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Merge tag 'pm-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/…
…git/rafael/linux-pm
Pull power management updates from Rafael Wysocki:
"This time (again) cpufreq gets the majority of changes which mostly
are driver updates (including a major consolidation of intel_pstate),
some schedutil governor modifications and core cleanups.
There also are some changes in the system suspend area, mostly related
to diagnostics and debug messages plus some renames of things related
to suspend-to-idle. One major change here is that suspend-to-idle is
now going to be preferred over S3 on systems where the ACPI tables
indicate to do so and provide requsite support (the Low Power Idle S0
_DSM in particular). The system sleep documentation and the tools
related to it are updated too.
The rest is a few cpuidle changes (nothing major), devfreq updates,
generic power domains (genpd) framework updates and a few assorted
modifications elsewhere.
Specifics:
- Drop the P-state selection algorithm based on a PID controller from
intel_pstate and make it use the same P-state selection method
(based on the CPU load) for all types of systems in the active mode
(Rafael Wysocki, Srinivas Pandruvada).
- Rework the cpufreq core and governors to make it possible to take
cross-CPU utilization updates into account and modify the schedutil
governor to actually do so (Viresh Kumar).
- Clean up the handling of transition latency information in the
cpufreq core and untangle it from the information on which drivers
cannot do dynamic frequency switching (Viresh Kumar).
- Add support for new SoCs (MT2701/MT7623 and MT7622) to the mediatek
cpufreq driver and update its DT bindings (Sean Wang).
- Modify the cpufreq dt-platdev driver to autimatically create
cpufreq devices for the new (v2) Operating Performance Points (OPP)
DT bindings and update its whitelist of supported systems (Viresh
Kumar, Shubhrajyoti Datta, Marc Gonzalez, Khiem Nguyen, Finley
Xiao).
- Add support for Ux500 to the cpufreq-dt driver and drop the
obsolete dbx500 cpufreq driver (Linus Walleij, Arnd Bergmann).
- Add new SoC (R8A7795) support to the cpufreq rcar driver (Khiem
Nguyen).
- Fix and clean up assorted issues in the cpufreq drivers and core
(Arvind Yadav, Christophe Jaillet, Colin Ian King, Gustavo Silva,
Julia Lawall, Leonard Crestez, Rob Herring, Sudeep Holla).
- Update the IO-wait boost handling in the schedutil governor to make
it less aggressive (Joel Fernandes).
- Rework system suspend diagnostics to make it print fewer messages
to the kernel log by default, add a sysfs knob to allow more
suspend-related messages to be printed and add Low Power S0 Idle
constraints checks to the ACPI suspend-to-idle code (Rafael
Wysocki, Srinivas Pandruvada).
- Prefer suspend-to-idle over S3 on ACPI-based systems with the
ACPI_FADT_LOW_POWER_S0 flag set and the Low Power Idle S0 _DSM
interface present in the ACPI tables (Rafael Wysocki).
- Update documentation related to system sleep and rename a number of
items in the code to make it cleare that they are related to
suspend-to-idle (Rafael Wysocki).
- Export a variable allowing device drivers to check the target
system sleep state from the core system suspend code (Florian
Fainelli).
- Clean up the cpuidle subsystem to handle the polling state on x86
in a more straightforward way and to use %pOF instead of full_name
(Rafael Wysocki, Rob Herring).
- Update the devfreq framework to fix and clean up a few minor issues
(Chanwoo Choi, Rob Herring).
- Extend diagnostics in the generic power domains (genpd) framework
and clean it up slightly (Thara Gopinath, Rob Herring).
- Fix and clean up a couple of issues in the operating performance
points (OPP) framework (Viresh Kumar, Waldemar Rymarkiewicz).
- Add support for RV1108 to the rockchip-io Adaptive Voltage Scaling
(AVS) driver (David Wu).
- Fix the usage of notifiers in CPU power management on some
platforms (Alex Shi).
- Update the pm-graph system suspend/hibernation and boot profiling
utility (Todd Brandt).
