRS   6.2.12          Optional.
+
+_PRT   6.2.13          Required as part of the definition of all PCI root
+                       devices.
+
+_PRW   7.2.13          Use as needed; power management specific.
+
+_PRx   7.2.8-11        Use as needed; power management specific.  If _PR0 is
+                       defined, _PR3 must also be defined.
+
+_PSC   7.2.6           Use as needed; power management specific.
+
+_PSE   7.2.7           Use as needed; power management specific.
+
+_PSW   7.2.14          Use as needed; power management specific.
+
+_PSx   7.2.2-5         Use as needed; power management specific.  If _PS0 is
+                       defined, _PS3 must also be defined.  If clocks or
+                       regulators need adjusting to be consistent with power
+                       usage, change them in these methods.
+
+\_PTS  7.3.1           Use as needed; power management specific.
+
+_PXM   6.2.14          Optional.
+
+_REG   6.5.4           Use as needed.
+
+\_REV  5.7.4           Always returns the latest version of ACPI supported.
+
+_RMV   6.3.6           Optional.
+
+\_SB   5.3.1           Required on arm64; all devices must be defined in this
+                       namespace.
+
+_SEG   6.5.6           Use as needed; PCI-specific.
+
+\_SI   5.3.1,          Optional.
+       9.1
+
+_SLI   6.2.15          Optional; recommended when SLIT table is in use.
+
+_STA   6.3.7,          It is recommended to define this method for any device
+       7.1.4           that can be turned on or off.
+
+_SRS   6.2.16          Optional; see also _PRS.
+
+_STR   6.1.10          Recommended for conveying device names to end users;
+                       this is preferred over using _DDN.
+
+_SUB   6.1.9           Use as needed; _HID or _CID are preferred.
+
+_SUN   6.1.11          Optional.
+
+\_Sx   7.3.2           Use as needed; power management specific.
+
+_SxD   7.2.16-19       Use as needed; power management specific.
+
+_SxW   7.2.20-24       Use as needed; power management specific.
+
+_SWS   7.3.3           Use as needed; power management specific; this may
+                       require specification changes for use on arm64.
+
+\_TTS  7.3.4           Use as needed; power management specific.
+
+\_TZ   5.3.1           Optional.
+
+_UID   6.1.12          Recommended for distinguishing devices of the same
+                       class; define it if at all possible.
+
+\_WAK  7.3.5           Use as needed; power management specific.
+
+
+ACPI Event Model
+----------------
+Do not use GPE block devices; these are not supported in the hardware reduced
+profile used by arm64.  Since there are no GPE blocks defined for use on ARM
+platforms, GPIO-signaled interrupts should be used for creating system events.
+
+
+ACPI Processor Control
+----------------------
+Section 8 of the ACPI specification is currently undergoing change that
+should be completed in the 6.0 version of the specification.  Processor
+performance control will be handled differently for arm64 at that point
+in time.  Processor aggregator devices (section 8.5) will not be used,
+for example, but another similar mechanism instead.
+
+While UEFI constrains what we can say until the release of 6.0, it is
+recommended that CPPC (8.4.5) be used as the primary model.  This will
+still be useful into the future.  C-states and P-states will still be
+provided, but most of the current design work appears to favor CPPC.
+
+Further, it is essential that the ARMv8 SoC provide a fully functional
+implementation of PSCI; this will be the only mechanism supported by ACPI
+to control CPU power state (including secondary CPU booting).
+
+More details will be provided on the release of the ACPI 6.0 specification.
+
+
+ACPI System Address Map Interfaces
+----------------------------------
+In Section 15 of the ACPI specification, several methods are mentioned as
+possible mechanisms for conveying memory resource information to the kernel.
+For arm64, we will only support UEFI for booting with ACPI, hence the UEFI
+GetMemoryMap() boot service is the only mechanism that will be used.
+
+
+ACPI Platform Error Interfaces (APEI)
+-------------------------------------
+The APEI tables supported are described above.
+
+APEI requires the equivalent of an SCI and an NMI on ARMv8.  The SCI is used
+to notify the OSPM of errors that have occurred but can be corrected and the
+system can continue correct operation, even if possibly degraded.  The NMI is
+used to indicate fatal errors that cannot be corrected, and require immediate
+attention.
+
+Since there is no direct equivalent of the x86 SCI or NMI, arm64 handles
+these slightly differently.  The SCI is handled as a normal GPIO-signaled
+interrupt; given that these are corrected (or correctable) errors being
+reported, this is sufficient.  The NMI is emulated as the highest priority
+GPIO-signaled interrupt possible.  This implies some caution must be used
+since there could be interrupts at higher privilege levels or even interrupts
+at the same priority as the emulated NMI.  In Linux, this should not be the
+case but one should be aware it could happen.
+
+
+ACPI Objects Not Supported on ARM64
+-----------------------------------
+While this may change in the future, there are several classes of objects
+that can be defined, but are not currently of general interest to ARM servers.
+
+These are not supported:
+
+       -- Section 9.2: ambient light sensor devices
+
+       -- Section 9.3: battery devices
+
+       -- Section 9.4: lids (e.g., laptop lids)
+
+       -- Section 9.8.2: IDE controllers
+
+       -- Section 9.9: floppy controllers
+
+       -- Section 9.10: GPE block devices
+
+       -- Section 9.15: PC/AT RTC/CMOS devices
+
+       -- Section 9.16: user presence detection devices
+
+       -- Section 9.17: I/O APIC devices; all GICs must be enumerable via MADT
+
+       -- Section 9.18: time and alarm devices (see 9.15)
+
+
+ACPI Objects Not Yet Implemented
+--------------------------------
+While these objects have x86 equivalents, and they do make some sense in ARM
+servers, there is either no hardware available at present, or in some cases
+there may not yet be a non-ARM implementation.  Hence, they are currently not
+implemented though that may change in the future.
+
+Not yet implemented are:
+
+       -- Section 10: power source and power meter devices
+
+       -- Section 11: thermal management
+
+       -- Section 12: embedded controllers interface
+
+       -- Section 13: SMBus interfaces
+
+       -- Section 17: NUMA support (prototypes have been submitted for
+          review)