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authorRob Herring <robh@kernel.org>2019-11-20 17:41:13 -0600
committerRob Herring <robh@kernel.org>2020-01-06 17:37:12 -0600
commitbaac82fe06db16f36bf216dd0c8ca0eaa1e28b97 (patch)
tree5a64ded6f996136180557d58194551886e924172 /Documentation/devicetree/bindings/arm/idle-states.yaml
parentdt-bindings: Rename Exynos to lowercase (diff)
downloadlinux-dev-baac82fe06db16f36bf216dd0c8ca0eaa1e28b97.tar.xz
linux-dev-baac82fe06db16f36bf216dd0c8ca0eaa1e28b97.zip
dt-bindings: arm: Convert arm,idle-state binding to DT schema
Convert the Arm idle-state binding to a DT schema. Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> Signed-off-by: Rob Herring <robh@kernel.org>
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+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/idle-states.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ARM idle states binding description
+
+maintainers:
+ - Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
+
+description: |+
+ ==========================================
+ 1 - Introduction
+ ==========================================
+
+ ARM systems contain HW capable of managing power consumption dynamically,
+ where cores can be put in different low-power states (ranging from simple wfi
+ to power gating) according to OS PM policies. The CPU states representing the
+ range of dynamic idle states that a processor can enter at run-time, can be
+ specified through device tree bindings representing the parameters required to
+ enter/exit specific idle states on a given processor.
+
+ According to the Server Base System Architecture document (SBSA, [3]), the
+ power states an ARM CPU can be put into are identified by the following list:
+
+ - Running
+ - Idle_standby
+ - Idle_retention
+ - Sleep
+ - Off
+
+ The power states described in the SBSA document define the basic CPU states on
+ top of which ARM platforms implement power management schemes that allow an OS
+ PM implementation to put the processor in different idle states (which include
+ states listed above; "off" state is not an idle state since it does not have
+ wake-up capabilities, hence it is not considered in this document).
+
+ Idle state parameters (e.g. entry latency) are platform specific and need to
+ be characterized with bindings that provide the required information to OS PM
+ code so that it can build the required tables and use them at runtime.
+
+ The device tree binding definition for ARM idle states is the subject of this
+ document.
+
+ ===========================================
+ 2 - idle-states definitions
+ ===========================================
+
+ Idle states are characterized for a specific system through a set of
+ timing and energy related properties, that underline the HW behaviour
+ triggered upon idle states entry and exit.
+
+ The following diagram depicts the CPU execution phases and related timing
+ properties required to enter and exit an idle state:
+
+ ..__[EXEC]__|__[PREP]__|__[ENTRY]__|__[IDLE]__|__[EXIT]__|__[EXEC]__..
+ | | | | |
+
+ |<------ entry ------->|
+ | latency |
+ |<- exit ->|
+ | latency |
+ |<-------- min-residency -------->|
+ |<------- wakeup-latency ------->|
+
+ Diagram 1: CPU idle state execution phases
+
+ EXEC: Normal CPU execution.
+
+ PREP: Preparation phase before committing the hardware to idle mode
+ like cache flushing. This is abortable on pending wake-up
+ event conditions. The abort latency is assumed to be negligible
+ (i.e. less than the ENTRY + EXIT duration). If aborted, CPU
+ goes back to EXEC. This phase is optional. If not abortable,
+ this should be included in the ENTRY phase instead.
+
+ ENTRY: The hardware is committed to idle mode. This period must run
+ to completion up to IDLE before anything else can happen.
+
+ IDLE: This is the actual energy-saving idle period. This may last
+ between 0 and infinite time, until a wake-up event occurs.
+
+ EXIT: Period during which the CPU is brought back to operational
+ mode (EXEC).
+
+ entry-latency: Worst case latency required to enter the idle state. The
+ exit-latency may be guaranteed only after entry-latency has passed.
+
+ min-residency: Minimum period, including preparation and entry, for a given
+ idle state to be worthwhile energywise.
+
+ wakeup-latency: Maximum delay between the signaling of a wake-up event and the
+ CPU being able to execute normal code again. If not specified, this is assumed
+ to be entry-latency + exit-latency.
+
+ These timing parameters can be used by an OS in different circumstances.
+
+ An idle CPU requires the expected min-residency time to select the most
+ appropriate idle state based on the expected expiry time of the next IRQ
+ (i.e. wake-up) that causes the CPU to return to the EXEC phase.