- Make it possible to run the cpupower utility without CPU0 (Prarit
Bhargava)"
* tag 'pm-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (87 commits)
cpuidle: Make drivers initialize polling state
cpuidle: Move polling state initialization code to separate file
cpuidle: Eliminate the CPUIDLE_DRIVER_STATE_START symbol
cpufreq: imx6q: Fix imx6sx low frequency support
cpufreq: speedstep-lib: make several arrays static, makes code smaller
PM: docs: Delete the obsolete states.txt document
PM: docs: Describe high-level PM strategies and sleep states
PM / devfreq: Fix memory leak when fail to register device
PM / devfreq: Add dependency on PM_OPP
PM / devfreq: Move private devfreq_update_stats() into devfreq
PM / devfreq: Convert to using %pOF instead of full_name
PM / AVS: rockchip-io: add io selectors and supplies for RV1108
cpufreq: ti: Fix 'of_node_put' being called twice in error handling path
cpufreq: dt-platdev: Drop few entries from whitelist
cpufreq: dt-platdev: Automatically create cpufreq device with OPP v2
ARM: ux500: don't select CPUFREQ_DT
cpuidle: Convert to using %pOF instead of full_name
cpufreq: Convert to using %pOF instead of full_name
PM / Domains: Convert to using %pOF instead of full_name
cpufreq: Cap the default transition delay value to 10 ms
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,245 @@ | ||
| =================== | ||
| System Sleep States | ||
| =================== | ||
|
|
||
| :: | ||
|
|
||
| Copyright (c) 2017 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com> | ||
|
|
||
| Sleep states are global low-power states of the entire system in which user | ||
| space code cannot be executed and the overall system activity is significantly | ||
| reduced. | ||
|
|
||
|
|
||
| Sleep States That Can Be Supported | ||
| ================================== | ||
|
|
||
| Depending on its configuration and the capabilities of the platform it runs on, | ||
| the Linux kernel can support up to four system sleep states, includig | ||
| hibernation and up to three variants of system suspend. The sleep states that | ||
| can be supported by the kernel are listed below. | ||
|
|
||
| .. _s2idle: | ||
|
|
||
| Suspend-to-Idle | ||
| --------------- | ||
|
|
||
| This is a generic, pure software, light-weight variant of system suspend (also | ||
| referred to as S2I or S2Idle). It allows more energy to be saved relative to | ||
| runtime idle by freezing user space, suspending the timekeeping and putting all | ||
| I/O devices into low-power states (possibly lower-power than available in the | ||
| working state), such that the processors can spend time in their deepest idle | ||
| states while the system is suspended. | ||
|
|
||
| The system is woken up from this state by in-band interrupts, so theoretically | ||
| any devices that can cause interrupts to be generated in the working state can | ||
| also be set up as wakeup devices for S2Idle. | ||
|
|
||
| This state can be used on platforms without support for :ref:`standby <standby>` | ||
| or :ref:`suspend-to-RAM <s2ram>`, or it can be used in addition to any of the | ||
| deeper system suspend variants to provide reduced resume latency. It is always | ||
| supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration option is set. | ||
|
|
||
| .. _standby: | ||
|
|
||
| Standby | ||
| ------- | ||
|
|
||
| This state, if supported, offers moderate, but real, energy savings, while | ||
| providing a relatively straightforward transition back to the working state. No | ||
| operating state is lost (the system core logic retains power), so the system can | ||
| go back to where it left off easily enough. | ||
|
|
||
| In addition to freezing user space, suspending the timekeeping and putting all | ||
| I/O devices into low-power states, which is done for :ref:`suspend-to-idle | ||
| <s2idle>` too, nonboot CPUs are taken offline and all low-level system functions | ||
| are suspended during transitions into this state. For this reason, it should | ||
| allow more energy to be saved relative to :ref:`suspend-to-idle <s2idle>`, but | ||
| the resume latency will generally be greater than for that state. | ||
|
|
||
| The set of devices that can wake up the system from this state usually is | ||
| reduced relative to :ref:`suspend-to-idle <s2idle>` and it may be necessary to | ||
| rely on the platform for setting up the wakeup functionality as appropriate. | ||
|
|
||
| This state is supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration | ||
| option is set and the support for it is registered by the platform with the | ||
| core system suspend subsystem. On ACPI-based systems this state is mapped to | ||
| the S1 system state defined by ACPI. | ||
|
|
||
| .. _s2ram: | ||
|
|
||
| Suspend-to-RAM | ||
| -------------- | ||
|
|
||
