Documentation/laptops/thinkpad-acpi.txt

		     ThinkPad ACPI Extras Driver

                            Version 0.25
                        October 16th,  2013

               Borislav Deianov <borislav@users.sf.net>
             Henrique de Moraes Holschuh <hmh@hmh.eng.br>
                      http://ibm-acpi.sf.net/


This is a Linux driver for the IBM and Lenovo ThinkPad laptops. It
supports various features of these laptops which are accessible
through the ACPI and ACPI EC framework, but not otherwise fully
supported by the generic Linux ACPI drivers.

This driver used to be named ibm-acpi until kernel 2.6.21 and release
0.13-20070314.  It used to be in the drivers/acpi tree, but it was
moved to the drivers/misc tree and renamed to thinkpad-acpi for kernel
2.6.22, and release 0.14.  It was moved to drivers/platform/x86 for
kernel 2.6.29 and release 0.22.

The driver is named "thinkpad-acpi".  In some places, like module
names and log messages, "thinkpad_acpi" is used because of userspace
issues.

"tpacpi" is used as a shorthand where "thinkpad-acpi" would be too
long due to length limitations on some Linux kernel versions.

Status
------

The features currently supported are the following (see below for
detailed description):

	- Fn key combinations
	- Bluetooth enable and disable
	- video output switching, expansion control
	- ThinkLight on and off
	- CMOS/UCMS control
	- LED control
	- ACPI sounds
	- temperature sensors
	- Experimental: embedded controller register dump
	- LCD brightness control
	- Volume control
	- Fan control and monitoring: fan speed, fan enable/disable
	- WAN enable and disable
	- UWB enable and disable

A compatibility table by model and feature is maintained on the web
site, http://ibm-acpi.sf.net/. I appreciate any success or failure
reports, especially if they add to or correct the compatibility table.
Please include the following information in your report:

	- ThinkPad model name
	- a copy of your ACPI tables, using the "acpidump" utility
	- a copy of the output of dmidecode, with serial numbers
	  and UUIDs masked off
	- which driver features work and which don't
	- the observed behavior of non-working features

Any other comments or patches are also more than welcome.


Installation
------------

If you are compiling this driver as included in the Linux kernel
sources, look for the CONFIG_THINKPAD_ACPI Kconfig option.
It is located on the menu path: "Device Drivers" -> "X86 Platform
Specific Device Drivers" -> "ThinkPad ACPI Laptop Extras".


Features
--------

The driver exports two different interfaces to userspace, which can be
used to access the features it provides.  One is a legacy procfs-based
interface, which will be removed at some time in the future.  The other
is a new sysfs-based interface which is not complete yet.

The procfs interface creates the /proc/acpi/ibm directory.  There is a
file under that directory for each feature it supports.  The procfs
interface is mostly frozen, and will change very little if at all: it
will not be extended to add any new functionality in the driver, instead
all new functionality will be implemented on the sysfs interface.

The sysfs interface tries to blend in the generic Linux sysfs subsystems
and classes as much as possible.  Since some of these subsystems are not
yet ready or stabilized, it is expected that this interface will change,
and any and all userspace programs must deal with it.


Notes about the sysfs interface:

Unlike what was done with the procfs interface, correctness when talking
to the sysfs interfaces will be enforced, as will correctness in the
thinkpad-acpi's implementation of sysfs interfaces.

Also, any bugs in the thinkpad-acpi sysfs driver code or in the
thinkpad-acpi's implementation of the sysfs interfaces will be fixed for
maximum correctness, even if that means changing an interface in
non-compatible ways.  As these interfaces mature both in the kernel and
in thinkpad-acpi, such changes should become quite rare.

Applications interfacing to the thinkpad-acpi sysfs interfaces must
follow all sysfs guidelines and correctly process all errors (the sysfs
interface makes extensive use of errors).  File descriptors and open /
close operations to the sysfs inodes must also be properly implemented.

The version of thinkpad-acpi's sysfs interface is exported by the driver
as a driver attribute (see below).

Sysfs driver attributes are on the driver's sysfs attribute space,
for 2.6.23+ this is /sys/bus/platform/drivers/thinkpad_acpi/ and
/sys/bus/platform/drivers/thinkpad_hwmon/

Sysfs device attributes are on the thinkpad_acpi device sysfs attribute
space, for 2.6.23+ this is /sys/devices/platform/thinkpad_acpi/.

Sysfs device attributes for the sensors and fan are on the
thinkpad_hwmon device's sysfs attribute space, but you should locate it
looking for a hwmon device with the name attribute of "thinkpad", or
better yet, through libsensors.


Driver version
--------------

procfs: /proc/acpi/ibm/driver
sysfs driver attribute: version

The driver name and version. No commands can be written to this file.


Sysfs interface version
-----------------------

sysfs driver attribute: interface_version

Version of the thinkpad-acpi sysfs interface, as an unsigned long
(output in hex format: 0xAAAABBCC), where:
	AAAA - major revision
	BB - minor revision
	CC - bugfix revision

The sysfs interface version changelog for the driver can be found at the
end of this document.  Changes to the sysfs interface done by the kernel
subsystems are not documented here, nor are they tracked by this
attribute.

