ARM64: ACPI: Update documentation for latest specification version

       -- Required: DSDT, FADT, GTDT, MADT, MCFG, RSDP, SPCR, XSDT

       -- Recommended: BERT, EINJ, ERST, HEST, SSDT

       -- Recommended: BERT, EINJ, ERST, HEST, PCCT, 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

       -- Optional: BGRT, CPEP, CSRT, DBG2, DRTM, ECDT, FACS, FPDT, IORT,

          MCHI, MPST, MSCT, NFIT, PMTT, RASF, SBST, SLIT, SPMI, SRAT, STAO,

	  TCPA, TPM2, UEFI, XENV

       -- Not supported: BOOT, DBGP, DMAR, ETDT, HPET, IBFT, IVRS, LPIT,

          MSDM, OEMx, PSDT, RSDT, SLIC, WAET, WDAT, WDRT, WPBT

Table  Usage for ARMv8 Linux

-----  ----------------------------------------------------------------

DBG2   Signature Reserved (signature == "DBG2")

       == DeBuG port table 2 ==

       Microsoft only table, will not be supported.

       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 ==

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.

       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.

       == 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; future versions have been adapted for

       use with ARM and will be recommended in order to support ACPI power

       management.

       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 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 - 0xE).

       should be used (types 0xA - 0xF).

MCFG   Signature Reserved (signature == "MCFG")

       == Memory-mapped ConFiGuration space ==

       == 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.

MSCT   Section 5.2.19 (signature == "MSCT")

       == Maximum System Characteristic Table ==

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.

PMTT   Section 5.2.21.12 (signature == "PMTT")

       == Platform Memory Topology Table ==

       Optional, not currently supported.

PSDT   Section 5.2.11.3 (signature == "PSDT")

       == Persistent System Description Table ==

       Obsolete table, will not be supported.

RASF   Section 5.2.20 (signature == "RASF")

       == RAS Feature table ==

       Optional, not currently supported.

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.

       on arm64, and will not be used.  If provided, it will be ignored.

SBST   Section 5.2.14 (signature == "SBST")

       == Smart Battery Subsystem Table ==

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.

       To support arm64 NUMA, this table is required.

SSDT   Section 5.2.11.2 (signature == "SSDT")

       == Secondary System Description Table ==

       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

       == 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 are discussed in the list that

follows:

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

----   ------------    -------------------------------------------------

_ADR   6.1.1           Use as needed.

_BBN   6.5.5           Use as needed; PCI-specific.

_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.

_BDN   6.5.3           Optional; not likely to be used on arm64.

                       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).

_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.

_CID   6.1.2           Use as needed, see also _HID.

_CDM   6.2.1           Optional, to be used only for processor devices.

_CLS   6.1.3           Use as needed, see also _HID.

_CID   6.1.2           Use as needed.

_CLS   6.1.3           Use as needed.

_CPC   8.4.7.1         Use as needed, power management specific.  CPPC is

                       recommended on arm64.

_CRS   6.2.2           Required on arm64.

_DCK   6.5.2           Optional; not likely to be used 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.

_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

                       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

_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.

_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.

\_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.

_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.

_IRC   7.2.15          Use as needed; power management specific.

_LCK   6.3.4           Optional.

_LPI   8.4.4.3         Recommended for use with processor definitions (_HID

		       ACPI0010) on arm64.  See also _RDI.

_MAT   6.2.10          Optional; see also the MADT.

_MLS   6.1.7           Highly recommended for use in internationalization.

_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

_OFF   7.2.2           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

_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

                       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.

\_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.

_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

_PRx   7.3.8-11        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

_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.

\_PTS  7.3.1           Use as needed; power management specific.

_PXM   6.2.14          Optional.

_REG   6.5.4           Use as needed.

_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.

_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.

_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

       7.1.4           that can be turned on or off.

       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          Optional; see also _PRS.

_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          Optional.

\_Sx   7.3.2           Use as needed; power management specific.

_SUN   6.1.11          Use as needed, but recommended.

_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

_SWS   7.4.3           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.

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 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.

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 (including secondary CPU booting).

More details will be provided on the release of the ACPI 6.0 specification.

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

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.

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.

These are not supported:

The following classes of objects are not supported:

       -- Section 9.2: ambient light sensor devices

       -- 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 13: SMBus interfaces

       -- Section 17: NUMA support (prototypes have been submitted for

          review)

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