Documentation/arm64/acpi_object_usage.rst

   1 ===========
   2 ACPI Tables
   3 ===========
   4
   5 The expectations of individual ACPI tables are discussed in the list that
   6 follows.
   7
   8 If a section number is used, it refers to a section number in the ACPI
   9 specification where the object is defined.  If "Signature Reserved" is used,
  10 the table signature (the first four bytes of the table) is the only portion
  11 of the table recognized by the specification, and the actual table is defined
  12 outside of the UEFI Forum (see Section 5.2.6 of the specification).
  13
  14 For ACPI on arm64, tables also fall into the following categories:
  15
  16        -  Required: DSDT, FADT, GTDT, MADT, MCFG, RSDP, SPCR, XSDT
  17
  18        -  Recommended: BERT, EINJ, ERST, HEST, PCCT, SSDT
  19
  20        -  Optional: BGRT, CPEP, CSRT, DBG2, DRTM, ECDT, FACS, FPDT, IORT,
  21           MCHI, MPST, MSCT, NFIT, PMTT, RASF, SBST, SLIT, SPMI, SRAT, STAO,
  22           TCPA, TPM2, UEFI, XENV
  23
  24        -  Not supported: BOOT, DBGP, DMAR, ETDT, HPET, IBFT, IVRS, LPIT,
  25           MSDM, OEMx, PSDT, RSDT, SLIC, WAET, WDAT, WDRT, WPBT
  26
  27 ====== ========================================================================
  28 Table  Usage for ARMv8 Linux
  29 ====== ========================================================================
  30 BERT   Section 18.3 (signature == "BERT")
  31
  32        **Boot Error Record Table**
  33
  34        Must be supplied if RAS support is provided by the platform.  It
  35        is recommended this table be supplied.
  36
  37 BOOT   Signature Reserved (signature == "BOOT")
  38
  39        **simple BOOT flag table**
  40
  41        Microsoft only table, will not be supported.
  42
  43 BGRT   Section 5.2.22 (signature == "BGRT")
  44
  45        **Boot Graphics Resource Table**
  46
  47        Optional, not currently supported, with no real use-case for an
  48        ARM server.
  49
  50 CPEP   Section 5.2.18 (signature == "CPEP")
  51
  52        **Corrected Platform Error Polling table**
  53
  54        Optional, not currently supported, and not recommended until such
  55        time as ARM-compatible hardware is available, and the specification
  56        suitably modified.
  57
  58 CSRT   Signature Reserved (signature == "CSRT")
  59
  60        **Core System Resources Table**
  61
  62        Optional, not currently supported.
  63
  64 DBG2   Signature Reserved (signature == "DBG2")
  65
  66        **DeBuG port table 2**
  67
  68        License has changed and should be usable.  Optional if used instead
  69        of earlycon=<device> on the command line.
  70
  71 DBGP   Signature Reserved (signature == "DBGP")
  72
  73        **DeBuG Port table**
  74
  75        Microsoft only table, will not be supported.
  76
  77 DSDT   Section 5.2.11.1 (signature == "DSDT")
  78
  79        **Differentiated System Description Table**
  80
  81        A DSDT is required; see also SSDT.
  82
  83        ACPI tables contain only one DSDT but can contain one or more SSDTs,
  84        which are optional.  Each SSDT can only add to the ACPI namespace,
  85        but cannot modify or replace anything in the DSDT.
  86
  87 DMAR   Signature Reserved (signature == "DMAR")
  88
  89        **DMA Remapping table**
  90
  91        x86 only table, will not be supported.
  92
  93 DRTM   Signature Reserved (signature == "DRTM")
  94
  95        **Dynamic Root of Trust for Measurement table**
  96
  97        Optional, not currently supported.
  98
  99 ECDT   Section 5.2.16 (signature == "ECDT")
 100
 101        **Embedded Controller Description Table**
 102
 103        Optional, not currently supported, but could be used on ARM if and
 104        only if one uses the GPE_BIT field to represent an IRQ number, since
 105        there are no GPE blocks defined in hardware reduced mode.  This would
 106        need to be modified in the ACPI specification.