Changes to the thinkpad-acpi sysfs interface are only considered
non-experimental when they are submitted to Linux mainline, at which
point the changes in this interface are documented and interface_version
may be updated.  If you are using any thinkpad-acpi features not yet
sent to mainline for merging, you do so on your own risk: these features
may disappear, or be implemented in a different and incompatible way by
the time they are merged in Linux mainline.

Changes that are backwards-compatible by nature (e.g. the addition of
attributes that do not change the way the other attributes work) do not
always warrant an update of interface_version.  Therefore, one must
expect that an attribute might not be there, and deal with it properly
(an attribute not being there *is* a valid way to make it clear that a
feature is not available in sysfs).


Hot keys
--------

procfs: /proc/acpi/ibm/hotkey
sysfs device attribute: hotkey_*

In a ThinkPad, the ACPI HKEY handler is responsible for communicating
some important events and also keyboard hot key presses to the operating
system.  Enabling the hotkey functionality of thinkpad-acpi signals the
firmware that such a driver is present, and modifies how the ThinkPad
firmware will behave in many situations.

The driver enables the HKEY ("hot key") event reporting automatically
when loaded, and disables it when it is removed.

The driver will report HKEY events in the following format:

	ibm/hotkey HKEY 00000080 0000xxxx

Some of these events refer to hot key presses, but not all of them.

The driver will generate events over the input layer for hot keys and
radio switches, and over the ACPI netlink layer for other events.  The
input layer support accepts the standard IOCTLs to remap the keycodes
assigned to each hot key.

The hot key bit mask allows some control over which hot keys generate
events.  If a key is "masked" (bit set to 0 in the mask), the firmware
will handle it.  If it is "unmasked", it signals the firmware that
thinkpad-acpi would prefer to handle it, if the firmware would be so
kind to allow it (and it often doesn't!).

Not all bits in the mask can be modified.  Not all bits that can be
modified do anything.  Not all hot keys can be individually controlled
by the mask.  Some models do not support the mask at all.  The behaviour
of the mask is, therefore, highly dependent on the ThinkPad model.

The driver will filter out any unmasked hotkeys, so even if the firmware
doesn't allow disabling an specific hotkey, the driver will not report
events for unmasked hotkeys.

Note that unmasking some keys prevents their default behavior.  For
example, if Fn+F5 is unmasked, that key will no longer enable/disable
Bluetooth by itself in firmware.

Note also that not all Fn key combinations are supported through ACPI
depending on the ThinkPad model and firmware version.  On those
ThinkPads, it is still possible to support some extra hotkeys by
polling the "CMOS NVRAM" at least 10 times per second.  The driver
attempts to enables this functionality automatically when required.

procfs notes:

The following commands can be written to the /proc/acpi/ibm/hotkey file:

	echo 0xffffffff > /proc/acpi/ibm/hotkey -- enable all hot keys
	echo 0 > /proc/acpi/ibm/hotkey -- disable all possible hot keys
	... any other 8-hex-digit mask ...
	echo reset > /proc/acpi/ibm/hotkey -- restore the recommended mask

The following commands have been deprecated and will cause the kernel
to log a warning:

	echo enable > /proc/acpi/ibm/hotkey -- does nothing
	echo disable > /proc/acpi/ibm/hotkey -- returns an error

The procfs interface does not support NVRAM polling control.  So as to
maintain maximum bug-to-bug compatibility, it does not report any masks,
nor does it allow one to manipulate the hot key mask when the firmware
does not support masks at all, even if NVRAM polling is in use.

sysfs notes:

	hotkey_bios_enabled:
		DEPRECATED, WILL BE REMOVED SOON.

		Returns 0.

	hotkey_bios_mask:
		DEPRECATED, DON'T USE, WILL BE REMOVED IN THE FUTURE.

		Returns the hot keys mask when thinkpad-acpi was loaded.
		Upon module unload, the hot keys mask will be restored
		to this value.   This is always 0x80c, because those are
		the hotkeys that were supported by ancient firmware
		without mask support.

	hotkey_enable:
		DEPRECATED, WILL BE REMOVED SOON.

		0: returns -EPERM
		1: does nothing

	hotkey_mask:
		bit mask to enable reporting (and depending on
		the firmware, ACPI event generation) for each hot key
		(see above).  Returns the current status of the hot keys
		mask, and allows one to modify it.

	hotkey_all_mask:
		bit mask that should enable event reporting for all
		supported hot keys, when echoed to hotkey_mask above.
		Unless you know which events need to be handled
		passively (because the firmware *will* handle them
		anyway), do *not* use hotkey_all_mask.  Use
		hotkey_recommended_mask, instead. You have been warned.

	hotkey_recommended_mask:
		bit mask that should enable event reporting for all
		supported hot keys, except those which are always
		handled by the firmware anyway.  Echo it to
		hotkey_mask above, to use.  This is the default mask
		used by the driver.

	hotkey_source_mask:
		bit mask that selects which hot keys will the driver
		poll the NVRAM for.  This is auto-detected by the driver
		based on the capabilities reported by the ACPI firmware,
		but it can be overridden at runtime.

