[PATCH v4] ARM64: ACPI: Update documentation for latest specification version
From: Al Stone
Date: Mon Apr 18 2016 - 15:32:40 EST
The ACPI 6.1 specification was recently released at the end of January
2016, but the arm64 kernel documentation for the use of ACPI was written
for the 5.1 version of the spec. There were significant additions to the
spec that had not yet been mentioned -- for example, the 6.0 mechanisms
added to make it easier to define processors and low power idle states,
as well as the 6.1 addition allowing regular interrupts (not just from
GPIO) be used to signal ACPI general purpose events.
This patch reflects going back through and examining the specs in detail
and updating content appropriately. Whilst there, a few odds and ends of
typos were caught as well. This brings the documentation up to date with
ACPI 6.1 for arm64.
Changes for v4:
-- Clarify that IORT can sometimes be optional (Jon Masters).
-- Remove "Use as needed" descriptions of ACPI objects; they provide
no substantive information and doing so simplifies maintenance of
this document over time. These have been replaced with a simpler
notice that states that unless otherwise noted, do what the APCI
specification says is needed.
-- Corrected the _OSI object usage recommendation; it described kernel
behavior that does not exist (Al Stone).
Changes for v3:
-- Clarify use of _LPI/_RDI (Vikas Sajjan)
-- Whitespace cleanup as pointed out by checkpatch
Changes for v2:
-- Clean up white space (Harb Abdulhahmid)
-- Clarification on _CCA usage (Harb Abdulhamid)
-- IORT moved to required from recommended (Hanjun Guo)
-- Clarify IORT description (Hanjun Guo)
Signed-off-by: Al Stone <al.stone@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Documentation/arm64/acpi_object_usage.txt | 347 ++++++++++++++++--------------
Documentation/arm64/arm-acpi.txt | 28 ++-
2 files changed, 212 insertions(+), 163 deletions(-)
diff --git a/Documentation/arm64/acpi_object_usage.txt b/Documentation/arm64/acpi_object_usage.txt
index a6e1a18..3891750 100644
@@ -13,14 +13,18 @@ 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
+ -- 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
+ -- Optional: BGRT, CPEP, CSRT, DBG2, DRTM, ECDT, FACS, FPDT, MCHI,
+ MPST, MSCT, NFIT, PMTT, RASF, SBST, SLIT, SPMI, SRAT, STAO, TCPA,
+ TPM2, UEFI, XENV
- -- Not supported: BOOT, DBG2, DBGP, DMAR, ETDT, HPET, IBFT, IVRS,
- LPIT, MSDM, RSDT, SLIC, WAET, WDAT, WDRT, WPBT
+ -- Not supported: BOOT, DBGP, DMAR, ETDT, HPET, IBFT, IVRS, LPIT,
+ MSDM, OEMx, PSDT, RSDT, SLIC, WAET, WDAT, WDRT, WPBT
+ -- NB: the IORT is required on certain SBSA platforms (e.g., when
+ using GICv3-ITS and an SMMU); it is optional on SBSA Level 0
Table Usage for ARMv8 Linux
@@ -50,7 +54,8 @@ CSRT Signature Reserved (signature == "CSRT")
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 ==
@@ -133,10 +138,11 @@ GTDT Section 5.2.24 (signature == "GTDT")
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.
@@ -149,20 +155,30 @@ 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; future versions have been adapted for
- use with ARM and will be recommended in order to support ACPI power
+ 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 ==
@@ -176,14 +192,38 @@ 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.
-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, and required when using CPPC to control
+ power on the platform.
+PMTT Section 184.108.40.206 (signature == "PMTT")
+ == Platform Memory Topology Table ==
+ Optional, but useful, but not currently supported.
+PSDT Section 220.127.116.11 (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.
@@ -195,7 +235,7 @@ RSDP Section 5.2.5 (signature == "RSD PTR")
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 ==
@@ -207,7 +247,7 @@ SLIC Signature Reserved (signature == "SLIC")
SLIT Section 5.2.17 (signature == "SLIT")
== System Locality distance Information Table ==
- Optional in general, but required for NUMA systems.
+ Optional in general, but required for arm64 NUMA systems.
SPCR Signature Reserved (signature == "SPCR")
== Serial Port Console Redirection table ==
@@ -220,7 +260,7 @@ SPMI Signature Reserved (signature == "SPMI")
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 18.104.22.168 (signature == "SSDT")
== Secondary System Description Table ==
@@ -235,6 +275,11 @@ SSDT Section 22.214.171.124 (signature == "SSDT")
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
@@ -266,6 +311,10 @@ 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.
@@ -273,44 +322,46 @@ XSDT Section 5.2.8 (signature == "XSDT")
-The expectations on individual ACPI objects are discussed in the list that
+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.
+_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.
-_BBN 6.5.5 Use as needed; PCI-specific.
+ 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).
-_BDN 6.5.3 Optional; not likely to be used on arm64.
+_CID 6.1.2 Use as needed, see also _HID.
-_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.
+_CLS 6.1.3 Use as needed, see also _HID.
-_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.
+_CPC 126.96.36.199 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 188.8.131.52 Use as needed, used only in conjunction with _CST.
+_CST 184.108.40.206 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
@@ -325,20 +376,10 @@ _DSD 6.2.5 To be used with caution. If this object is used, try
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.