 107
 108 EINJ   Section 18.6 (signature == "EINJ")
 109
 110        **Error Injection table**
 111
 112        This table is very useful for testing platform response to error
 113        conditions; it allows one to inject an error into the system as
 114        if it had actually occurred.  However, this table should not be
 115        shipped with a production system; it should be dynamically loaded
 116        and executed with the ACPICA tools only during testing.
 117
 118 ERST   Section 18.5 (signature == "ERST")
 119
 120        **Error Record Serialization Table**
 121
 122        On a platform supports RAS, this table must be supplied if it is not
 123        UEFI-based; if it is UEFI-based, this table may be supplied. When this
 124        table is not present, UEFI run time service will be utilized to save
 125        and retrieve hardware error information to and from a persistent store.
 126
 127 ETDT   Signature Reserved (signature == "ETDT")
 128
 129        **Event Timer Description Table**
 130
 131        Obsolete table, will not be supported.
 132
 133 FACS   Section 5.2.10 (signature == "FACS")
 134
 135        **Firmware ACPI Control Structure**
 136
 137        It is unlikely that this table will be terribly useful.  If it is
 138        provided, the Global Lock will NOT be used since it is not part of
 139        the hardware reduced profile, and only 64-bit address fields will
 140        be considered valid.
 141
 142 FADT   Section 5.2.9 (signature == "FACP")
 143
 144        **Fixed ACPI Description Table**
 145        Required for arm64.
 146
 147
 148        The HW_REDUCED_ACPI flag must be set.  All of the fields that are
 149        to be ignored when HW_REDUCED_ACPI is set are expected to be set to
 150        zero.
 151
 152        If an FACS table is provided, the X_FIRMWARE_CTRL field is to be
 153        used, not FIRMWARE_CTRL.
 154
 155        If PSCI is used (as is recommended), make sure that ARM_BOOT_ARCH is
 156        filled in properly - that the PSCI_COMPLIANT flag is set and that
 157        PSCI_USE_HVC is set or unset as needed (see table 5-37).
 158
 159        For the DSDT that is also required, the X_DSDT field is to be used,
 160        not the DSDT field.
 161
 162 FPDT   Section 5.2.23 (signature == "FPDT")
 163
 164        **Firmware Performance Data Table**
 165
 166        Optional, not currently supported.
 167
 168 GTDT   Section 5.2.24 (signature == "GTDT")
 169
 170        **Generic Timer Description Table**
 171
 172        Required for arm64.
 173
 174 HEST   Section 18.3.2 (signature == "HEST")
 175
 176        **Hardware Error Source Table**
 177
 178        ARM-specific error sources have been defined; please use those or the
 179        PCI types such as type 6 (AER Root Port), 7 (AER Endpoint), or 8 (AER
 180        Bridge), or use type 9 (Generic Hardware Error Source).  Firmware first
 181        error handling is possible if and only if Trusted Firmware is being
 182        used on arm64.
 183
 184        Must be supplied if RAS support is provided by the platform.  It
 185        is recommended this table be supplied.
 186
 187 HPET   Signature Reserved (signature == "HPET")
 188
 189        **High Precision Event timer Table**
 190
 191        x86 only table, will not be supported.
 192
 193 IBFT   Signature Reserved (signature == "IBFT")
 194
 195        **iSCSI Boot Firmware Table**
 196
 197        Microsoft defined table, support TBD.
 198
 199 IORT   Signature Reserved (signature == "IORT")
 200
 201        **Input Output Remapping Table**
 202
 203        arm64 only table, required in order to describe IO topology, SMMUs,
 204        and GIC ITSs, and how those various components are connected together,
 205        such as identifying which components are behind which SMMUs/ITSs.
 206        This table will only be required on certain SBSA platforms (e.g.,
 207        when using GICv3-ITS and an SMMU); on SBSA Level 0 platforms, it
 208        remains optional.
 209
 210 IVRS   Signature Reserved (signature == "IVRS")
 211
 212        **I/O Virtualization Reporting Structure**
 213
 214        x86_64 (AMD) only table, will not be supported.