		Hot keys whose bits are set in hotkey_source_mask are
		polled for in NVRAM, and reported as hotkey events if
		enabled in hotkey_mask.  Only a few hot keys are
		available through CMOS NVRAM polling.

		Warning: when in NVRAM mode, the volume up/down/mute
		keys are synthesized according to changes in the mixer,
		which uses a single volume up or volume down hotkey
		press to unmute, as per the ThinkPad volume mixer user
		interface.  When in ACPI event mode, volume up/down/mute
		events are reported by the firmware and can behave
		differently (and that behaviour changes with firmware
		version -- not just with firmware models -- as well as
		OSI(Linux) state).

	hotkey_poll_freq:
		frequency in Hz for hot key polling. It must be between
		0 and 25 Hz.  Polling is only carried out when strictly
		needed.

		Setting hotkey_poll_freq to zero disables polling, and
		will cause hot key presses that require NVRAM polling
		to never be reported.

		Setting hotkey_poll_freq too low may cause repeated
		pressings of the same hot key to be misreported as a
		single key press, or to not even be detected at all.
		The recommended polling frequency is 10Hz.

	hotkey_radio_sw:
		If the ThinkPad has a hardware radio switch, this
		attribute will read 0 if the switch is in the "radios
		disabled" position, and 1 if the switch is in the
		"radios enabled" position.

		This attribute has poll()/select() support.

	hotkey_tablet_mode:
		If the ThinkPad has tablet capabilities, this attribute
		will read 0 if the ThinkPad is in normal mode, and
		1 if the ThinkPad is in tablet mode.

		This attribute has poll()/select() support.

	wakeup_reason:
		Set to 1 if the system is waking up because the user
		requested a bay ejection.  Set to 2 if the system is
		waking up because the user requested the system to
		undock.  Set to zero for normal wake-ups or wake-ups
		due to unknown reasons.

		This attribute has poll()/select() support.

	wakeup_hotunplug_complete:
		Set to 1 if the system was waken up because of an
		undock or bay ejection request, and that request
		was successfully completed.  At this point, it might
		be useful to send the system back to sleep, at the
		user's choice.  Refer to HKEY events 0x4003 and
		0x3003, below.

		This attribute has poll()/select() support.

input layer notes:

A Hot key is mapped to a single input layer EV_KEY event, possibly
followed by an EV_MSC MSC_SCAN event that shall contain that key's scan
code.  An EV_SYN event will always be generated to mark the end of the
event block.

Do not use the EV_MSC MSC_SCAN events to process keys.  They are to be
used as a helper to remap keys, only.  They are particularly useful when
remapping KEY_UNKNOWN keys.

The events are available in an input device, with the following id:

	Bus:		BUS_HOST
	vendor:		0x1014 (PCI_VENDOR_ID_IBM)  or
			0x17aa (PCI_VENDOR_ID_LENOVO)
	product:	0x5054 ("TP")
	version:	0x4101

The version will have its LSB incremented if the keymap changes in a
backwards-compatible way.  The MSB shall always be 0x41 for this input
device.  If the MSB is not 0x41, do not use the device as described in
this section, as it is either something else (e.g. another input device
exported by a thinkpad driver, such as HDAPS) or its functionality has
been changed in a non-backwards compatible way.

Adding other event types for other functionalities shall be considered a
backwards-compatible change for this input device.

Thinkpad-acpi Hot Key event map (version 0x4101):

ACPI	Scan
event	code	Key		Notes

0x1001	0x00	FN+F1		-

0x1002	0x01	FN+F2		IBM: battery (rare)
				Lenovo: Screen lock

0x1003	0x02	FN+F3		Many IBM models always report
				this hot key, even with hot keys
				disabled or with Fn+F3 masked
				off
				IBM: screen lock, often turns
				off the ThinkLight as side-effect
				Lenovo: battery

0x1004	0x03	FN+F4		Sleep button (ACPI sleep button
				semantics, i.e. sleep-to-RAM).
				It always generates some kind
				of event, either the hot key
				event or an ACPI sleep button
				event. The firmware may
				refuse to generate further FN+F4
				key presses until a S3 or S4 ACPI
				sleep cycle is performed or some
				time passes.

0x1005	0x04	FN+F5		Radio.  Enables/disables
				the internal Bluetooth hardware
				and W-WAN card if left in control
				of the firmware.  Does not affect
				the WLAN card.
				Should be used to turn on/off all
				radios (Bluetooth+W-WAN+WLAN),
				really.

0x1006	0x05	FN+F6		-

0x1007	0x06	FN+F7		Video output cycle.
				Do you feel lucky today?

0x1008	0x07	FN+F8		IBM: toggle screen expand
				Lenovo: configure UltraNav,
				or toggle screen expand

0x1009	0x08	FN+F9		-
	..	..		..
0x100B	0x0A	FN+F11		-

0x100C	0x0B	FN+F12		Sleep to disk.  You are always
				supposed to handle it yourself,
				either through the ACPI event,
				or through a hotkey event.
				The firmware may refuse to
				generate further FN+F12 key
				press events until a S3 or S4
				ACPI sleep cycle is performed,
				or some time passes.