+
+ An operating system scheduler may need to compute the shortest wake-up delay
+ for CPUs in the system by detecting how long will it take to get a CPU out
+ of an idle state, e.g.:
+
+ wakeup-delay = exit-latency + max(entry-latency - (now - entry-timestamp), 0)
+
+ In other words, the scheduler can make its scheduling decision by selecting
+ (e.g. waking-up) the CPU with the shortest wake-up delay.
+ The wake-up delay must take into account the entry latency if that period
+ has not expired. The abortable nature of the PREP period can be ignored
+ if it cannot be relied upon (e.g. the PREP deadline may occur much sooner than
+ the worst case since it depends on the CPU operating conditions, i.e. caches
+ state).
+
+ An OS has to reliably probe the wakeup-latency since some devices can enforce
+ latency constraint guarantees to work properly, so the OS has to detect the
+ worst case wake-up latency it can incur if a CPU is allowed to enter an
+ idle state, and possibly to prevent that to guarantee reliable device
+ functioning.
+
+ The min-residency time parameter deserves further explanation since it is
+ expressed in time units but must factor in energy consumption coefficients.
+
+ The energy consumption of a cpu when it enters a power state can be roughly
+ characterised by the following graph:
+
+ |
+ |
+ |
+ e |
+ n | /---
+ e | /------
+ r | /------
+ g | /-----
+ y | /------
+ | ----
+ | /|
+ | / |
+ | / |
+ | / |
+ | / |
+ | / |
+ |/ |
+ -----|-------+----------------------------------
+ 0| 1 time(ms)
+
+ Graph 1: Energy vs time example
+
+ The graph is split in two parts delimited by time 1ms on the X-axis.
+ The graph curve with X-axis values = { x | 0 < x < 1ms } has a steep slope
+ and denotes the energy costs incurred while entering and leaving the idle
+ state.
+ The graph curve in the area delimited by X-axis values = {x | x > 1ms } has
+ shallower slope and essentially represents the energy consumption of the idle
+ state.
+
+ min-residency is defined for a given idle state as the minimum expected
+ residency time for a state (inclusive of preparation and entry) after
+ which choosing that state become the most energy efficient option. A good
+ way to visualise this, is by taking the same graph above and comparing some
+ states energy consumptions plots.
+
+ For sake of simplicity, let's consider a system with two idle states IDLE1,
+ and IDLE2:
+
+ |
+ |
+ |
+ | /-- IDLE1
+ e | /---
+ n | /----
+ e | /---
+ r | /-----/--------- IDLE2
+ g | /-------/---------
+ y | ------------ /---|
+ | / /---- |
+ | / /--- |
+ | / /---- |
+ | / /--- |
+ | --- |
+ | / |
+ | / |
+ |/ | time
+ ---/----------------------------+------------------------
+ |IDLE1-energy < IDLE2-energy | IDLE2-energy < IDLE1-energy
+ |
+ IDLE2-min-residency
+
+ Graph 2: idle states min-residency example
+
+ In graph 2 above, that takes into account idle states entry/exit energy
+ costs, it is clear that if the idle state residency time (i.e. time till next
+ wake-up IRQ) is less than IDLE2-min-residency, IDLE1 is the better idle state
+ choice energywise.
+
+ This is mainly down to the fact that IDLE1 entry/exit energy costs are lower
+ than IDLE2.
+
+ However, the lower power consumption (i.e. shallower energy curve slope) of
+ idle state IDLE2 implies that after a suitable time, IDLE2 becomes more energy
+ efficient.
+
+ The time at which IDLE2 becomes more energy efficient than IDLE1 (and other
+ shallower states in a system with multiple idle states) is defined
+ IDLE2-min-residency and corresponds to the time when energy consumption of
+ IDLE1 and IDLE2 states breaks even.
+
+ The definitions provided in this section underpin the idle states
+ properties specification that is the subject of the following sections.
+
+ ===========================================
+ 3 - idle-states node
+ ===========================================
+
+ ARM processor idle states are defined within the idle-states node, which is
+ a direct child of the cpus node [1] and provides a container where the
+ processor idle states, defined as device tree nodes, are listed.
+
+ On ARM systems, it is a container of processor idle states nodes. If the
+ system does not provide CPU power management capabilities, or the processor
+ just supports idle_standby, an idle-states node is not required.