 215
 216 LPIT   Signature Reserved (signature == "LPIT")
 217
 218        **Low Power Idle Table**
 219
 220        x86 only table as of ACPI 5.1; starting with ACPI 6.0, processor
 221        descriptions and power states on ARM platforms should use the DSDT
 222        and define processor container devices (_HID ACPI0010, Section 8.4,
 223        and more specifically 8.4.3 and 8.4.4).
 224
 225 MADT   Section 5.2.12 (signature == "APIC")
 226
 227        **Multiple APIC Description Table**
 228
 229        Required for arm64.  Only the GIC interrupt controller structures
 230        should be used (types 0xA - 0xF).
 231
 232 MCFG   Signature Reserved (signature == "MCFG")
 233
 234        **Memory-mapped ConFiGuration space**
 235
 236        If the platform supports PCI/PCIe, an MCFG table is required.
 237
 238 MCHI   Signature Reserved (signature == "MCHI")
 239
 240        **Management Controller Host Interface table**
 241
 242        Optional, not currently supported.
 243
 244 MPST   Section 5.2.21 (signature == "MPST")
 245
 246        **Memory Power State Table**
 247
 248        Optional, not currently supported.
 249
 250 MSCT   Section 5.2.19 (signature == "MSCT")
 251
 252        **Maximum System Characteristic Table**
 253
 254        Optional, not currently supported.
 255
 256 MSDM   Signature Reserved (signature == "MSDM")
 257
 258        **Microsoft Data Management table**
 259
 260        Microsoft only table, will not be supported.
 261
 262 NFIT   Section 5.2.25 (signature == "NFIT")
 263
 264        **NVDIMM Firmware Interface Table**
 265
 266        Optional, not currently supported.
 267
 268 OEMx   Signature of "OEMx" only
 269
 270        **OEM Specific Tables**
 271
 272        All tables starting with a signature of "OEM" are reserved for OEM
 273        use.  Since these are not meant to be of general use but are limited
 274        to very specific end users, they are not recommended for use and are
 275        not supported by the kernel for arm64.
 276
 277 PCCT   Section 14.1 (signature == "PCCT)
 278
 279        **Platform Communications Channel Table**
 280
 281        Recommend for use on arm64; use of PCC is recommended when using CPPC
 282        to control performance and power for platform processors.
 283
 284 PMTT   Section 5.2.21.12 (signature == "PMTT")
 285
 286        **Platform Memory Topology Table**
 287
 288        Optional, not currently supported.
 289
 290 PSDT   Section 5.2.11.3 (signature == "PSDT")
 291
 292        **Persistent System Description Table**
 293
 294        Obsolete table, will not be supported.
 295
 296 RASF   Section 5.2.20 (signature == "RASF")
 297
 298        **RAS Feature table**
 299
 300        Optional, not currently supported.
 301
 302 RSDP   Section 5.2.5 (signature == "RSD PTR")
 303
 304        **Root System Description PoinTeR**
 305
 306        Required for arm64.
 307
 308 RSDT   Section 5.2.7 (signature == "RSDT")
 309
 310        **Root System Description Table**
 311
 312        Since this table can only provide 32-bit addresses, it is deprecated
 313        on arm64, and will not be used.  If provided, it will be ignored.
 314
 315 SBST   Section 5.2.14 (signature == "SBST")
 316
 317        **Smart Battery Subsystem Table**
 318
 319        Optional, not currently supported.
 320
 321 SLIC   Signature Reserved (signature == "SLIC")
 322
 323        **Software LIcensing table**
 324
 325        Microsoft only table, will not be supported.
 326
 327 SLIT   Section 5.2.17 (signature == "SLIT")
 328
 329        **System Locality distance Information Table**
 330
 331        Optional in general, but required for NUMA systems.
 332
 333 SPCR   Signature Reserved (signature == "SPCR")
 334
 335        **Serial Port Console Redirection table**
 336
 337        Required for arm64.
 338
 339 SPMI   Signature Reserved (signature == "SPMI")
 340
 341        **Server Platform Management Interface table**
 342
 343        Optional, not currently supported.
 344
 345 SRAT   Section 5.2.16 (signature == "SRAT")
 346
 347        **System Resource Affinity Table**
 348
 349        Optional, but if used, only the GICC Affinity structures are read.
 350        To support arm64 NUMA, this table is required.
 351
 352 SSDT   Section 5.2.11.2 (signature == "SSDT")
 353
 354        **Secondary System Description Table**
 355
 356        These tables are a continuation of the DSDT; these are recommended
 357        for use with devices that can be added to a running system, but can
 358        also serve the purpose of dividing up device descriptions into more
 359        manageable pieces.
