This patch clarifies that both Armv8 and v9 are in scope, not just Armv8 systems. Also, ARM is re-written as Arm. Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Jeremy Linton <Jeremy.Linton@xxxxxxx> Cc: James Morse <James.Morse@xxxxxxx> Cc: Rob Herring <Rob.Herring@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Cc: linux-doc@xxxxxxxxxxxxxxx Cc: linux-acpi@xxxxxxxxxxxxxxx Signed-off-by: Jose Marinho <jose.marinho@xxxxxxx> Reviewed-by: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@xxxxxxx> --- Documentation/arm64/arm-acpi.rst | 41 ++++++++++++++++---------------- 1 file changed, 21 insertions(+), 20 deletions(-) diff --git a/Documentation/arm64/arm-acpi.rst b/Documentation/arm64/arm-acpi.rst index 47ecb9930dde..1cafe38fc7f9 100644 --- a/Documentation/arm64/arm-acpi.rst +++ b/Documentation/arm64/arm-acpi.rst @@ -1,40 +1,41 @@ -===================== -ACPI on ARMv8 Servers -===================== +=================== +ACPI on Arm systems +=================== -ACPI can be used for ARMv8 general purpose servers designed to follow -the ARM SBSA (Server Base System Architecture) [0] and SBBR (Server +ACPI can be used for Armv8 and Armv9 systems designed to follow +the Arm SBSA (Server Base System Architecture) [0] and SBBR (Server Base Boot Requirements) [1] specifications. Please note that the SBBR can be retrieved simply by visiting [1], but the SBSA is currently only available to those with an ARM login due to ARM IP licensing concerns. -The ARMv8 kernel implements the reduced hardware model of ACPI version + +The Arm kernel implements the reduced hardware model of ACPI version 5.1 or later. Links to the specification and all external documents it refers to are managed by the UEFI Forum. The specification is available at http://www.uefi.org/specifications and documents referenced by the specification can be found via http://www.uefi.org/acpi. -If an ARMv8 system does not meet the requirements of the SBSA and SBBR, +If an Arm system does not meet the requirements of the BSA and BBR, or cannot be described using the mechanisms defined in the required ACPI specifications, then ACPI may not be a good fit for the hardware. While the documents mentioned above set out the requirements for building -industry-standard ARMv8 servers, they also apply to more than one operating +industry-standard Arm systems, they also apply to more than one operating system. The purpose of this document is to describe the interaction between -ACPI and Linux only, on an ARMv8 system -- that is, what Linux expects of +ACPI and Linux only, on an Arm system -- that is, what Linux expects of ACPI and what ACPI can expect of Linux. -Why ACPI on ARM? +Why ACPI on Arm? ---------------- Before examining the details of the interface between ACPI and Linux, it is useful to understand why ACPI is being used. Several technologies already exist in Linux for describing non-enumerable hardware, after all. In this section we summarize a blog post [2] from Grant Likely that outlines the -reasoning behind ACPI on ARMv8 servers. Actually, we snitch a good portion +reasoning behind ACPI on Arm systems. Actually, we snitch a good portion of the summary text almost directly, to be honest. -The short form of the rationale for ACPI on ARM is: +The short form of the rationale for ACPI on Arm is: - ACPI’s byte code (AML) allows the platform to encode hardware behavior, while DT explicitly does not support this. For hardware vendors, being @@ -47,7 +48,7 @@ The short form of the rationale for ACPI on ARM is: - In the enterprise server environment, ACPI has established bindings (such as for RAS) which are currently used in production systems. DT does not. - Such bindings could be defined in DT at some point, but doing so means ARM + Such bindings could be defined in DT at some point, but doing so means Arm and x86 would end up using completely different code paths in both firmware and the kernel. @@ -108,7 +109,7 @@ recent version of the kernel. Relationship with Device Tree ----------------------------- -ACPI support in drivers and subsystems for ARMv8 should never be mutually +ACPI support in drivers and subsystems for Arm should never be mutually exclusive with DT support at compile time. At boot time the kernel will only use one description method depending on @@ -121,11 +122,11 @@ time). Booting using ACPI tables ------------------------- -The only defined method for passing ACPI tables to the kernel on ARMv8 +The only defined method for passing ACPI tables to the kernel on Arm is via the UEFI system configuration table. Just so it is explicit, this means that ACPI is only supported on platforms that boot via UEFI. -When an ARMv8 system boots, it can either have DT information, ACPI tables, +When an Arm system boots, it can either have DT information, ACPI tables, or in some very unusual cases, both. If no command line parameters are used, the kernel will try to use DT for device enumeration; if there is no DT present, the kernel will try to use ACPI tables, but only if they are present. @@ -448,7 +449,7 @@ ASWG ---- 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 +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. The current version of the ACPI specification is 6.1 release in January 2016. @@ -456,7 +457,7 @@ 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. -It is the intent of the ARMv8 ACPI kernel code to follow the ACPI specification +It is the intent of the Arm 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. @@ -470,12 +471,12 @@ likely be willing to assist in submitting ECRs. Linux Code ---------- -Individual items specific to Linux on ARM, contained in the Linux +Individual items specific to Linux on Arm, contained in the Linux source code, are in the list that follows: ACPI_OS_NAME This macro defines the string to be returned when - an ACPI method invokes the _OS method. On ARM64 + an ACPI method invokes the _OS method. On Arm64 systems, this macro will be "Linux" by default. The command line parameter acpi_os=<string> can be used to set it to some other value. The -- 2.40.0.141.g8d90352acc