0x100D	0x0C	FN+BACKSPACE	-
0x100E	0x0D	FN+INSERT	-
0x100F	0x0E	FN+DELETE	-

0x1010	0x0F	FN+HOME		Brightness up.  This key is
				always handled by the firmware
				in IBM ThinkPads, even when
				unmasked.  Just leave it alone.
				For Lenovo ThinkPads with a new
				BIOS, it has to be handled either
				by the ACPI OSI, or by userspace.
				The driver does the right thing,
				never mess with this.
0x1011	0x10	FN+END		Brightness down.  See brightness
				up for details.

0x1012	0x11	FN+PGUP		ThinkLight toggle.  This key is
				always handled by the firmware,
				even when unmasked.

0x1013	0x12	FN+PGDOWN	-

0x1014	0x13	FN+SPACE	Zoom key

0x1015	0x14	VOLUME UP	Internal mixer volume up. This
				key is always handled by the
				firmware, even when unmasked.
				NOTE: Lenovo seems to be changing
				this.
0x1016	0x15	VOLUME DOWN	Internal mixer volume up. This
				key is always handled by the
				firmware, even when unmasked.
				NOTE: Lenovo seems to be changing
				this.
0x1017	0x16	MUTE		Mute internal mixer. This
				key is always handled by the
				firmware, even when unmasked.

0x1018	0x17	THINKPAD	ThinkPad/Access IBM/Lenovo key

0x1019	0x18	unknown
..	..	..
0x1020	0x1F	unknown

The ThinkPad firmware does not allow one to differentiate when most hot
keys are pressed or released (either that, or we don't know how to, yet).
For these keys, the driver generates a set of events for a key press and
immediately issues the same set of events for a key release.  It is
unknown by the driver if the ThinkPad firmware triggered these events on
hot key press or release, but the firmware will do it for either one, not
both.

If a key is mapped to KEY_RESERVED, it generates no input events at all.
If a key is mapped to KEY_UNKNOWN, it generates an input event that
includes an scan code.  If a key is mapped to anything else, it will
generate input device EV_KEY events.

In addition to the EV_KEY events, thinkpad-acpi may also issue EV_SW
events for switches:

SW_RFKILL_ALL	T60 and later hardware rfkill rocker switch
SW_TABLET_MODE	Tablet ThinkPads HKEY events 0x5009 and 0x500A

Non hotkey ACPI HKEY event map:
-------------------------------

Events that are never propagated by the driver:

0x2304		System is waking up from suspend to undock
0x2305		System is waking up from suspend to eject bay
0x2404		System is waking up from hibernation to undock
0x2405		System is waking up from hibernation to eject bay
0x5001		Lid closed
0x5002		Lid opened
0x5009		Tablet swivel: switched to tablet mode
0x500A		Tablet swivel: switched to normal mode
0x5010		Brightness level changed/control event
0x6000		KEYBOARD: Numlock key pressed
0x6005		KEYBOARD: Fn key pressed (TO BE VERIFIED)
0x7000		Radio Switch may have changed state


Events that are propagated by the driver to userspace:

0x2313		ALARM: System is waking up from suspend because
		the battery is nearly empty
0x2413		ALARM: System is waking up from hibernation because
		the battery is nearly empty
0x3003		Bay ejection (see 0x2x05) complete, can sleep again
0x3006		Bay hotplug request (hint to power up SATA link when
		the optical drive tray is ejected)
0x4003		Undocked (see 0x2x04), can sleep again
0x4010		Docked into hotplug port replicator (non-ACPI dock)
0x4011		Undocked from hotplug port replicator (non-ACPI dock)
0x500B		Tablet pen inserted into its storage bay
0x500C		Tablet pen removed from its storage bay
0x6011		ALARM: battery is too hot
0x6012		ALARM: battery is extremely hot
0x6021		ALARM: a sensor is too hot
0x6022		ALARM: a sensor is extremely hot
0x6030		System thermal table changed
0x6040		Nvidia Optimus/AC adapter related (TO BE VERIFIED)

Battery nearly empty alarms are a last resort attempt to get the
operating system to hibernate or shutdown cleanly (0x2313), or shutdown
cleanly (0x2413) before power is lost.  They must be acted upon, as the
wake up caused by the firmware will have negated most safety nets...

When any of the "too hot" alarms happen, according to Lenovo the user
should suspend or hibernate the laptop (and in the case of battery
alarms, unplug the AC adapter) to let it cool down.  These alarms do
signal that something is wrong, they should never happen on normal
operating conditions.

The "extremely hot" alarms are emergencies.  According to Lenovo, the
operating system is to force either an immediate suspend or hibernate
cycle, or a system shutdown.  Obviously, something is very wrong if this
happens.


Brightness hotkey notes:

Don't mess with the brightness hotkeys in a Thinkpad.  If you want
notifications for OSD, use the sysfs backlight class event support.

The driver will issue KEY_BRIGHTNESS_UP and KEY_BRIGHTNESS_DOWN events
automatically for the cases were userspace has to do something to
implement brightness changes.  When you override these events, you will
either fail to handle properly the ThinkPads that require explicit
action to change backlight brightness, or the ThinkPads that require
that no action be taken to work properly.


