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ARM64: ACPI: Update documentation for latest specification version 

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.

Signed-off-by: Al Stone <al.stone@linaro.org>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Reviewed-by: Roy Franz <roy.franz@hpe.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
steinar/wifi_calib_4_9_kernel
Al Stone 2016-06-13 15:41:55 -06:00 committed by Catalin Marinas
parent 5e4c7549f7
commit 83ce0efc12
2 changed files with 212 additions and 169 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

341
Documentation/arm64/acpi_object_usage.txt
View File

@ -13,14 +13,14 @@ 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
-- 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
----- ----------------------------------------------------------------
@ -50,7 +50,8 @@ 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 +134,11 @@ 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 +151,30 @@ 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
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 ==
@ -176,14 +188,38 @@ 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; 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.
@ -195,7 +231,7 @@ 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 ==
@ -220,7 +256,7 @@ 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 5.2.11.2 (signature == "SSDT")
== Secondary System Description Table ==
@ -235,6 +271,11 @@ SSDT Section 5.2.11.2 (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 +307,10 @@ 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 +318,46 @@ XSDT Section 5.2.8 (signature == "XSDT")
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.
_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 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
@ -325,20 +372,10 @@ _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 +386,22 @@ _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
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.
_LPI 8.4.4.3 Recommended for use with processor definitions (_HID
ACPI0010) on arm64. See also _RDI.
_LCK 6.3.4 Optional.
_MLS 6.1.7 Highly recommended for use in internationalization.
_MAT 6.2.10 Optional; see also the MADT.
_MLS 6.1.7 Optional, but highly recommended for use in
internationalization.
_OFF 7.1.2 It is recommended to define this method for any device
_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 +422,107 @@ _OSC 6.2.11 This method can be a global method in ACPI (i.e.,
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.
_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.
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.
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.
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
@ -535,21 +544,25 @@ used to indicate fatal errors that cannot be corrected, and require immediate
attention.
Since there is no direct equivalent of the x86 SCI or NMI, arm64 handles
these slightly differently. The SCI is handled as a normal GPIO-signaled
interrupt; given that these are corrected (or correctable) errors being
reported, this is sufficient. The NMI is emulated as the highest priority
GPIO-signaled interrupt possible. This implies some caution must be used
since there could be interrupts at higher privilege levels or even interrupts
at the same priority as the emulated NMI. In Linux, this should not be the
case but one should be aware it could happen.
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
@ -571,16 +584,6 @@ 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 +592,31 @@ Not yet implemented are:
-- 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

40
Documentation/arm64/arm-acpi.txt
View File

@ -34,7 +34,7 @@ of the summary text almost directly, to be honest.
The short form of the rationale for ACPI on ARM is:
-- ACPI’s bytecode (AML) allows the platform to encode hardware behavior,
-- ACPI’s byte code (AML) allows the platform to encode hardware behavior,
while DT explicitly does not support this. For hardware vendors, being
able to encode behavior is a key tool used in supporting operating
system releases on new hardware.
@ -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
@ -110,7 +110,7 @@ ACPI support in drivers and subsystems for ARMv8 should never be mutually
exclusive with DT support at compile time.
At boot time the kernel will only use one description method depending on
parameters passed from the bootloader (including kernel bootargs).
parameters passed from the boot loader (including kernel bootargs).
Regardless of whether DT or ACPI is used, the kernel must always be capable
of booting with either scheme (in kernels with both schemes enabled at compile
@ -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 specification):
-- RSDP (Root System Description Pointer), section 5.2.5
@ -185,9 +185,23 @@ 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 necessary to describe the I/O topology, SMMUs and GIC ITSs,
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.
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.
ACPI Detection
@ -198,7 +212,7 @@ the device structure. This is detailed further in the "Driver
Recommendations" section.
In non-driver code, if the presence of ACPI needs to be detected at
runtime, then check the value of acpi_disabled. If CONFIG_ACPI is not
run time, then check the value of acpi_disabled. If CONFIG_ACPI is not
set, acpi_disabled will always be 1.
@ -233,7 +247,7 @@ 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 +448,8 @@ 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.
@ -443,7 +458,7 @@ It is the intent of the ARMv8 ACPI kernel code to follow the ACPI specification
as closely as possible, and to only implement functionality that complies with
the released standards from UEFI ASWG. As a practical matter, there will be
vendors that provide bad ACPI tables or violate the standards in some way.
If this is because of errors, quirks and fixups may be necessary, but will
If this is because of errors, quirks and fix-ups may be necessary, but will
be avoided if possible. If there are features missing from ACPI that preclude
it from being used on a platform, ECRs (Engineering Change Requests) should be
submitted to ASWG and go through the normal approval process; for those that
@ -480,8 +495,7 @@ References
Software on ARM Platforms", dated 16 Aug 2014
[2] http://www.secretlab.ca/archives/151, 10 Jan 2015, Copyright (c) 2015,
Linaro Ltd., written by Grant Likely. A copy of the verbatim text (apart
from formatting) is also in Documentation/arm64/why_use_acpi.txt.
Linaro Ltd., written by Grant Likely.
[3] AMD ACPI for Seattle platform documentation:
http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/Seattle_ACPI_Guide.pdf