 360
 361        An SSDT can only ADD to the ACPI namespace.  It cannot modify or
 362        replace existing device descriptions already in the namespace.
 363
 364        These tables are optional, however.  ACPI tables should contain only
 365        one DSDT but can contain many SSDTs.
 366
 367 STAO   Signature Reserved (signature == "STAO")
 368
 369        **_STA Override table**
 370
 371        Optional, but only necessary in virtualized environments in order to
 372        hide devices from guest OSs.
 373
 374 TCPA   Signature Reserved (signature == "TCPA")
 375
 376        **Trusted Computing Platform Alliance table**
 377
 378        Optional, not currently supported, and may need changes to fully
 379        interoperate with arm64.
 380
 381 TPM2   Signature Reserved (signature == "TPM2")
 382
 383        **Trusted Platform Module 2 table**
 384
 385        Optional, not currently supported, and may need changes to fully
 386        interoperate with arm64.
 387
 388 UEFI   Signature Reserved (signature == "UEFI")
 389
 390        **UEFI ACPI data table**
 391
 392        Optional, not currently supported.  No known use case for arm64,
 393        at present.
 394
 395 WAET   Signature Reserved (signature == "WAET")
 396
 397        **Windows ACPI Emulated devices Table**
 398
 399        Microsoft only table, will not be supported.
 400
 401 WDAT   Signature Reserved (signature == "WDAT")
 402
 403        **Watch Dog Action Table**
 404
 405        Microsoft only table, will not be supported.
 406
 407 WDRT   Signature Reserved (signature == "WDRT")
 408
 409        **Watch Dog Resource Table**
 410
 411        Microsoft only table, will not be supported.
 412
 413 WPBT   Signature Reserved (signature == "WPBT")
 414
 415        **Windows Platform Binary Table**
 416
 417        Microsoft only table, will not be supported.
 418
 419 XENV   Signature Reserved (signature == "XENV")
 420
 421        **Xen project table**
 422
 423        Optional, used only by Xen at present.
 424
 425 XSDT   Section 5.2.8 (signature == "XSDT")
 426
 427        **eXtended System Description Table**
 428
 429        Required for arm64.
 430 ====== ========================================================================
 431
 432 ACPI Objects
 433 ------------
 434 The expectations on individual ACPI objects that are likely to be used are
 435 shown in the list that follows; any object not explicitly mentioned below
 436 should be used as needed for a particular platform or particular subsystem,
 437 such as power management or PCI.
 438
 439 ===== ================ ========================================================
 440 Name   Section         Usage for ARMv8 Linux
 441 ===== ================ ========================================================
 442 _CCA   6.2.17          This method must be defined for all bus masters
 443                        on arm64 - there are no assumptions made about
 444                        whether such devices are cache coherent or not.
 445                        The _CCA value is inherited by all descendants of
 446                        these devices so it does not need to be repeated.
 447                        Without _CCA on arm64, the kernel does not know what
 448                        to do about setting up DMA for the device.
 449
 450                        NB: this method provides default cache coherency
 451                        attributes; the presence of an SMMU can be used to
 452                        modify that, however.  For example, a master could
 453                        default to non-coherent, but be made coherent with
 454                        the appropriate SMMU configuration (see Table 17 of
 455                        the IORT specification, ARM Document DEN 0049B).
 456
 457 _CID   6.1.2           Use as needed, see also _HID.
 458
 459 _CLS   6.1.3           Use as needed, see also _HID.
 460
 461 _CPC   8.4.7.1         Use as needed, power management specific.  CPPC is
 462                        recommended on arm64.
 463
 464 _CRS   6.2.2           Required on arm64.
 465
 466 _CSD   8.4.2.2         Use as needed, used only in conjunction with _CST.