Bluetooth
---------

procfs: /proc/acpi/ibm/bluetooth
sysfs device attribute: bluetooth_enable (deprecated)
sysfs rfkill class: switch "tpacpi_bluetooth_sw"

This feature shows the presence and current state of a ThinkPad
Bluetooth device in the internal ThinkPad CDC slot.

If the ThinkPad supports it, the Bluetooth state is stored in NVRAM,
so it is kept across reboots and power-off.

Procfs notes:

If Bluetooth is installed, the following commands can be used:

	echo enable > /proc/acpi/ibm/bluetooth
	echo disable > /proc/acpi/ibm/bluetooth

Sysfs notes:

	If the Bluetooth CDC card is installed, it can be enabled /
	disabled through the "bluetooth_enable" thinkpad-acpi device
	attribute, and its current status can also be queried.

	enable:
		0: disables Bluetooth / Bluetooth is disabled
		1: enables Bluetooth / Bluetooth is enabled.

	Note: this interface has been superseded by the	generic rfkill
	class.  It has been deprecated, and it will be removed in year
	2010.

	rfkill controller switch "tpacpi_bluetooth_sw": refer to
	Documentation/rfkill.txt for details.


Video output control -- /proc/acpi/ibm/video
--------------------------------------------

This feature allows control over the devices used for video output -
LCD, CRT or DVI (if available). The following commands are available:

	echo lcd_enable > /proc/acpi/ibm/video
	echo lcd_disable > /proc/acpi/ibm/video
	echo crt_enable > /proc/acpi/ibm/video
	echo crt_disable > /proc/acpi/ibm/video
	echo dvi_enable > /proc/acpi/ibm/video
	echo dvi_disable > /proc/acpi/ibm/video
	echo auto_enable > /proc/acpi/ibm/video
	echo auto_disable > /proc/acpi/ibm/video
	echo expand_toggle > /proc/acpi/ibm/video
	echo video_switch > /proc/acpi/ibm/video

NOTE: Access to this feature is restricted to processes owning the
CAP_SYS_ADMIN capability for safety reasons, as it can interact badly
enough with some versions of X.org to crash it.

Each video output device can be enabled or disabled individually.
Reading /proc/acpi/ibm/video shows the status of each device.

Automatic video switching can be enabled or disabled.  When automatic
video switching is enabled, certain events (e.g. opening the lid,
docking or undocking) cause the video output device to change
automatically. While this can be useful, it also causes flickering
and, on the X40, video corruption. By disabling automatic switching,
the flickering or video corruption can be avoided.

The video_switch command cycles through the available video outputs
(it simulates the behavior of Fn-F7).

Video expansion can be toggled through this feature. This controls
whether the display is expanded to fill the entire LCD screen when a
mode with less than full resolution is used. Note that the current
video expansion status cannot be determined through this feature.

Note that on many models (particularly those using Radeon graphics
chips) the X driver configures the video card in a way which prevents
Fn-F7 from working. This also disables the video output switching
features of this driver, as it uses the same ACPI methods as
Fn-F7. Video switching on the console should still work.

UPDATE: refer to https://bugs.freedesktop.org/show_bug.cgi?id=2000


ThinkLight control
------------------

procfs: /proc/acpi/ibm/light
sysfs attributes: as per LED class, for the "tpacpi::thinklight" LED

procfs notes:

The ThinkLight status can be read and set through the procfs interface.  A
few models which do not make the status available will show the ThinkLight
status as "unknown". The available commands are:

	echo on  > /proc/acpi/ibm/light
	echo off > /proc/acpi/ibm/light

sysfs notes:

The ThinkLight sysfs interface is documented by the LED class
documentation, in Documentation/leds/leds-class.txt.  The ThinkLight LED name
is "tpacpi::thinklight".

Due to limitations in the sysfs LED class, if the status of the ThinkLight
cannot be read or if it is unknown, thinkpad-acpi will report it as "off".
It is impossible to know if the status returned through sysfs is valid.


CMOS/UCMS control
-----------------

procfs: /proc/acpi/ibm/cmos
sysfs device attribute: cmos_command

This feature is mostly used internally by the ACPI firmware to keep the legacy
CMOS NVRAM bits in sync with the current machine state, and to record this
state so that the ThinkPad will retain such settings across reboots.

Some of these commands actually perform actions in some ThinkPad models, but
this is expected to disappear more and more in newer models.  As an example, in
a T43 and in a X40, commands 12 and 13 still control the ThinkLight state for
real, but commands 0 to 2 don't control the mixer anymore (they have been
phased out) and just update the NVRAM.

The range of valid cmos command numbers is 0 to 21, but not all have an
effect and the behavior varies from model to model.  Here is the behavior
on the X40 (tpb is the ThinkPad Buttons utility):

	0 - Related to "Volume down" key press
	1 - Related to "Volume up" key press
	2 - Related to "Mute on" key press
	3 - Related to "Access IBM" key press
	4 - Related to "LCD brightness up" key press
	5 - Related to "LCD brightness down" key press
	11 - Related to "toggle screen expansion" key press/function
	12 - Related to "ThinkLight on"
	13 - Related to "ThinkLight off"
	14 - Related to "ThinkLight" key press (toggle ThinkLight)

The cmos command interface is prone to firmware split-brain problems, as
in newer ThinkPads it is just a compatibility layer.  Do not use it, it is
exported just as a debug tool.