+
+ ===========================================
+ 4 - References
+ ===========================================
+
+ [1] ARM Linux Kernel documentation - CPUs bindings
+ Documentation/devicetree/bindings/arm/cpus.yaml
+
+ [2] ARM Linux Kernel documentation - PSCI bindings
+ Documentation/devicetree/bindings/arm/psci.yaml
+
+ [3] ARM Server Base System Architecture (SBSA)
+ http://infocenter.arm.com/help/index.jsp
+
+ [4] ARM Architecture Reference Manuals
+ http://infocenter.arm.com/help/index.jsp
+
+ [6] ARM Linux Kernel documentation - Booting AArch64 Linux
+ Documentation/arm64/booting.rst
+
+properties:
+ $nodename:
+ const: idle-states
+
+ entry-method:
+ description: |
+ Usage and definition depend on ARM architecture version.
+
+ On ARM v8 64-bit this property is required.
+ On ARM 32-bit systems this property is optional
+
+ This assumes that the "enable-method" property is set to "psci" in the cpu
+ node[6] that is responsible for setting up CPU idle management in the OS
+ implementation.
+ const: psci
+
+patternProperties:
+ "^(cpu|cluster)-":
+ type: object
+ description: |
+ Each state node represents an idle state description and must be defined
+ as follows.
+
+ The idle state entered by executing the wfi instruction (idle_standby
+ SBSA,[3][4]) is considered standard on all ARM platforms and therefore
+ must not be listed.
+
+ In addition to the properties listed above, a state node may require
+ additional properties specific to the entry-method defined in the
+ idle-states node. Please refer to the entry-method bindings
+ documentation for properties definitions.
+
+ properties:
+ compatible:
+ const: arm,idle-state
+
+ local-timer-stop:
+ description:
+ If present the CPU local timer control logic is
+ lost on state entry, otherwise it is retained.
+ type: boolean
+
+ entry-latency-us:
+ description:
+ Worst case latency in microseconds required to enter the idle state.
+
+ exit-latency-us:
+ description:
+ Worst case latency in microseconds required to exit the idle state.
+ The exit-latency-us duration may be guaranteed only after
+ entry-latency-us has passed.
+
+ min-residency-us:
+ description:
+ Minimum residency duration in microseconds, inclusive of preparation
+ and entry, for this idle state to be considered worthwhile energy wise
+ (refer to section 2 of this document for a complete description).
+
+ wakeup-latency-us:
+ description: |
+ Maximum delay between the signaling of a wake-up event and the CPU
+ being able to execute normal code again. If omitted, this is assumed
+ to be equal to:
+
+ entry-latency-us + exit-latency-us
+
+ It is important to supply this value on systems where the duration of
+ PREP phase (see diagram 1, section 2) is non-neglibigle. In such
+ systems entry-latency-us + exit-latency-us will exceed
+ wakeup-latency-us by this duration.
+
+ idle-state-name:
+ $ref: /schemas/types.yaml#definitions/string
+ description:
+ A string used as a descriptive name for the idle state.
+
+ required:
+ - compatible
+ - entry-latency-us
+ - exit-latency-us
+ - min-residency-us
+
+additionalProperties: false
+
+examples:
+ - |
+
+ cpus {
+ #size-cells = <0>;
+ #address-cells = <2>;
+
+ cpu@0 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x0>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@1 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x1>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@100 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x100>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@101 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x101>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@10000 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x10000>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@10001 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x10001>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@10100 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x10100>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@10101 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a57";
+ reg = <0x0 0x10101>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_0_0 &CPU_SLEEP_0_0
+ &CLUSTER_RETENTION_0 &CLUSTER_SLEEP_0>;
+ };
+
