Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 809 insertions, 0 deletions

diff --git a/Documentation/arch/arm64/acpi_object_usage.rst b/Documentation/arch/arm64/acpi_object_usage.rst
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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, PCCT, SSDT
+
+       -  Optional: AGDI, BGRT, CEDT, CPEP, CSRT, DBG2, DRTM, ECDT, FACS, FPDT,
+          HMAT, IBFT, IORT, MCHI, MPAM, MPST, MSCT, NFIT, PMTT, PPTT, RASF, SBST,
+          SDEI, SLIT, SPMI, SRAT, STAO, TCPA, TPM2, UEFI, XENV
+
+       -  Not supported: AEST, APMT, BOOT, DBGP, DMAR, ETDT, HPET, IVRS, LPIT,
+          MSDM, OEMx, PDTT, PSDT, RAS2, RSDT, SLIC, WAET, WDAT, WDRT, WPBT
+
+====== ========================================================================
+Table  Usage for ARMv8 Linux
+====== ========================================================================
+AEST   Signature Reserved (signature == "AEST")
+
+       **Arm Error Source Table**
+
+       This table informs the OS of any error nodes in the system that are
+       compliant with the Arm RAS architecture.
+
+AGDI   Signature Reserved (signature == "AGDI")
+
+       **Arm Generic diagnostic Dump and Reset Device Interface Table**
+
+       This table describes a non-maskable event, that is used by the platform
+       firmware, to request the OS to generate a diagnostic dump and reset the device.
+
+APMT   Signature Reserved (signature == "APMT")
+
+       **Arm Performance Monitoring Table**
+
+       This table describes the properties of PMU support implemented by
+       components in the system.
+
+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.
+
+CEDT   Signature Reserved (signature == "CEDT")
+
+       **CXL Early Discovery Table**
+
+       This table allows the OS to discover any CXL Host Bridges and the Host
+       Bridge registers.
+
+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**
+
+       License has changed and should be usable.  Optional if used instead
+       of earlycon=<device> on the command line.
+
+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, useful for boot performance profiling.
+
+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**
+
+       ARM-specific error sources have been defined; please use those or the
+       PCI types such as type 6 (AER Root Port), 7 (AER Endpoint), or 8 (AER
+       Bridge), or use type 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.
+
+HMAT   Section 5.2.28 (signature == "HMAT")
+
+       **Heterogeneous Memory Attribute Table**
+
+       This table describes the memory attributes, such as memory side cache
+       attributes and bandwidth and latency details, related to Memory Proximity
+       Domains. The OS uses this information to optimize the system memory
+       configuration.
+
+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.
+
+IORT   Signature Reserved (signature == "IORT")
+
+       **Input Output Remapping Table**
+
+       arm64 only table, required in order to describe IO topology, SMMUs,
+       and GIC ITSs, and how those various components are connected together,
+       such as identifying which components are behind which SMMUs/ITSs.
+       This table will only be required on certain SBSA platforms (e.g.,
+       when using GICv3-ITS and an SMMU); on SBSA Level 0 platforms, it
+       remains optional.
+
+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; starting with ACPI 6.0, processor
+       descriptions and power states on ARM platforms should use the DSDT
+       and define processor container devices (_HID ACPI0010, Section 8.4,
+       and more specifically 8.4.3 and 8.4.4).
+
+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 - 0xF).
+
+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.
+
+MPAM   Signature Reserved (signature == "MPAM")
+
+       **Memory Partitioning And Monitoring table**
+
+       This table allows the OS to discover the MPAM controls implemented by
+       the subsystems.
+
+MPST   Section 5.2.21 (signature == "MPST")
+
+       **Memory Power State Table**
+
+       Optional, not currently supported.
+
+MSCT   Section 5.2.19 (signature == "MSCT")
+
+       **Maximum System Characteristic Table**
+
+       Optional, not currently supported.
+
+MSDM   Signature Reserved (signature == "MSDM")
+
+       **Microsoft Data Management table**
+
+       Microsoft only table, will not be supported.
+
+NFIT   Section 5.2.25 (signature == "NFIT")
+
+       **NVDIMM Firmware Interface Table**
+
+       Optional, not currently supported.
+
+OEMx   Signature of "OEMx" only
+
+       **OEM Specific Tables**
+
+       All tables starting with a signature of "OEM" are reserved for OEM
+       use.  Since these are not meant to be of general use but are limited
+       to very specific end users, they are not recommended for use and are
+       not supported by the kernel for arm64.
+
+PCCT   Section 14.1 (signature == "PCCT)
+
+       **Platform Communications Channel Table**
+
+       Recommend for use on arm64; use of PCC is recommended when using CPPC
+       to control performance and power for platform processors.
