renegade-project/linux-next
2
0
Fork 0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-16 09:13:55 +08:00
Code

Documentation: admin-guide: PM: Update sleep states documentation

Browse Source 
There is some information in Documentation/power/interface.rst that
is still missing from Documentation/admin-guide/pm/sleep-states.rst
and really should be present in there, so update the latter by
adding that information to it and delete the former (as it becomes
redundant after that and it is somewhat outdated).

While at it, clean up some assorted pieces of sleep-states.rst a bit.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki 2020-01-31 11:05:17 +01:00
parent ffda81b69f
commit c21502efda
2 changed files with 59 additions and 96 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

76
Documentation/admin-guide/pm/sleep-states.rst
View File

@ -153,8 +153,11 @@ 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.
The power management subsystem provides userspace with a unified ``sysfs``
interface for system sleep regardless of the underlying system architecture or
platform. That interface is located in the :file:`/sys/power/` directory
(assuming that ``sysfs`` is mounted at :file:`/sys`) and it consists of the
following attributes (files):
``state``
This file contains a list of strings representing sleep states supported
@ -162,9 +165,9 @@ user space for sleep states control.
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
In particular, the "disk", "freeze" and "standby" strings represent the
:ref:`hibernation <hibernation>`, :ref:`suspend-to-idle <s2idle>` and
:ref:`standby <standby>` sleep states, respectively. The string "mem"
:ref:`standby <standby>` sleep states, respectively. The "mem" string
is interpreted in accordance with the contents of the ``mem_sleep`` file
described below.
@ -177,7 +180,7 @@ user space for sleep states control.
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
and "deep". The "s2idle" string always represents :ref:`suspend-to-idle
<s2idle>` and, by convention, "shallow" and "deep" represent
:ref:`standby <standby>` and :ref:`suspend-to-RAM <s2ram>`,
respectively.
@ -185,15 +188,17 @@ user space for sleep states control.
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.
currently associated with the "mem" string in the ``state`` file is
shown 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:
This file controls the operating mode of hibernation (Suspend-to-Disk).
Specifically, it tells the kernel what to do after creating a
hibernation image.
Reading from it returns a list of supported options encoded as:
``platform``
Put the system into a special low-power state (e.g. ACPI S4) to
@ -201,6 +206,11 @@ user space for sleep states control.
platform firmware to take a simplified initialization path after
wakeup.
It is only available if the platform provides a special
mechanism to put the system to sleep after creating a
hibernation image (platforms with ACPI do that as a rule, for
example).
``shutdown``
Power off the system.
@ -214,22 +224,53 @@ user space for sleep states control.
the hibernation image and continue. Otherwise, use the image
to restore the previous state of the system.
It is available if system suspend is supported.
``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
Writing one of the strings listed above into this file causes the option
represented by it to be selected.
The currently selected option is shown in square brackets which means
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`.
and saving the image when hibernation is triggered by writing ``disk``
to :file:`/sys/power/state`.
If the kernel does not support hibernation, this file is not present.
``image_size``
This file controls the size of hibernation images.
It can be written a string representing a non-negative integer that will
be used as a best-effort upper limit of the image size, in bytes. The
hibernation core will do its best to ensure that the image size will not
exceed that number, but if that turns out to be impossible to achieve, a
hibernation image will still be created and its size will be as small as
possible. In particular, writing '0' to this file causes the size of
hibernation images to be minimum.
Reading from it returns the current image size limit, which is set to
around 2/5 of the available RAM size by default.
``pm_trace``
This file controls the "PM trace" mechanism saving the last suspend
or resume event point in the RTC memory across reboots. It helps to
debug hard lockups or reboots due to device driver failures that occur
during system suspend or resume (which is more common) more effectively.
If it contains "1", the fingerprint of each suspend/resume event point
in turn will be stored in the RTC memory (overwriting the actual RTC
information), so it will survive a system crash if one occurs right
after storing it and it can be used later to identify the driver that
caused the crash to happen.
It contains "0" by default, which may be changed to "1" by writing a
string representing a nonzero integer into it.
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
@ -244,6 +285,7 @@ system go into the :ref:`suspend-to-RAM <s2ram>` state (write "deep" into
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.
by the value of the ``mem_sleep_default`` parameter in the kernel command line.
On some systems with ACPI, depending on the information in the ACPI tables, the
default may be "s2idle" even if :ref:`suspend-to-RAM <s2ram>` is supported in
principle.

79
Documentation/power/interface.rst
View File

@ -1,79 +0,0 @@
===========================================
Power Management Interface for System Sleep
===========================================
Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The power management subsystem provides userspace with a unified sysfs interface
for system sleep regardless of the underlying system architecture or platform.
The interface is located in the /sys/power/ directory (assuming that sysfs is
mounted at /sys).
/sys/power/state is the system sleep state control file.
Reading from it returns a list of supported sleep states, encoded as:
- 'freeze' (Suspend-to-Idle)
- 'standby' (Power-On Suspend)
- 'mem' (Suspend-to-RAM)
- 'disk' (Suspend-to-Disk)
Suspend-to-Idle is always supported. Suspend-to-Disk is always supported
too as long the kernel has been configured to support hibernation at all
(ie. CONFIG_HIBERNATION is set in the kernel configuration file). Support
for Suspend-to-RAM and Power-On Suspend depends on the capabilities of the
platform.
If one of the strings listed in /sys/power/state is written to it, the system
will attempt to transition into the corresponding sleep state. Refer to
Documentation/admin-guide/pm/sleep-states.rst for a description of each of
those states.
/sys/power/disk controls the operating mode of hibernation (Suspend-to-Disk).
Specifically, it tells the kernel what to do after creating a hibernation image.
Reading from it returns a list of supported options encoded as:
- 'platform' (put the system into sleep using a platform-provided method)
- 'shutdown' (shut the system down)
- 'reboot' (reboot the system)
- 'suspend' (trigger a Suspend-to-RAM transition)
- 'test_resume' (resume-after-hibernation test mode)
The currently selected option is printed in square brackets.
The 'platform' option is only available if the platform provides a special
mechanism to put the system to sleep after creating a hibernation image (ACPI
does that, for example). The 'suspend' option is available if Suspend-to-RAM
is supported. Refer to Documentation/power/basic-pm-debugging.rst for the
description of the 'test_resume' option.
To select an option, write the string representing it to /sys/power/disk.
/sys/power/image_size controls the size of hibernation images.
It can be written a string representing a non-negative integer that will be
used as a best-effort upper limit of the image size, in bytes. The hibernation
core will do its best to ensure that the image size will not exceed that number.
However, if that turns out to be impossible to achieve, a hibernation image will
still be created and its size will be as small as possible. In particular,
writing '0' to this file will enforce hibernation images to be as small as
possible.
Reading from this file returns the current image size limit, which is set to
around 2/5 of available RAM by default.
/sys/power/pm_trace controls the PM trace mechanism saving the last suspend
or resume event point in the RTC across reboots.
It helps to debug hard lockups or reboots due to device driver failures that
occur during system suspend or resume (which is more common) more effectively.
If /sys/power/pm_trace contains '1', the fingerprint of each suspend/resume
event point in turn will be stored in the RTC memory (overwriting the actual
RTC information), so it will survive a system crash if one occurs right after
storing it and it can be used later to identify the driver that caused the crash
to happen (see Documentation/power/s2ram.rst for more information).
Initially it contains '0' which may be changed to '1' by writing a string
representing a nonzero integer into it.