LED control
-----------

procfs: /proc/acpi/ibm/led
sysfs attributes: as per LED class, see below for names

Some of the LED indicators can be controlled through this feature.  On
some older ThinkPad models, it is possible to query the status of the
LED indicators as well.  Newer ThinkPads cannot query the real status
of the LED indicators.

Because misuse of the LEDs could induce an unaware user to perform
dangerous actions (like undocking or ejecting a bay device while the
buses are still active), or mask an important alarm (such as a nearly
empty battery, or a broken battery), access to most LEDs is
restricted.

Unrestricted access to all LEDs requires that thinkpad-acpi be
compiled with the CONFIG_THINKPAD_ACPI_UNSAFE_LEDS option enabled.
Distributions must never enable this option.  Individual users that
are aware of the consequences are welcome to enabling it.

Audio mute and microphone mute LEDs are supported, but currently not
visible to userspace. They are used by the snd-hda-intel audio driver.

procfs notes:

The available commands are:

	echo '<LED number> on' >/proc/acpi/ibm/led
	echo '<LED number> off' >/proc/acpi/ibm/led
	echo '<LED number> blink' >/proc/acpi/ibm/led

The <LED number> range is 0 to 15. The set of LEDs that can be
controlled varies from model to model. Here is the common ThinkPad
mapping:

	0 - power
	1 - battery (orange)
	2 - battery (green)
	3 - UltraBase/dock
	4 - UltraBay
	5 - UltraBase battery slot
	6 - (unknown)
	7 - standby
	8 - dock status 1
	9 - dock status 2
	10, 11 - (unknown)
	12 - thinkvantage
	13, 14, 15 - (unknown)

All of the above can be turned on and off and can be made to blink.

sysfs notes:

The ThinkPad LED sysfs interface is described in detail by the LED class
documentation, in Documentation/leds/leds-class.txt.

The LEDs are named (in LED ID order, from 0 to 12):
"tpacpi::power", "tpacpi:orange:batt", "tpacpi:green:batt",
"tpacpi::dock_active", "tpacpi::bay_active", "tpacpi::dock_batt",
"tpacpi::unknown_led", "tpacpi::standby", "tpacpi::dock_status1",
"tpacpi::dock_status2", "tpacpi::unknown_led2", "tpacpi::unknown_led3",
"tpacpi::thinkvantage".

Due to limitations in the sysfs LED class, if the status of the LED
indicators cannot be read due to an error, thinkpad-acpi will report it as
a brightness of zero (same as LED off).

If the thinkpad firmware doesn't support reading the current status,
trying to read the current LED brightness will just return whatever
brightness was last written to that attribute.

These LEDs can blink using hardware acceleration.  To request that a
ThinkPad indicator LED should blink in hardware accelerated mode, use the
"timer" trigger, and leave the delay_on and delay_off parameters set to
zero (to request hardware acceleration autodetection).

LEDs that are known not to exist in a given ThinkPad model are not
made available through the sysfs interface.  If you have a dock and you
notice there are LEDs listed for your ThinkPad that do not exist (and
are not in the dock), or if you notice that there are missing LEDs,
a report to ibm-acpi-devel@lists.sourceforge.net is appreciated.


ACPI sounds -- /proc/acpi/ibm/beep
----------------------------------

The BEEP method is used internally by the ACPI firmware to provide
audible alerts in various situations. This feature allows the same
sounds to be triggered manually.

The commands are non-negative integer numbers:

	echo <number> >/proc/acpi/ibm/beep

The valid <number> range is 0 to 17. Not all numbers trigger sounds
and the sounds vary from model to model. Here is the behavior on the
X40:

	0 - stop a sound in progress (but use 17 to stop 16)
	2 - two beeps, pause, third beep ("low battery")
	3 - single beep
	4 - high, followed by low-pitched beep ("unable")
	5 - single beep
	6 - very high, followed by high-pitched beep ("AC/DC")
	7 - high-pitched beep
	9 - three short beeps
	10 - very long beep
	12 - low-pitched beep
	15 - three high-pitched beeps repeating constantly, stop with 0
	16 - one medium-pitched beep repeating constantly, stop with 17
	17 - stop 16


Temperature sensors
-------------------

procfs: /proc/acpi/ibm/thermal
sysfs device attributes: (hwmon "thinkpad") temp*_input

Most ThinkPads include six or more separate temperature sensors but only
expose the CPU temperature through the standard ACPI methods.  This
feature shows readings from up to eight different sensors on older
ThinkPads, and up to sixteen different sensors on newer ThinkPads.

For example, on the X40, a typical output may be:
temperatures:   42 42 45 41 36 -128 33 -128

On the T43/p, a typical output may be:
temperatures:   48 48 36 52 38 -128 31 -128 48 52 48 -128 -128 -128 -128 -128

The mapping of thermal sensors to physical locations varies depending on
system-board model (and thus, on ThinkPad model).

http://thinkwiki.org/wiki/Thermal_Sensors is a public wiki page that
tries to track down these locations for various models.

