How to make ACPI work

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General

First, simply try using the power management features of Linux on your computer. Tell Linux to suspend (System > Preferences > Power Management in Gnome). Try closing the lid. ACPI may already work.

Update BIOS

ACPI requires a relatively new BIOS version. In particular, if you get the message, 

  ACPI: Could not use ECDT

during startup, you probably need a BIOS Upgrade. For example, a BIOS upgrade from version 1.02 to 1.10 was all that was needed for ACPI to start working on an A31 2652 running Red Hat Enterprise Linux 5 (CentOS 5).

Kernel configuration

Many Kernel 2.6 distributions like Red Hat Enterprise Linux 5 (Centos 5) have ACPI built in and ready to go. If not, you must enable ACPI support in your kernel.

To do this open your kernel config and enable ACPI Power Management:

Power management options → <*>Power Management support (CONFIG_PM)
Power management options → <*>ACPI Support (CONFIG_ACPI)

You'd most likely want to enable the following ACPI options:

Power management options → <*>Suspend to RAM and standby (CONFIG_SUSPEND)
Power management options → ACPI → <*>AC Adapter (CONFIG_ACPI_AC)
Power management options → ACPI → <*>Battery (CONFIG_ACPI_BATTERY)
Power management options → ACPI → <*>Button (CONFIG_ACPI_BUTTON)
Power management options → ACPI → <*>Fan (CONFIG_ACPI_FAN)
Power management options → ACPI → <*>Processor (CONFIG_ACPI_PROCESSOR)
Power management options → ACPI → <*>Thermal Zone (CONFIG_ACPI_THERMAL)

If you prefer editing your .config file directly, you should set at least the following variables: 

CONFIG_PM=y
CONFIG_ACPI=y
CONFIG_ACPI_AC=y
CONFIG_ACPI_BATTERY=y
CONFIG_ACPI_BUTTON=y
CONFIG_ACPI_FAN=y
CONFIG_ACPI_PROCESSOR=y
CONFIG_ACPI_THERMAL=y
CONFIG_ACPI_BLACKLIRG_YEAR=0
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_SYSTEM=y

Then recompile your kernel.

Hint:
ACPI SLEEP States option did only show up for me after patching Software Suspend 2 into the kernel. With a vanilla 2.6.17 kernel, one must enable CONFIG_SMP and CONFIG_HOTPLUG_CPU for the option to appear, cf. Debian bug #383059 .

(This should be fixed in 2.6.23, there are new CONFIG_SUSPEND and CONFIG_HIBERNATION config options)

Kernel boot parameters

Many ThinkPads have been hit by a recent (kernel 2.6.16) change to ACPI4Linux that changed the default means of accessing the ACPI Embedded Controller as a way to shake out underlying bugs in the EC access code. If your ThinkPad fails to resume properly (a blinking Sleep light on resume that doesn't go away, or a hang when trying to suspend/standby a second time), adding ec_intr=0 to your kernel command line may help.

IBM specific ACPI driver

Pre-2.6.22

Unfortunately, special drivers for ACPI on ThinkPads were not included with kernels prior 2.6.10. So you'll have to compile one yourself or get it as precompiled module for your kernel.

You have the choice between thinkpad-acpi and ibm-acpi, with the latter being the recommended one.

If you use a post-2.6.10 kernel and you want to use ibm-acpi, it is recommended to look on its projects page for a possibly newer version.

Post-2.6.22

If you are using kernel version 2.6.22 and higher, you have only one choce, ibm-acpi, which has been renamed to thinkpad-acpi.

Hint:
Generally it is a good idea to read the README included with the driver.

Backlight problems with post-2.6.26 kernels

According to [this thread], users with 2.6.26 kernel and higher may experience problems with ThinkPad backlight contols (Fn+Home, Fn+End on T61). The symptoms are:

  • backlight brightness controls do not work;
  • Using acpi-listen command, there is no reaction for brightness down button, but brightenss up gives:
 ibm/hotkey HKEY 00000080 00001010

The solution is that one needs to enable `CONFIG_VIDEO_OUTPUT_CONTROL`: 

Device Drivers  --->
  Graphics Support  --->
    <*> Lowlevel video output switch controls

Subsequently one should enable 'CONFIG_ACPI_VIDEO': 

Power Management Options  --->
  [*] ACPI (Advanced Configuration and Power Interface) Support  --->
    <*> Video
NOTE!
Without `CONFIG_VIDEO_OUTPUT_CONTROL` enabled, one will not be able to enable `CONFIG_ACPI_VIDEO` in menuconfig or similar interface as the option will remain hidden

ACPI daemon

Also you'll need to install acpid, if it isn't present on your system. acpid is a daemon that handles the ACPI events generated by the system. Read How to configure acpid.

NOTE!
For acpid to work, the ACPI event interface /proc/acpi/event must be configured in the kernel (via CONFIG_ACPI_PROC_EVENT). As of kernel 2.6.25, this interface is deprecated. ACPI events are now distributed through the kernel's input event framework, making acpid redundant and, ultimately, obsolete. However, userspace utilities have been slow to migrate toward the new interface, and many Linux distributions continue to enable the old interface. Check your kernel configuration, or check to see if /proc/acpi/event exists.

Screen blanking (Standby)

Make sure you have 

Option "DPMS"

in the Monitor section of your /etc/X11/XF86Config or /etc/X11/xorg.conf.

Running $ xset +dpms and then $ xset dpms force off will turn off the backlight on a laptop screen.

Note that this may not work in combination with $ echo -n "mem" > /sys/power/state because switching to console causes the backlight to come back on before sleeping.

Suspend to RAM (Sleep)

ACPI Sleep/suspend-to-ram with recent 2.6.x kernels usually works fine. Have a look at the acpid configuration HOWTO. It includes a specific example for going to sleep on lid close.

For Troubleshooting, look at the Problems with ACPI suspend-to-ram page.

Suspend to disk (Hibernate)

There are two drivers for this available:

  • swsusp, which is in the kernel and
  • TuxOnIce which is more feature rich, but not yet in the kernel, so you have to patch it in yourself.

Both are reported to work fine as long as you use open-source graphic drivers. A comparison of the features can be found on this page.

Just in case you are in doubt...yes, it is safe in both cases to use the same swap partition as active swap and as suspend partition.

See the according drivers page for instructions.

ThinkPads on which it is recommended to use ACPI

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