+
+PDTT   Section 5.2.29 (signature == "PDTT")
+
+       **Platform Debug Trigger Table**
+
+       This table describes PCC channels used to gather debug logs of
+       non-architectural features.
+
+
+PMTT   Section 5.2.21.12 (signature == "PMTT")
+
+       **Platform Memory Topology Table**
+
+       Optional, not currently supported.
+
+PPTT   Section 5.2.30 (signature == "PPTT")
+
+       **Processor Properties Topology Table**
+
+       This table provides the processor and cache topology.
+
+PSDT   Section 5.2.11.3 (signature == "PSDT")
+
+       **Persistent System Description Table**
+
+       Obsolete table, will not be supported.
+
+RAS2   Section 5.2.21 (signature == "RAS2")
+
+       **RAS Features 2 table**
+
+       This table provides interfaces for the RAS capabilities implemented in
+       the platform.
+
+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.  If provided, it will be ignored.
+
+SBST   Section 5.2.14 (signature == "SBST")
+
+       **Smart Battery Subsystem Table**
+
+       Optional, not currently supported.
+
+SDEI   Signature Reserved (signature == "SDEI")
+
+       **Software Delegated Exception Interface table**
+
+       This table advertises the presence of the SDEI interface.
+
+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 arm64 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.
+
+STAO   Signature Reserved (signature == "STAO")
+
+       **_STA Override table**
+
+       Optional, but only necessary in virtualized environments in order to
+       hide devices from guest OSs.
+
+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.
+
+XENV   Signature Reserved (signature == "XENV")
+
+       **Xen project table**
+
+       Optional, used only by Xen at present.
+
+XSDT   Section 5.2.8 (signature == "XSDT")
+
+       **eXtended System Description Table**
+
+       Required for arm64.
+====== ========================================================================
+
+ACPI Objects
+------------
+The expectations on individual ACPI objects that are likely to be used are
+shown in the list that follows; any object not explicitly mentioned below
+should be used as needed for a particular platform or particular subsystem,
+such as power management or PCI.
+
+===== ================ ========================================================
+Name   Section         Usage for ARMv8 Linux
+===== ================ ========================================================
+_CCA   6.2.17          This method must be defined for all bus masters
+                       on arm64 - there are no assumptions made about
+                       whether such devices are cache coherent or not.
+                       The _CCA value is inherited by all descendants of
+                       these devices so it does not need to be repeated.
+                       Without _CCA on arm64, the kernel does not know what
+                       to do about setting up DMA for the device.
+
+                       NB: this method provides default cache coherency
+                       attributes; the presence of an SMMU can be used to
+                       modify that, however.  For example, a master could
+                       default to non-coherent, but be made coherent with
+                       the appropriate SMMU configuration (see Table 17 of
+                       the IORT specification, ARM Document DEN 0049B).
+
+_CID   6.1.2           Use as needed, see also _HID.
+
+_CLS   6.1.3           Use as needed, see also _HID.
+
+_CPC   8.4.7.1         Use as needed, power management specific.  CPPC is
+                       recommended on arm64.
+
+_CRS   6.2.2           Required on arm64.
+
+_CSD   8.4.2.2         Use as needed, used only in conjunction with _CST.
+
+_CST   8.4.2.1         Low power idle states (8.4.4) are recommended instead
+                       of C-states.
+
+_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.
+
+_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   9.1.1           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.
+
+\_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.
+
+_HID   6.1.5           This is the primary object to use in device probing,
+		       though _CID and _CLS may also be used.
+
+_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.
+
+_LPI   8.4.4.3         Recommended for use with processor definitions (_HID
+		       ACPI0010) on arm64.  See also _RDI.
+
+_MLS   6.1.7           Highly recommended for use in internationalization.
+
+_OFF   7.2.2           It is recommended to define this method for any device
+                       that can be turned on or off.
+
+_ON    7.2.3           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.  As far as ACPI firmware is
+		       concerned, _OSI is not to be used to determine what
+		       sort of system is being used or what functionality
+		       is provided.  The _OSC method is to be used instead.
+
+_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.
+
+\_PR   5.3.1           This namespace is for x86 use only on legacy systems.
+                       Do not use it on arm64.
+
+_PRT   6.2.13          Required as part of the definition of all PCI root
+                       devices.
+
+_PRx   7.3.8-11        Use as needed; power management specific.  If _PR0 is
+                       defined, _PR3 must also be defined.
+
+_PSx   7.3.2-5         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.
+
+_RDI   8.4.4.4         Recommended for use with processor definitions (_HID
+		       ACPI0010) on arm64.  This should only be used in
+		       conjunction with _LPI.
