add boot partition size

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2023-12-11 d2ccde1c8e90d38cee87a1b0309ad2827f3fd30d

 kernel/Documentation/admin-guide/pm/sleep-states.rst
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+.. SPDX-License-Identifier: GPL-2.0
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+.. include:: <isonum.txt>
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+
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 ===================
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 System Sleep States
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 ===================
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-::
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+:Copyright: |copy| 2017 Intel Corporation
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- Copyright (c) 2017 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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+:Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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+
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 Sleep states are global low-power states of the entire system in which user
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 space code cannot be executed and the overall system activity is significantly
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 Basic ``sysfs`` Interfaces for System Suspend and Hibernation
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 =============================================================
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-The following files located in the :file:`/sys/power/` directory can be used by
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-user space for sleep states control.
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+The power management subsystem provides userspace with a unified ``sysfs``
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+interface for system sleep regardless of the underlying system architecture or
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+platform.  That interface is located in the :file:`/sys/power/` directory
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+(assuming that ``sysfs`` is mounted at :file:`/sys`) and it consists of the
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+following attributes (files):
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 ``state``
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 	This file contains a list of strings representing sleep states supported
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 	to start a transition of the system into the sleep state represented by
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 	that string.
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-	In particular, the strings "disk", "freeze" and "standby" represent the
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+	In particular, the "disk", "freeze" and "standby" strings represent the
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 	:ref:`hibernation <hibernation>`, :ref:`suspend-to-idle <s2idle>` and
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-	:ref:`standby <standby>` sleep states, respectively.  The string "mem"
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+	:ref:`standby <standby>` sleep states, respectively.  The "mem" string
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 	is interpreted in accordance with the contents of the ``mem_sleep`` file
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 	described below.
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 	associated with the "mem" string in the ``state`` file described above.
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 	The strings that may be present in this file are "s2idle", "shallow"
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-	and "deep".  The string "s2idle" always represents :ref:`suspend-to-idle
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+	and "deep".  The "s2idle" string always represents :ref:`suspend-to-idle
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 	<s2idle>` and, by convention, "shallow" and "deep" represent
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 	:ref:`standby <standby>` and :ref:`suspend-to-RAM <s2ram>`,
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 	respectively.
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 	Writing one of the listed strings into this file causes the system
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 	suspend variant represented by it to be associated with the "mem" string
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 	in the ``state`` file.  The string representing the suspend variant
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-	currently associated with the "mem" string in the ``state`` file
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-	is listed in square brackets.
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+	currently associated with the "mem" string in the ``state`` file is
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+	shown in square brackets.
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 	If the kernel does not support system suspend, this file is not present.
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 ``disk``
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-	This file contains a list of strings representing different operations
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-	that can be carried out after the hibernation image has been saved.  The
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-	possible options are as follows:
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+	This file controls the operating mode of hibernation (Suspend-to-Disk).
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+	Specifically, it tells the kernel what to do after creating a
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+	hibernation image.
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+	Reading from it returns a list of supported options encoded as:
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 	``platform``
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 		Put the system into a special low-power state (e.g. ACPI S4) to
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 		make additional wakeup options available and possibly allow the
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 		platform firmware to take a simplified initialization path after
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 		wakeup.
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+		It is only available if the platform provides a special
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+		mechanism to put the system to sleep after creating a
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+		hibernation image (platforms with ACPI do that as a rule, for
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+		example).
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 	``shutdown``
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 		Power off the system.
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 		the hibernation image and continue.  Otherwise, use the image
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 		to restore the previous state of the system.
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+		It is available if system suspend is supported.
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 	``test_resume``
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 		Diagnostic operation.  Load the image as though the system had
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 		just woken up from hibernation and the currently running kernel
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 		instance was a restore kernel and follow up with full system
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 		resume.
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-	Writing one of the listed strings into this file causes the option
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+	Writing one of the strings listed above into this file causes the option
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 	represented by it to be selected.
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-	The currently selected option is shown in square brackets which means
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+	The currently selected option is shown in square brackets, which means
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 	that the operation represented by it will be carried out after creating
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-	and saving the image next time hibernation is triggered by writing
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-	``disk`` to :file:`/sys/power/state`.
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+	and saving the image when hibernation is triggered by writing ``disk``
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+	to :file:`/sys/power/state`.
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 	If the kernel does not support hibernation, this file is not present.
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+
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+``image_size``
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+	This file controls the size of hibernation images.
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+
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+	It can be written a string representing a non-negative integer that will
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+	be used as a best-effort upper limit of the image size, in bytes.  The
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+	hibernation core will do its best to ensure that the image size will not
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+	exceed that number, but if that turns out to be impossible to achieve, a
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+	hibernation image will still be created and its size will be as small as
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+	possible.  In particular, writing '0' to this file causes the size of
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+	hibernation images to be minimum.
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+
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+	Reading from it returns the current image size limit, which is set to
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+	around 2/5 of the available RAM size by default.
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+
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+``pm_trace``
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+	This file controls the "PM trace" mechanism saving the last suspend
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+	or resume event point in the RTC memory across reboots.  It helps to
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+	debug hard lockups or reboots due to device driver failures that occur
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+	during system suspend or resume (which is more common) more effectively.
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+
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+	If it contains "1", the fingerprint of each suspend/resume event point
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+	in turn will be stored in the RTC memory (overwriting the actual RTC
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+	information), so it will survive a system crash if one occurs right
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+	after storing it and it can be used later to identify the driver that
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+	caused the crash to happen.
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+	It contains "0" by default, which may be changed to "1" by writing a
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+	string representing a nonzero integer into it.
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 According to the above, there are two ways to make the system go into the
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 :ref:`suspend-to-idle <s2idle>` state.  The first one is to write "freeze"
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 The default suspend variant (ie. the one to be used without writing anything
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 into :file:`/sys/power/mem_sleep`) is either "deep" (on the majority of systems
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 supporting :ref:`suspend-to-RAM <s2ram>`) or "s2idle", but it can be overridden
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-by the value of the "mem_sleep_default" parameter in the kernel command line.
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-On some ACPI-based systems, depending on the information in the ACPI tables, the
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-default may be "s2idle" even if :ref:`suspend-to-RAM <s2ram>` is supported.
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+by the value of the ``mem_sleep_default`` parameter in the kernel command line.
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+On some systems with ACPI, depending on the information in the ACPI tables, the
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+default may be "s2idle" even if :ref:`suspend-to-RAM <s2ram>` is supported in
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+principle.