@@ -349,35 +390,25 @@ _GLK 6.5.7 This object requires a global lock be defined; there
\_GPE 5.3.1 This namespace is for x86 use only. Do not use it
-_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.
+_HID 6.1.5 This is the primary object to use in device probing,
+ though _CID and _CLS may also be used.
-_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.
+_HRV 6.1.6 Use 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.
+_LPI 220.127.116.11 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
-_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
@@ -398,122 +429,106 @@ _OSC 6.2.11 This method can be a global method in ACPI (i.e.,
by the kernel community, then register it with the
-\_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
-_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 18.104.22.168 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
-_SEG 6.5.6 Use as needed; PCI-specific.
-\_SI 5.3.1, Optional.
-_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
-_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.
+_SUN 6.1.11 Use as needed, but recommended.
-\_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
+_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 22.214.171.124, _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
+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 sychronization. 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 may be possible using
+parking protocol, but only PSCI is to be used for ARM servers.
ACPI System Address Map Interfaces
@@ -535,21 +550,25 @@ used to indicate fatal errors that cannot be corrected, and require immediate
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
-These are not supported:
+The following classes of objects are not supported:
-- Section 9.2: ambient light sensor devices
@@ -571,16 +590,6 @@ These are not supported:
-- 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
@@ -589,5 +598,31 @@ Not yet implemented are:
-- Section 13: SMBus interfaces
- -- Section 17: NUMA support (prototypes have been submitted for
+This also mean 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 126.96.36.199.1
+_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 188.8.131.52.1
+_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
diff --git a/Documentation/arm64/arm-acpi.txt b/Documentation/arm64/arm-acpi.txt
index 570a4f8..12381c1 100644
@@ -57,11 +57,11 @@ The short form of the rationale for ACPI on ARM is:
-- The new ACPI governance process works well and Linux is now at the same
table as hardware vendors and other OS vendors. In fact, there is no
- longer any reason to feel that ACPI is only belongs to Windows or that
+ longer any reason to feel that ACPI only belongs to Windows or that
Linux is in any way secondary to Microsoft in this arena. The move of
ACPI governance into the UEFI forum has significantly opened up the
specification development process, and currently, a large portion of the
- changes being made to ACPI is being driven by Linux.
+ changes being made to ACPI are being driven by Linux.
Key to the use of ACPI is the support model. For servers in general, the
responsibility for hardware behaviour cannot solely be the domain of the
@@ -159,7 +159,7 @@ Further, the ACPI core will only use the 64-bit address fields in the FADT
(Fixed ACPI Description Table). Any 32-bit address fields in the FADT will
be ignored on arm64.
-Hardware reduced mode (see Section 4.1 of the ACPI 5.1 specification) will
+Hardware reduced mode (see Section 4.1 of the ACPI 6.1 specification) will
be enforced by the ACPI core on arm64. Doing so allows the ACPI core to
run less complex code since it no longer has to provide support for legacy
hardware from other architectures. Any fields that are not to be used for
@@ -167,7 +167,7 @@ hardware reduced mode must be set to zero.
For the ACPI core to operate properly, and in turn provide the information
the kernel needs to configure devices, it expects to find the following
-tables (all section numbers refer to the ACPI 5.1 specfication):
+tables (all section numbers refer to the ACPI 6.1 specfication):
-- RSDP (Root System Description Pointer), section 5.2.5
@@ -185,9 +185,22 @@ tables (all section numbers refer to the ACPI 5.1 specfication):
-- If PCI is supported, the MCFG (Memory mapped ConFiGuration
Table), section 5.2.6, specifically Table 5-31.
+ -- If booting without a console=<device> kernel parameter is
+ supported, the SPCR (Serial Port Console Redirection table),
+ section 5.2.6, specifically Table 5-31.
+ -- If virtualization is supported, the IORT (Input Output Remapping
+ Table, section 5.2.6, specifically Table 5-31.
+ -- If NUMA is supported, the SRAT (System Resource Affinity Table)
+ and SLIT (System Locality distance Information Table), sections
+ 5.2.16 and 5.2.17, respectively.
If the above tables are not all present, the kernel may or may not be
able to boot properly since it may not be able to configure all of the
+devices available. This list of tables is not meant to be all inclusive;
+in some environments other tables may be needed (e.g., any of the APEI
+tables from section 18) to support specific functionality.
@@ -233,7 +246,7 @@ that looks like this: Name(KEY0, "value0"). An ACPI device driver would
then retrieve the value of the property by evaluating the KEY0 object.
However, using Name() this way has multiple problems: (1) ACPI limits
names ("KEY0") to four characters unlike DT; (2) there is no industry
-wide registry that maintains a list of names, minimzing re-use; (3)
+wide registry that maintains a list of names, minimizing re-use; (3)
there is also no registry for the definition of property values ("value0"),
again making re-use difficult; and (4) how does one maintain backward
compatibility as new hardware comes out? The _DSD method was created
@@ -434,7 +447,8 @@ The ACPI specification changes regularly. During the year 2014, for instance,
version 5.1 was released and version 6.0 substantially completed, with most of
the changes being driven by ARM-specific requirements. Proposed changes are
presented and discussed in the ASWG (ACPI Specification Working Group) which
-is a part of the UEFI Forum.
+is a part of the UEFI Forum. The current version of the ACPI specification
+is 6.1 release in January 2016.
Participation in this group is open to all UEFI members. Please see
http://www.uefi.org/workinggroup for details on group membership.