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Documentation/arm64: Update ARM and arch reference
This patch clarifies that both Armv8 and v9 are in scope, not just Armv8 systems. Also, ARM is re-written as Arm. Cc: Jeremy Linton <Jeremy.Linton@arm.com> Cc: James Morse <James.Morse@arm.com> Cc: Rob Herring <Rob.Herring@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Hanjun Guo <guohanjun@huawei.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-doc@vger.kernel.org Cc: linux-acpi@vger.kernel.org Signed-off-by: Jose Marinho <jose.marinho@arm.com> Reviewed-by: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Acked-by: Sudeep Holla <sudeep.holla@arm.com> Reviewed-by: Jeremy Linton <jeremy.linton@arm.com> Reviewed-by: Hanjun Guo <guohanjun@huawei.com> Link: https://lore.kernel.org/r/20230606093528.1494344-2-jose.marinho@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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Jose Marinho
Catalin Marinas
parent
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commit
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@ -1,40 +1,41 @@
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=====================
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ACPI on ARMv8 Servers
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=====================
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===================
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ACPI on Arm systems
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===================
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ACPI can be used for ARMv8 general purpose servers designed to follow
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the ARM SBSA (Server Base System Architecture) [0] and SBBR (Server
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ACPI can be used for Armv8 and Armv9 systems designed to follow
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the Arm SBSA (Server Base System Architecture) [0] and SBBR (Server
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Base Boot Requirements) [1] specifications. Please note that the SBBR
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can be retrieved simply by visiting [1], but the SBSA is currently only
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available to those with an ARM login due to ARM IP licensing concerns.
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The ARMv8 kernel implements the reduced hardware model of ACPI version
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The Arm kernel implements the reduced hardware model of ACPI version
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5.1 or later. Links to the specification and all external documents
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it refers to are managed by the UEFI Forum. The specification is
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available at http://www.uefi.org/specifications and documents referenced
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by the specification can be found via http://www.uefi.org/acpi.
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If an ARMv8 system does not meet the requirements of the SBSA and SBBR,
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If an Arm system does not meet the requirements of the BSA and BBR,
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or cannot be described using the mechanisms defined in the required ACPI
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specifications, then ACPI may not be a good fit for the hardware.
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While the documents mentioned above set out the requirements for building
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industry-standard ARMv8 servers, they also apply to more than one operating
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industry-standard Arm systems, they also apply to more than one operating
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system. The purpose of this document is to describe the interaction between
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ACPI and Linux only, on an ARMv8 system -- that is, what Linux expects of
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ACPI and Linux only, on an Arm system -- that is, what Linux expects of
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ACPI and what ACPI can expect of Linux.
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Why ACPI on ARM?
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Why ACPI on Arm?
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----------------
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Before examining the details of the interface between ACPI and Linux, it is
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useful to understand why ACPI is being used. Several technologies already
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exist in Linux for describing non-enumerable hardware, after all. In this
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section we summarize a blog post [2] from Grant Likely that outlines the
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reasoning behind ACPI on ARMv8 servers. Actually, we snitch a good portion
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reasoning behind ACPI on Arm systems. Actually, we snitch a good portion
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of the summary text almost directly, to be honest.
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The short form of the rationale for ACPI on ARM is:
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The short form of the rationale for ACPI on Arm is:
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- ACPI’s byte code (AML) allows the platform to encode hardware behavior,
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while DT explicitly does not support this. For hardware vendors, being
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@ -47,7 +48,7 @@ The short form of the rationale for ACPI on ARM is:
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- In the enterprise server environment, ACPI has established bindings (such
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as for RAS) which are currently used in production systems. DT does not.
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Such bindings could be defined in DT at some point, but doing so means ARM
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Such bindings could be defined in DT at some point, but doing so means Arm
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and x86 would end up using completely different code paths in both firmware
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and the kernel.
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@ -108,7 +109,7 @@ recent version of the kernel.
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Relationship with Device Tree
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-----------------------------
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ACPI support in drivers and subsystems for ARMv8 should never be mutually
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ACPI support in drivers and subsystems for Arm should never be mutually
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exclusive with DT support at compile time.
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At boot time the kernel will only use one description method depending on
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@ -121,11 +122,11 @@ time).
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Booting using ACPI tables
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-------------------------
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The only defined method for passing ACPI tables to the kernel on ARMv8
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The only defined method for passing ACPI tables to the kernel on Arm
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is via the UEFI system configuration table. Just so it is explicit, this
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means that ACPI is only supported on platforms that boot via UEFI.
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When an ARMv8 system boots, it can either have DT information, ACPI tables,
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When an Arm system boots, it can either have DT information, ACPI tables,
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or in some very unusual cases, both. If no command line parameters are used,
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the kernel will try to use DT for device enumeration; if there is no DT
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present, the kernel will try to use ACPI tables, but only if they are present.
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@ -448,7 +449,7 @@ ASWG
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----
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The ACPI specification changes regularly. During the year 2014, for instance,
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version 5.1 was released and version 6.0 substantially completed, with most of
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the changes being driven by ARM-specific requirements. Proposed changes are
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the changes being driven by Arm-specific requirements. Proposed changes are
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presented and discussed in the ASWG (ACPI Specification Working Group) which
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is a part of the UEFI Forum. The current version of the ACPI specification
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is 6.1 release in January 2016.
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@ -456,7 +457,7 @@ is 6.1 release in January 2016.
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Participation in this group is open to all UEFI members. Please see
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http://www.uefi.org/workinggroup for details on group membership.
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It is the intent of the ARMv8 ACPI kernel code to follow the ACPI specification
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It is the intent of the Arm ACPI kernel code to follow the ACPI specification
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as closely as possible, and to only implement functionality that complies with
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the released standards from UEFI ASWG. As a practical matter, there will be
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vendors that provide bad ACPI tables or violate the standards in some way.
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@ -470,12 +471,12 @@ likely be willing to assist in submitting ECRs.
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Linux Code
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----------
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Individual items specific to Linux on ARM, contained in the Linux
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Individual items specific to Linux on Arm, contained in the Linux
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source code, are in the list that follows:
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ACPI_OS_NAME
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This macro defines the string to be returned when
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an ACPI method invokes the _OS method. On ARM64
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an ACPI method invokes the _OS method. On Arm
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systems, this macro will be "Linux" by default.
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The command line parameter acpi_os=<string>
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can be used to set it to some other value. The
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