| This state (also referred to as STR or S2RAM), if supported, offers significant | ||
| energy savings as everything in the system is put into a low-power state, except | ||
| for memory, which should be placed into the self-refresh mode to retain its | ||
| contents. All of the steps carried out when entering :ref:`standby <standby>` | ||
| are also carried out during transitions to S2RAM. Additional operations may | ||
| take place depending on the platform capabilities. In particular, on ACPI-based | ||
| systems the kernel passes control to the platform firmware (BIOS) as the last | ||
| step during S2RAM transitions and that usually results in powering down some | ||
| more low-level components that are not directly controlled by the kernel. | ||
|
|
||
| The state of devices and CPUs is saved and held in memory. All devices are | ||
| suspended and put into low-power states. In many cases, all peripheral buses | ||
| lose power when entering S2RAM, so devices must be able to handle the transition | ||
| back to the "on" state. | ||
|
|
||
| On ACPI-based systems S2RAM requires some minimal boot-strapping code in the | ||
| platform firmware to resume the system from it. This may be the case on other | ||
| platforms too. | ||
|
|
||
| The set of devices that can wake up the system from S2RAM usually is reduced | ||
| relative to :ref:`suspend-to-idle <s2idle>` and :ref:`standby <standby>` and it | ||
| may be necessary to rely on the platform for setting up the wakeup functionality | ||
| as appropriate. | ||
|
|
||
| S2RAM is supported if the :c:macro:`CONFIG_SUSPEND` kernel configuration option | ||
| is set and the support for it is registered by the platform with the core system | ||
| suspend subsystem. On ACPI-based systems it is mapped to the S3 system state | ||
| defined by ACPI. | ||
|
|
||
| .. _hibernation: | ||
|
|
||
| Hibernation | ||
| ----------- | ||
|
|
||
| This state (also referred to as Suspend-to-Disk or STD) offers the greatest | ||
| energy savings and can be used even in the absence of low-level platform support | ||
| for system suspend. However, it requires some low-level code for resuming the | ||
| system to be present for the underlying CPU architecture. | ||
|
|
||
| Hibernation is significantly different from any of the system suspend variants. | ||
| It takes three system state changes to put it into hibernation and two system | ||
| state changes to resume it. | ||
|
|
||
| First, when hibernation is triggered, the kernel stops all system activity and | ||
| creates a snapshot image of memory to be written into persistent storage. Next, | ||
| the system goes into a state in which the snapshot image can be saved, the image | ||
| is written out and finally the system goes into the target low-power state in | ||
| which power is cut from almost all of its hardware components, including memory, | ||
| except for a limited set of wakeup devices. | ||
|
|
||
| Once the snapshot image has been written out, the system may either enter a | ||
| special low-power state (like ACPI S4), or it may simply power down itself. | ||
| Powering down means minimum power draw and it allows this mechanism to work on | ||
| any system. However, entering a special low-power state may allow additional | ||
| means of system wakeup to be used (e.g. pressing a key on the keyboard or | ||
| opening a laptop lid). | ||
|
|
||
| After wakeup, control goes to the platform firmware that runs a boot loader | ||
| which boots a fresh instance of the kernel (control may also go directly to | ||
| the boot loader, depending on the system configuration, but anyway it causes | ||
| a fresh instance of the kernel to be booted). That new instance of the kernel | ||
| (referred to as the ``restore kernel``) looks for a hibernation image in | ||
| persistent storage and if one is found, it is loaded into memory. Next, all | ||
| activity in the system is stopped and the restore kernel overwrites itself with | ||
| the image contents and jumps into a special trampoline area in the original | ||
| kernel stored in the image (referred to as the ``image kernel``), which is where | ||
| the special architecture-specific low-level code is needed. Finally, the | ||
| image kernel restores the system to the pre-hibernation state and allows user | ||
| space to run again. | ||
|
|
||
| Hibernation is supported if the :c:macro:`CONFIG_HIBERNATION` kernel | ||
| configuration option is set. However, this option can only be set if support | ||
| for the given CPU architecture includes the low-level code for system resume. | ||
|
|
||
|
|
||
| Basic ``sysfs`` Interfaces for System Suspend and Hibernation | ||
| ============================================================= | ||
|
|
||
| The following files located in the :file:`/sys/power/` directory can be used by | ||
| user space for sleep states control. | ||