+ cpu@100000000 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x0>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100000001 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x1>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100000100 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x100>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100000101 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x101>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100010000 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x10000>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100010001 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x10001>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100010100 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x10100>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ cpu@100010101 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a53";
+ reg = <0x1 0x10101>;
+ enable-method = "psci";
+ cpu-idle-states = <&CPU_RETENTION_1_0 &CPU_SLEEP_1_0
+ &CLUSTER_RETENTION_1 &CLUSTER_SLEEP_1>;
+ };
+
+ idle-states {
+ entry-method = "psci";
+
+ CPU_RETENTION_0_0: cpu-retention-0-0 {
+ compatible = "arm,idle-state";
+ arm,psci-suspend-param = <0x0010000>;
+ entry-latency-us = <20>;
+ exit-latency-us = <40>;
+ min-residency-us = <80>;
+ };
+
+ CLUSTER_RETENTION_0: cluster-retention-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x1010000>;
+ entry-latency-us = <50>;
+ exit-latency-us = <100>;
+ min-residency-us = <250>;
+ wakeup-latency-us = <130>;
+ };
+
+ CPU_SLEEP_0_0: cpu-sleep-0-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x0010000>;
+ entry-latency-us = <250>;
+ exit-latency-us = <500>;
+ min-residency-us = <950>;
+ };
+
+ CLUSTER_SLEEP_0: cluster-sleep-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x1010000>;
+ entry-latency-us = <600>;
+ exit-latency-us = <1100>;
+ min-residency-us = <2700>;
+ wakeup-latency-us = <1500>;
+ };
+
+ CPU_RETENTION_1_0: cpu-retention-1-0 {
+ compatible = "arm,idle-state";
+ arm,psci-suspend-param = <0x0010000>;
+ entry-latency-us = <20>;
+ exit-latency-us = <40>;
+ min-residency-us = <90>;
+ };
+
+ CLUSTER_RETENTION_1: cluster-retention-1 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x1010000>;
+ entry-latency-us = <50>;
+ exit-latency-us = <100>;
+ min-residency-us = <270>;
+ wakeup-latency-us = <100>;
+ };
+
+ CPU_SLEEP_1_0: cpu-sleep-1-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x0010000>;
+ entry-latency-us = <70>;
+ exit-latency-us = <100>;
+ min-residency-us = <300>;
+ wakeup-latency-us = <150>;
+ };
+
+ CLUSTER_SLEEP_1: cluster-sleep-1 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ arm,psci-suspend-param = <0x1010000>;
+ entry-latency-us = <500>;
+ exit-latency-us = <1200>;
+ min-residency-us = <3500>;
+ wakeup-latency-us = <1300>;
+ };
+ };
+ };
+
+ - |
+ // Example 2 (ARM 32-bit, 8-cpu system, two clusters):
+
+ cpus {
+ #size-cells = <0>;
+ #address-cells = <1>;
+
+ cpu@0 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a15";
+ reg = <0x0>;
+ cpu-idle-states = <&cpu_sleep_0_0 &cluster_sleep_0>;
+ };
+
+ cpu@1 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a15";
+ reg = <0x1>;
+ cpu-idle-states = <&cpu_sleep_0_0 &cluster_sleep_0>;
+ };
+
+ cpu@2 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a15";
+ reg = <0x2>;
+ cpu-idle-states = <&cpu_sleep_0_0 &cluster_sleep_0>;
+ };
+
+ cpu@3 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a15";
+ reg = <0x3>;
+ cpu-idle-states = <&cpu_sleep_0_0 &cluster_sleep_0>;
+ };
+
+ cpu@100 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a7";
+ reg = <0x100>;
+ cpu-idle-states = <&cpu_sleep_1_0 &cluster_sleep_1>;
+ };
+
+ cpu@101 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a7";
+ reg = <0x101>;
+ cpu-idle-states = <&cpu_sleep_1_0 &cluster_sleep_1>;
+ };
+
+ cpu@102 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a7";
+ reg = <0x102>;
+ cpu-idle-states = <&cpu_sleep_1_0 &cluster_sleep_1>;
+ };
+
+ cpu@103 {
+ device_type = "cpu";
+ compatible = "arm,cortex-a7";
+ reg = <0x103>;
+ cpu-idle-states = <&cpu_sleep_1_0 &cluster_sleep_1>;
+ };
+
+ idle-states {
+ cpu_sleep_0_0: cpu-sleep-0-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ entry-latency-us = <200>;
+ exit-latency-us = <100>;
+ min-residency-us = <400>;
+ wakeup-latency-us = <250>;
+ };
+
+ cluster_sleep_0: cluster-sleep-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ entry-latency-us = <500>;
+ exit-latency-us = <1500>;
+ min-residency-us = <2500>;
+ wakeup-latency-us = <1700>;
+ };
+
+ cpu_sleep_1_0: cpu-sleep-1-0 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ entry-latency-us = <300>;
+ exit-latency-us = <500>;
+ min-residency-us = <900>;
+ wakeup-latency-us = <600>;
+ };
+
+ cluster_sleep_1: cluster-sleep-1 {
+ compatible = "arm,idle-state";
+ local-timer-stop;
+ entry-latency-us = <800>;
+ exit-latency-us = <2000>;
+ min-residency-us = <6500>;
+ wakeup-latency-us = <2300>;
+ };
+ };
+ };
+
+...