 467
 468 _CST   8.4.2.1         Low power idle states (8.4.4) are recommended instead
 469                        of C-states.
 470
 471 _DDN   6.1.4           This field can be used for a device name.  However,
 472                        it is meant for DOS device names (e.g., COM1), so be
 473                        careful of its use across OSes.
 474
 475 _DSD   6.2.5           To be used with caution.  If this object is used, try
 476                        to use it within the constraints already defined by the
 477                        Device Properties UUID.  Only in rare circumstances
 478                        should it be necessary to create a new _DSD UUID.
 479
 480                        In either case, submit the _DSD definition along with
 481                        any driver patches for discussion, especially when
 482                        device properties are used.  A driver will not be
 483                        considered complete without a corresponding _DSD
 484                        description.  Once approved by kernel maintainers,
 485                        the UUID or device properties must then be registered
 486                        with the UEFI Forum; this may cause some iteration as
 487                        more than one OS will be registering entries.
 488
 489 _DSM   9.1.1           Do not use this method.  It is not standardized, the
 490                        return values are not well documented, and it is
 491                        currently a frequent source of error.
 492
 493 \_GL   5.7.1           This object is not to be used in hardware reduced
 494                        mode, and therefore should not be used on arm64.
 495
 496 _GLK   6.5.7           This object requires a global lock be defined; there
 497                        is no global lock on arm64 since it runs in hardware
 498                        reduced mode.  Hence, do not use this object on arm64.
 499
 500 \_GPE  5.3.1           This namespace is for x86 use only.  Do not use it
 501                        on arm64.
 502
 503 _HID   6.1.5           This is the primary object to use in device probing,
 504                        though _CID and _CLS may also be used.
 505
 506 _INI   6.5.1           Not required, but can be useful in setting up devices
 507                        when UEFI leaves them in a state that may not be what
 508                        the driver expects before it starts probing.
 509
 510 _LPI   8.4.4.3         Recommended for use with processor definitions (_HID
 511                        ACPI0010) on arm64.  See also _RDI.
 512
 513 _MLS   6.1.7           Highly recommended for use in internationalization.
 514
 515 _OFF   7.2.2           It is recommended to define this method for any device
 516                        that can be turned on or off.
 517
 518 _ON    7.2.3           It is recommended to define this method for any device
 519                        that can be turned on or off.
 520
 521 \_OS   5.7.3           This method will return "Linux" by default (this is
 522                        the value of the macro ACPI_OS_NAME on Linux).  The
 523                        command line parameter acpi_os=<string> can be used
 524                        to set it to some other value.
 525
 526 _OSC   6.2.11          This method can be a global method in ACPI (i.e.,
 527                        \_SB._OSC), or it may be associated with a specific
 528                        device (e.g., \_SB.DEV0._OSC), or both.  When used
 529                        as a global method, only capabilities published in
 530                        the ACPI specification are allowed.  When used as
 531                        a device-specific method, the process described for
 532                        using _DSD MUST be used to create an _OSC definition;
 533                        out-of-process use of _OSC is not allowed.  That is,
 534                        submit the device-specific _OSC usage description as
 535                        part of the kernel driver submission, get it approved
 536                        by the kernel community, then register it with the
 537                        UEFI Forum.
 538
 539 \_OSI  5.7.2           Deprecated on ARM64.  As far as ACPI firmware is
 540                        concerned, _OSI is not to be used to determine what
 541                        sort of system is being used or what functionality
 542                        is provided.  The _OSC method is to be used instead.
 543
 544 _PDC   8.4.1           Deprecated, do not use on arm64.
 545
 546 \_PIC  5.8.1           The method should not be used.  On arm64, the only
 547                        interrupt model available is GIC.
 548
 549 \_PR   5.3.1           This namespace is for x86 use only on legacy systems.
 550                        Do not use it on arm64.
 551
 552 _PRT   6.2.13          Required as part of the definition of all PCI root
 553                        devices.
 554
 555 _PRx   7.3.8-11        Use as needed; power management specific.  If _PR0 is
 556                        defined, _PR3 must also be defined.