|
|
||
| ``state`` | ||
| This file contains a list of strings representing sleep states supported | ||
| by the kernel. Writing one of these strings into it causes the kernel | ||
| to start a transition of the system into the sleep state represented by | ||
| that string. | ||
|
|
||
| In particular, the strings "disk", "freeze" and "standby" represent the | ||
| :ref:`hibernation <hibernation>`, :ref:`suspend-to-idle <s2idle>` and | ||
| :ref:`standby <standby>` sleep states, respectively. The string "mem" | ||
| is interpreted in accordance with the contents of the ``mem_sleep`` file | ||
| described below. | ||
|
|
||
| If the kernel does not support any system sleep states, this file is | ||
| not present. | ||
|
|
||
| ``mem_sleep`` | ||
| This file contains a list of strings representing supported system | ||
| suspend variants and allows user space to select the variant to be | ||
| associated with the "mem" string in the ``state`` file described above. | ||
|
|
||
| The strings that may be present in this file are "s2idle", "shallow" | ||
| and "deep". The string "s2idle" always represents :ref:`suspend-to-idle | ||
| <s2idle>` and, by convention, "shallow" and "deep" represent | ||
| :ref:`standby <standby>` and :ref:`suspend-to-RAM <s2ram>`, | ||
| respectively. | ||
|
|
||
| Writing one of the listed strings into this file causes the system | ||
| suspend variant represented by it to be associated with the "mem" string | ||
| in the ``state`` file. The string representing the suspend variant | ||
| currently associated with the "mem" string in the ``state`` file | ||
| is listed in square brackets. | ||
|
|
||
| If the kernel does not support system suspend, this file is not present. | ||
|
|
||
| ``disk`` | ||
| This file contains a list of strings representing different operations | ||
| that can be carried out after the hibernation image has been saved. The | ||
| possible options are as follows: | ||
|
|
||
| ``platform`` | ||
| Put the system into a special low-power state (e.g. ACPI S4) to | ||
| make additional wakeup options available and possibly allow the | ||
| platform firmware to take a simplified initialization path after | ||
| wakeup. | ||
|
|
||
| ``shutdown`` | ||
| Power off the system. | ||
|
|
||
| ``reboot`` | ||
| Reboot the system (useful for diagnostics mostly). | ||
|
|
||
| ``suspend`` | ||
| Hybrid system suspend. Put the system into the suspend sleep | ||
| state selected through the ``mem_sleep`` file described above. | ||
| If the system is successfully woken up from that state, discard | ||
| the hibernation image and continue. Otherwise, use the image | ||
| to restore the previous state of the system. | ||
|
|
||
| ``test_resume`` | ||
| Diagnostic operation. Load the image as though the system had | ||
| just woken up from hibernation and the currently running kernel | ||
| instance was a restore kernel and follow up with full system | ||
| resume. | ||
|
|
||
| Writing one of the listed strings into this file causes the option | ||
| represented by it to be selected. | ||
|
|
||
| The currently selected option is shown in square brackets which means | ||
| that the operation represented by it will be carried out after creating | ||
| and saving the image next time hibernation is triggered by writing | ||
| ``disk`` to :file:`/sys/power/state`. | ||
|
|
||
| If the kernel does not support hibernation, this file is not present. | ||
|
|
||
| According to the above, there are two ways to make the system go into the | ||
| :ref:`suspend-to-idle <s2idle>` state. The first one is to write "freeze" | ||
| directly to :file:`/sys/power/state`. The second one is to write "s2idle" to | ||
| :file:`/sys/power/mem_sleep` and then to write "mem" to | ||
| :file:`/sys/power/state`. Likewise, there are two ways to make the system go | ||
| into the :ref:`standby <standby>` state (the strings to write to the control | ||
| files in that case are "standby" or "shallow" and "mem", respectively) if that | ||
| state is supported by the platform. However, there is only one way to make the | ||
| system go into the :ref:`suspend-to-RAM <s2ram>` state (write "deep" into | ||
| :file:`/sys/power/mem_sleep` and "mem" into :file:`/sys/power/state`). | ||
|
|
||
| The default suspend variant (ie. the one to be used without writing anything | ||
| into :file:`/sys/power/mem_sleep`) is either "deep" (on the majority of systems | ||
| supporting :ref:`suspend-to-RAM <s2ram>`) or "s2idle", but it can be overridden | ||
| by the value of the "mem_sleep_default" parameter in the kernel command line. | ||
| On some ACPI-based systems, depending on the information in the ACPI tables, the | ||
| default may be "s2idle" even if :ref:`suspend-to-RAM <s2ram>` is supported. |
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