Most (newer?) models seem to follow this pattern:

1:  CPU
2:  (depends on model)
3:  (depends on model)
4:  GPU
5:  Main battery: main sensor
6:  Bay battery: main sensor
7:  Main battery: secondary sensor
8:  Bay battery: secondary sensor
9-15: (depends on model)

For the R51 (source: Thomas Gruber):
2:  Mini-PCI
3:  Internal HDD

For the T43, T43/p (source: Shmidoax/Thinkwiki.org)
http://thinkwiki.org/wiki/Thermal_Sensors#ThinkPad_T43.2C_T43p
2:  System board, left side (near PCMCIA slot), reported as HDAPS temp
3:  PCMCIA slot
9:  MCH (northbridge) to DRAM Bus
10: Clock-generator, mini-pci card and ICH (southbridge), under Mini-PCI
    card, under touchpad
11: Power regulator, underside of system board, below F2 key

The A31 has a very atypical layout for the thermal sensors
(source: Milos Popovic, http://thinkwiki.org/wiki/Thermal_Sensors#ThinkPad_A31)
1:  CPU
2:  Main Battery: main sensor
3:  Power Converter
4:  Bay Battery: main sensor
5:  MCH (northbridge)
6:  PCMCIA/ambient
7:  Main Battery: secondary sensor
8:  Bay Battery: secondary sensor


Procfs notes:
	Readings from sensors that are not available return -128.
	No commands can be written to this file.

Sysfs notes:
	Sensors that are not available return the ENXIO error.  This
	status may change at runtime, as there are hotplug thermal
	sensors, like those inside the batteries and docks.

	thinkpad-acpi thermal sensors are reported through the hwmon
	subsystem, and follow all of the hwmon guidelines at
	Documentation/hwmon.

EXPERIMENTAL: Embedded controller register dump
-----------------------------------------------

This feature is not included in the thinkpad driver anymore.
Instead the EC can be accessed through /sys/kernel/debug/ec with
a userspace tool which can be found here:
ftp://ftp.suse.com/pub/people/trenn/sources/ec

Use it to determine the register holding the fan
speed on some models. To do that, do the following:
	- make sure the battery is fully charged
	- make sure the fan is running
	- use above mentioned tool to read out the EC

Often fan and temperature values vary between
readings. Since temperatures don't change vary fast, you can take
several quick dumps to eliminate them.

You can use a similar method to figure out the meaning of other
embedded controller registers - e.g. make sure nothing else changes
except the charging or discharging battery to determine which
registers contain the current battery capacity, etc. If you experiment
with this, do send me your results (including some complete dumps with
a description of the conditions when they were taken.)


LCD brightness control
----------------------

procfs: /proc/acpi/ibm/brightness
sysfs backlight device "thinkpad_screen"

This feature allows software control of the LCD brightness on ThinkPad
models which don't have a hardware brightness slider.

It has some limitations: the LCD backlight cannot be actually turned
on or off by this interface, it just controls the backlight brightness
level.

On IBM (and some of the earlier Lenovo) ThinkPads, the backlight control
has eight brightness levels, ranging from 0 to 7.  Some of the levels
may not be distinct.  Later Lenovo models that implement the ACPI
display backlight brightness control methods have 16 levels, ranging
from 0 to 15.

For IBM ThinkPads, there are two interfaces to the firmware for direct
brightness control, EC and UCMS (or CMOS).  To select which one should be
used, use the brightness_mode module parameter: brightness_mode=1 selects
EC mode, brightness_mode=2 selects UCMS mode, brightness_mode=3 selects EC
mode with NVRAM backing (so that brightness changes are remembered across
shutdown/reboot).

The driver tries to select which interface to use from a table of
defaults for each ThinkPad model.  If it makes a wrong choice, please
report this as a bug, so that we can fix it.

Lenovo ThinkPads only support brightness_mode=2 (UCMS).

When display backlight brightness controls are available through the
standard ACPI interface, it is best to use it instead of this direct
ThinkPad-specific interface.  The driver will disable its native
backlight brightness control interface if it detects that the standard
ACPI interface is available in the ThinkPad.

If you want to use the thinkpad-acpi backlight brightness control
instead of the generic ACPI video backlight brightness control for some
reason, you should use the acpi_backlight=vendor kernel parameter.

The brightness_enable module parameter can be used to control whether
the LCD brightness control feature will be enabled when available.
brightness_enable=0 forces it to be disabled.  brightness_enable=1
forces it to be enabled when available, even if the standard ACPI
interface is also available.

Procfs notes:

	The available commands are:

	echo up   >/proc/acpi/ibm/brightness
	echo down >/proc/acpi/ibm/brightness
	echo 'level <level>' >/proc/acpi/ibm/brightness

Sysfs notes:

The interface is implemented through the backlight sysfs class, which is
poorly documented at this time.

Locate the thinkpad_screen device under /sys/class/backlight, and inside
it there will be the following attributes:

	max_brightness:
		Reads the maximum brightness the hardware can be set to.
		The minimum is always zero.

	actual_brightness:
		Reads what brightness the screen is set to at this instant.

	brightness:
		Writes request the driver to change brightness to the
		given value.  Reads will tell you what brightness the
		driver is trying to set the display to when "power" is set
		to zero and the display has not been dimmed by a kernel
		power management event.

	power:
		power management mode, where 0 is "display on", and 1 to 3
		will dim the display backlight to brightness level 0
		because thinkpad-acpi cannot really turn the backlight
		off.  Kernel power management events can temporarily
		increase the current power management level, i.e. they can
		dim the display.