 557
 558 _PSx   7.3.2-5         Use as needed; power management specific.  If _PS0 is
 559                        defined, _PS3 must also be defined.  If clocks or
 560                        regulators need adjusting to be consistent with power
 561                        usage, change them in these methods.
 562
 563 _RDI   8.4.4.4         Recommended for use with processor definitions (_HID
 564                        ACPI0010) on arm64.  This should only be used in
 565                        conjunction with _LPI.
 566
 567 \_REV  5.7.4           Always returns the latest version of ACPI supported.
 568
 569 \_SB   5.3.1           Required on arm64; all devices must be defined in this
 570                        namespace.
 571
 572 _SLI   6.2.15          Use is recommended when SLIT table is in use.
 573
 574 _STA   6.3.7,          It is recommended to define this method for any device
 575        7.2.4           that can be turned on or off.  See also the STAO table
 576                        that provides overrides to hide devices in virtualized
 577                        environments.
 578
 579 _SRS   6.2.16          Use as needed; see also _PRS.
 580
 581 _STR   6.1.10          Recommended for conveying device names to end users;
 582                        this is preferred over using _DDN.
 583
 584 _SUB   6.1.9           Use as needed; _HID or _CID are preferred.
 585
 586 _SUN   6.1.11          Use as needed, but recommended.
 587
 588 _SWS   7.4.3           Use as needed; power management specific; this may
 589                        require specification changes for use on arm64.
 590
 591 _UID   6.1.12          Recommended for distinguishing devices of the same
 592                        class; define it if at all possible.
 593 ===== ================ ========================================================
 594
 595
 596
 597
 598 ACPI Event Model
 599 ----------------
 600 Do not use GPE block devices; these are not supported in the hardware reduced
 601 profile used by arm64.  Since there are no GPE blocks defined for use on ARM
 602 platforms, ACPI events must be signaled differently.
 603
 604 There are two options: GPIO-signaled interrupts (Section 5.6.5), and
 605 interrupt-signaled events (Section 5.6.9).  Interrupt-signaled events are a
 606 new feature in the ACPI 6.1 specification.  Either - or both - can be used
 607 on a given platform, and which to use may be dependent of limitations in any
 608 given SoC.  If possible, interrupt-signaled events are recommended.
 609
 610
 611 ACPI Processor Control
 612 ----------------------
 613 Section 8 of the ACPI specification changed significantly in version 6.0.
 614 Processors should now be defined as Device objects with _HID ACPI0007; do
 615 not use the deprecated Processor statement in ASL.  All multiprocessor systems
 616 should also define a hierarchy of processors, done with Processor Container
 617 Devices (see Section 8.4.3.1, _HID ACPI0010); do not use processor aggregator
 618 devices (Section 8.5) to describe processor topology.  Section 8.4 of the
 619 specification describes the semantics of these object definitions and how
 620 they interrelate.
 621
 622 Most importantly, the processor hierarchy defined also defines the low power
 623 idle states that are available to the platform, along with the rules for
 624 determining which processors can be turned on or off and the circumstances
 625 that control that.  Without this information, the processors will run in
 626 whatever power state they were left in by UEFI.
 627
 628 Note too, that the processor Device objects defined and the entries in the
 629 MADT for GICs are expected to be in synchronization.  The _UID of the Device
 630 object must correspond to processor IDs used in the MADT.
 631
 632 It is recommended that CPPC (8.4.5) be used as the primary model for processor
 633 performance control on arm64.  C-states and P-states may become available at
 634 some point in the future, but most current design work appears to favor CPPC.
 635
 636 Further, it is essential that the ARMv8 SoC provide a fully functional
 637 implementation of PSCI; this will be the only mechanism supported by ACPI
 638 to control CPU power state.  Booting of secondary CPUs using the ACPI
 639 parking protocol is possible, but discouraged, since only PSCI is supported
 640 for ARM servers.
 641
 642
 643 ACPI System Address Map Interfaces
 644 ----------------------------------
 645 In Section 15 of the ACPI specification, several methods are mentioned as
 646 possible mechanisms for conveying memory resource information to the kernel.
