bool "Power Management support"
depends on !IA64_HP_SIM
"Power Management" means that parts of your computer are shut
off or put into a power conserving "sleep" mode if they are not
being used. There are two competing standards for doing this: APM
and ACPI. If you want to use either one, say Y here and then also
to the requisite support below.
Power Management is most important for battery powered laptop
computers; if you have a laptop, check out the Linux Laptop home
page on the WWW at <http://www.linux-on-laptops.com/> or
Tuxmobil - Linux on Mobile Computers at <http://www.tuxmobil.org/>
and the Battery Powered Linux mini-HOWTO, available from
Note that, even if you say N here, Linux on the x86 architecture
will issue the hlt instruction if nothing is to be done, thereby
sending the processor to sleep and saving power.
bool "Power Management Debug Support"
depends on PM
This option enables various debugging support in the Power Management
code. This is helpful when debugging and reporting PM bugs, like
bool "Extra PM attributes in sysfs for low-level debugging/testing"
depends on PM_DEBUG
Add extra sysfs attributes allowing one to access some Power Management
fields of device objects from user space. If you are not a kernel
developer interested in debugging/testing Power Management, say "no".
bool "Verbose Power Management debugging"
depends on PM_DEBUG
This option enables verbose messages from the Power Management code.
depends on PM_DEBUG && PM_SLEEP && EXPERIMENTAL
This enables code to save the last PM event point across
reboot. The architecture needs to support this, x86 for
example does by saving things in the RTC, see below.
The architecture specific code must provide the extern
functions from <linux/resume-trace.h> as well as the
<asm/resume-trace.h> header with a TRACE_RESUME() macro.
The way the information is presented is architecture-
dependent, x86 will print the information during a
bool "Suspend/resume event tracing"
depends on CAN_PM_TRACE
depends on X86
This enables some cheesy code to save the last PM event point in the
RTC across reboots, so that you can debug a machine that just hangs
during suspend (or more commonly, during resume).
To use this debugging feature you should attempt to suspend the
machine, reboot it and then run
dmesg -s 1000000 | grep 'hash matches'
CAUTION: this option will cause your machine's real-time clock to be
set to an invalid time after a resume.
depends on SMP
depends on ARCH_SUSPEND_POSSIBLE || ARCH_HIBERNATION_POSSIBLE
depends on PM_SLEEP
depends on SUSPEND || HIBERNATION || XEN_SAVE_RESTORE
depends on PM_ADVANCED_DEBUG
bool "Suspend to RAM and standby"
depends on PM && ARCH_SUSPEND_POSSIBLE
select SUSPEND_NVS if HAS_IOMEM
Allow the system to enter sleep states in which main memory is
powered and thus its contents are preserved, such as the
suspend-to-RAM state (e.g. the ACPI S3 state).
bool "Test suspend/resume and wakealarm during bootup"
depends on SUSPEND && PM_DEBUG && RTC_CLASS=y
This option will let you suspend your machine during bootup, and
make it wake up a few seconds later using an RTC wakeup alarm.
Enable this with a kernel parameter like "test_suspend=mem".
You probably want to have your system's RTC driver statically
linked, ensuring that it's available when this test runs.
bool "Enable freezer for suspend to RAM/standby" \
if ARCH_WANTS_FREEZER_CONTROL || BROKEN
depends on SUSPEND
This allows you to turn off the freezer for suspend. If this is
done, no tasks are frozen for suspend to RAM/standby.
Turning OFF this setting is NOT recommended! If in doubt, say Y.
bool "Hibernation (aka 'suspend to disk')"
depends on PM && SWAP && ARCH_HIBERNATION_POSSIBLE
select SUSPEND_NVS if HAS_IOMEM
Enable the suspend to disk (STD) functionality, which is usually
called "hibernation" in user interfaces. STD checkpoints the
system and powers it off; and restores that checkpoint on reboot.
You can suspend your machine with 'echo disk > /sys/power/state'
after placing resume=/dev/swappartition on the kernel command line
in your bootloader's configuration file.
Alternatively, you can use the additional userland tools available
In principle it does not require ACPI or APM, although for example
ACPI will be used for the final steps when it is available. One
of the reasons to use software suspend is that the firmware hooks
for suspend states like suspend-to-RAM (STR) often don't work very
well with Linux.
It creates an image which is saved in your active swap. Upon the next
boot, pass the 'resume=/dev/swappartition' argument to the kernel to
have it detect the saved image, restore memory state from it, and
continue to run as before. If you do not want the previous state to
be reloaded, then use the 'noresume' kernel command line argument.
Note, however, that fsck will be run on your filesystems and you will
need to run mkswap against the swap partition used for the suspend.
It also works with swap files to a limited extent (for details see
Right now you may boot without resuming and resume later but in the
meantime you cannot use the swap partition(s)/file(s) involved in
suspending. Also in this case you must not use the filesystems
that were mounted before the suspend. In particular, you MUST NOT
MOUNT any journaled filesystems mounted before the suspend or they
will get corrupted in a nasty way.
For more information take a look at <file:Documentation/power/swsusp.txt>.
string "Default resume partition"
depends on HIBERNATION
The default resume partition is the partition that the suspend-
to-disk implementation will look for a suspended disk image.
The partition specified here will be different for almost every user.
It should be a valid swap partition (at least for now) that is turned
on before suspending.
The partition specified can be overridden by specifying:
which will set the resume partition to the device specified.
Note there is currently not a way to specify which device to save the
suspended image to. It will simply pick the first available swap
tristate "Advanced Power Management Emulation"
depends on PM && SYS_SUPPORTS_APM_EMULATION
APM is a BIOS specification for saving power using several different
techniques. This is mostly useful for battery powered laptops with
APM compliant BIOSes. If you say Y here, the system time will be
reset after a RESUME operation, the /proc/apm device will provide
battery status information, and user-space programs will receive
notification of APM "events" (e.g. battery status change).
In order to use APM, you will need supporting software. For location
and more information, read <file:Documentation/power/pm.txt> and the
Battery Powered Linux mini-HOWTO, available from
This driver does not spin down disk drives (see the hdparm(8)
manpage ("man 8 hdparm") for that), and it doesn't turn off
VESA-compliant "green" monitors.
Generally, if you don't have a battery in your machine, there isn't
much point in using this driver and you should say N. If you get
random kernel OOPSes or reboots that don't seem to be related to
anything, try disabling/enabling this option (or disabling/enabling
APM in your BIOS).
bool "Run-time PM core functionality"
depends on PM
Enable functionality allowing I/O devices to be put into energy-saving
(low power) states at run time (or autosuspended) after a specified
period of inactivity and woken up in response to a hardware-generated
wake-up event or a driver's request.
Hardware support is generally required for this functionality to work
and the bus type drivers of the buses the devices are on are
responsible for the actual handling of the autosuspend requests and
depends on PM_SLEEP || PM_RUNTIME
bool "Operating Performance Point (OPP) Layer library"
depends on PM
depends on ARCH_HAS_OPP
SOCs have a standard set of tuples consisting of frequency and
voltage pairs that the device will support per voltage domain. This
is called Operating Performance Point or OPP. The actual definitions
of OPP varies over silicon within the same family of devices.
OPP layer organizes the data internally using device pointers
representing individual voltage domains and provides SOC
implementations a ready to use framework to manage OPPs.
For more information, read <file:Documentation/power/opp.txt>