+
+\_REV  5.7.4           Always returns the latest version of ACPI supported.
+
+\_SB   5.3.1           Required on arm64; all devices must be defined in this
+                       namespace.
+
+_SLI   6.2.15          Use is recommended when SLIT table is in use.
+
+_STA   6.3.7,          It is recommended to define this method for any device
+       7.2.4           that can be turned on or off.  See also the STAO table
+                       that provides overrides to hide devices in virtualized
+                       environments.
+
+_SRS   6.2.16          Use as needed; 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          Use as needed, but recommended.
+
+_SWS   7.4.3           Use as needed; power management specific; this may
+                       require specification changes for use on arm64.
+
+_UID   6.1.12          Recommended for distinguishing devices of the same
+                       class; define it if at all possible.
+===== ================ ========================================================
+
+
+
+
+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, ACPI events must be signaled differently.
+
+There are two options: GPIO-signaled interrupts (Section 5.6.5), and
+interrupt-signaled events (Section 5.6.9).  Interrupt-signaled events are a
+new feature in the ACPI 6.1 specification.  Either - or both - can be used
+on a given platform, and which to use may be dependent of limitations in any
+given SoC.  If possible, interrupt-signaled events are recommended.
+
+
+ACPI Processor Control
+----------------------
+Section 8 of the ACPI specification changed significantly in version 6.0.
+Processors should now be defined as Device objects with _HID ACPI0007; do
+not use the deprecated Processor statement in ASL.  All multiprocessor systems
+should also define a hierarchy of processors, done with Processor Container
+Devices (see Section 8.4.3.1, _HID ACPI0010); do not use processor aggregator
+devices (Section 8.5) to describe processor topology.  Section 8.4 of the
+specification describes the semantics of these object definitions and how
+they interrelate.
+
+Most importantly, the processor hierarchy defined also defines the low power
+idle states that are available to the platform, along with the rules for
+determining which processors can be turned on or off and the circumstances
+that control that.  Without this information, the processors will run in
+whatever power state they were left in by UEFI.
+
+Note too, that the processor Device objects defined and the entries in the
+MADT for GICs are expected to be in synchronization.  The _UID of the Device
+object must correspond to processor IDs used in the MADT.
+
+It is recommended that CPPC (8.4.5) be used as the primary model for processor
+performance control on arm64.  C-states and P-states may become available at
+some point in the future, but most 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.  Booting of secondary CPUs using the ACPI
+parking protocol is possible, but discouraged, since only PSCI is supported
+for ARM servers.
+
+
+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 high priority interrupt;
+given that these are corrected (or correctable) errors being reported, this
+is sufficient.  The NMI is emulated as the highest priority 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.
+Some of these objects have x86 equivalents, and may actually make sense in ARM
+servers.  However, there is either no hardware available at present, or there
+may not even be a non-ARM implementation yet.  Hence, they are not currently
+supported.
+
+The following classes of objects 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)
+
+       -  Section 10: power source and power meter devices
+
+       -  Section 11: thermal management
+
+       -  Section 12: embedded controllers interface
+
+       -  Section 13: SMBus interfaces
+
+
+This also means that there is no support for the following objects:
+
+====   =========================== ====   ==========
+Name   Section                     Name   Section
+====   =========================== ====   ==========
+_ALC   9.3.4                       _FDM   9.10.3
+_ALI   9.3.2                       _FIX   6.2.7
+_ALP   9.3.6                       _GAI   10.4.5
+_ALR   9.3.5                       _GHL   10.4.7
+_ALT   9.3.3                       _GTM   9.9.2.1.1
+_BCT   10.2.2.10                   _LID   9.5.1
+_BDN   6.5.3                       _PAI   10.4.4
+_BIF   10.2.2.1                    _PCL   10.3.2
+_BIX   10.2.2.1                    _PIF   10.3.3
+_BLT   9.2.3                       _PMC   10.4.1
+_BMA   10.2.2.4                    _PMD   10.4.8
+_BMC   10.2.2.12                   _PMM   10.4.3
+_BMD   10.2.2.11                   _PRL   10.3.4
+_BMS   10.2.2.5                    _PSR   10.3.1
+_BST   10.2.2.6                    _PTP   10.4.2
+_BTH   10.2.2.7                    _SBS   10.1.3
+_BTM   10.2.2.9                    _SHL   10.4.6
+_BTP   10.2.2.8                    _STM   9.9.2.1.1
+_DCK   6.5.2                       _UPD   9.16.1
+_EC    12.12                       _UPP   9.16.2
+_FDE   9.10.1                      _WPC   10.5.2
+_FDI   9.10.2                      _WPP   10.5.3
+====   =========================== ====   ==========