 647 For arm64, we will only support UEFI for booting with ACPI, hence the UEFI
 648 GetMemoryMap() boot service is the only mechanism that will be used.
 649
 650
 651 ACPI Platform Error Interfaces (APEI)
 652 -------------------------------------
 653 The APEI tables supported are described above.
 654
 655 APEI requires the equivalent of an SCI and an NMI on ARMv8.  The SCI is used
 656 to notify the OSPM of errors that have occurred but can be corrected and the
 657 system can continue correct operation, even if possibly degraded.  The NMI is
 658 used to indicate fatal errors that cannot be corrected, and require immediate
 659 attention.
 660
 661 Since there is no direct equivalent of the x86 SCI or NMI, arm64 handles
 662 these slightly differently.  The SCI is handled as a high priority interrupt;
 663 given that these are corrected (or correctable) errors being reported, this
 664 is sufficient.  The NMI is emulated as the highest priority interrupt
 665 possible.  This implies some caution must be used since there could be
 666 interrupts at higher privilege levels or even interrupts at the same priority
 667 as the emulated NMI.  In Linux, this should not be the case but one should
 668 be aware it could happen.
 669
 670
 671 ACPI Objects Not Supported on ARM64
 672 -----------------------------------
 673 While this may change in the future, there are several classes of objects
 674 that can be defined, but are not currently of general interest to ARM servers.
 675 Some of these objects have x86 equivalents, and may actually make sense in ARM
 676 servers.  However, there is either no hardware available at present, or there
 677 may not even be a non-ARM implementation yet.  Hence, they are not currently
 678 supported.
 679
 680 The following classes of objects are not supported:
 681
 682        -  Section 9.2: ambient light sensor devices
 683
 684        -  Section 9.3: battery devices
 685
 686        -  Section 9.4: lids (e.g., laptop lids)
 687
 688        -  Section 9.8.2: IDE controllers
 689
 690        -  Section 9.9: floppy controllers
 691
 692        -  Section 9.10: GPE block devices
 693
 694        -  Section 9.15: PC/AT RTC/CMOS devices
 695
 696        -  Section 9.16: user presence detection devices
 697
 698        -  Section 9.17: I/O APIC devices; all GICs must be enumerable via MADT
 699
 700        -  Section 9.18: time and alarm devices (see 9.15)
 701
 702        -  Section 10: power source and power meter devices
 703
 704        -  Section 11: thermal management
 705
 706        -  Section 12: embedded controllers interface
 707
 708        -  Section 13: SMBus interfaces
 709
 710
 711 This also means that there is no support for the following objects:
 712
 713 ====   =========================== ====   ==========
 714 Name   Section                     Name   Section
 715 ====   =========================== ====   ==========
 716 _ALC   9.3.4                       _FDM   9.10.3
 717 _ALI   9.3.2                       _FIX   6.2.7
 718 _ALP   9.3.6                       _GAI   10.4.5
 719 _ALR   9.3.5                       _GHL   10.4.7
 720 _ALT   9.3.3                       _GTM   9.9.2.1.1
 721 _BCT   10.2.2.10                   _LID   9.5.1
 722 _BDN   6.5.3                       _PAI   10.4.4
 723 _BIF   10.2.2.1                    _PCL   10.3.2
 724 _BIX   10.2.2.1                    _PIF   10.3.3
 725 _BLT   9.2.3                       _PMC   10.4.1
 726 _BMA   10.2.2.4                    _PMD   10.4.8
 727 _BMC   10.2.2.12                   _PMM   10.4.3
 728 _BMD   10.2.2.11                   _PRL   10.3.4
 729 _BMS   10.2.2.5                    _PSR   10.3.1
 730 _BST   10.2.2.6                    _PTP   10.4.2
 731 _BTH   10.2.2.7                    _SBS   10.1.3
 732 _BTM   10.2.2.9                    _SHL   10.4.6
 733 _BTP   10.2.2.8                    _STM   9.9.2.1.1
 734 _DCK   6.5.2                       _UPD   9.16.1
 735 _EC    12.12                       _UPP   9.16.2
 736 _FDE   9.10.1                      _WPC   10.5.2
 737 _FDI   9.10.2                      _WPP   10.5.3
 738 ====   =========================== ====   ==========