WARNING:

    Whatever you do, do NOT ever call thinkpad-acpi backlight-level change
    interface and the ACPI-based backlight level change interface
    (available on newer BIOSes, and driven by the Linux ACPI video driver)
    at the same time.  The two will interact in bad ways, do funny things,
    and maybe reduce the life of the backlight lamps by needlessly kicking
    its level up and down at every change.


Volume control (Console Audio control)
--------------------------------------

procfs: /proc/acpi/ibm/volume
ALSA: "ThinkPad Console Audio Control", default ID: "ThinkPadEC"

NOTE: by default, the volume control interface operates in read-only
mode, as it is supposed to be used for on-screen-display purposes.
The read/write mode can be enabled through the use of the
"volume_control=1" module parameter.

NOTE: distros are urged to not enable volume_control by default, this
should be done by the local admin only.  The ThinkPad UI is for the
console audio control to be done through the volume keys only, and for
the desktop environment to just provide on-screen-display feedback.
Software volume control should be done only in the main AC97/HDA
mixer.


About the ThinkPad Console Audio control:

ThinkPads have a built-in amplifier and muting circuit that drives the
console headphone and speakers.  This circuit is after the main AC97
or HDA mixer in the audio path, and under exclusive control of the
firmware.

ThinkPads have three special hotkeys to interact with the console
audio control: volume up, volume down and mute.

It is worth noting that the normal way the mute function works (on
ThinkPads that do not have a "mute LED") is:

1. Press mute to mute.  It will *always* mute, you can press it as
   many times as you want, and the sound will remain mute.

2. Press either volume key to unmute the ThinkPad (it will _not_
   change the volume, it will just unmute).

This is a very superior design when compared to the cheap software-only
mute-toggle solution found on normal consumer laptops:  you can be
absolutely sure the ThinkPad will not make noise if you press the mute
button, no matter the previous state.

The IBM ThinkPads, and the earlier Lenovo ThinkPads have variable-gain
amplifiers driving the speakers and headphone output, and the firmware
also handles volume control for the headphone and speakers on these
ThinkPads without any help from the operating system (this volume
control stage exists after the main AC97 or HDA mixer in the audio
path).

The newer Lenovo models only have firmware mute control, and depend on
the main HDA mixer to do volume control (which is done by the operating
system).  In this case, the volume keys are filtered out for unmute
key press (there are some firmware bugs in this area) and delivered as
normal key presses to the operating system (thinkpad-acpi is not
involved).


The ThinkPad-ACPI volume control:

The preferred way to interact with the Console Audio control is the
ALSA interface.

The legacy procfs interface allows one to read the current state,
and if volume control is enabled, accepts the following commands:

	echo up   >/proc/acpi/ibm/volume
	echo down >/proc/acpi/ibm/volume
	echo mute >/proc/acpi/ibm/volume
	echo unmute >/proc/acpi/ibm/volume
	echo 'level <level>' >/proc/acpi/ibm/volume

The <level> number range is 0 to 14 although not all of them may be
distinct. To unmute the volume after the mute command, use either the
up or down command (the level command will not unmute the volume), or
the unmute command.

You can use the volume_capabilities parameter to tell the driver
whether your thinkpad has volume control or mute-only control:
volume_capabilities=1 for mixers with mute and volume control,
volume_capabilities=2 for mixers with only mute control.

If the driver misdetects the capabilities for your ThinkPad model,
please report this to ibm-acpi-devel@lists.sourceforge.net, so that we
can update the driver.

There are two strategies for volume control.  To select which one
should be used, use the volume_mode module parameter: volume_mode=1
selects EC mode, and volume_mode=3 selects EC mode with NVRAM backing
(so that volume/mute changes are remembered across shutdown/reboot).

The driver will operate in volume_mode=3 by default. If that does not
work well on your ThinkPad model, please report this to
ibm-acpi-devel@lists.sourceforge.net.

The driver supports the standard ALSA module parameters.  If the ALSA
mixer is disabled, the driver will disable all volume functionality.


Fan control and monitoring: fan speed, fan enable/disable
---------------------------------------------------------

procfs: /proc/acpi/ibm/fan
sysfs device attributes: (hwmon "thinkpad") fan1_input, pwm1,
			  pwm1_enable, fan2_input
sysfs hwmon driver attributes: fan_watchdog

NOTE NOTE NOTE: fan control operations are disabled by default for
safety reasons.  To enable them, the module parameter "fan_control=1"
must be given to thinkpad-acpi.

This feature attempts to show the current fan speed, control mode and
other fan data that might be available.  The speed is read directly
from the hardware registers of the embedded controller.  This is known
to work on later R, T, X and Z series ThinkPads but may show a bogus
value on other models.

Some Lenovo ThinkPads support a secondary fan.  This fan cannot be
controlled separately, it shares the main fan control.

Fan levels:

Most ThinkPad fans work in "levels" at the firmware interface.  Level 0
stops the fan.  The higher the level, the higher the fan speed, although
adjacent levels often map to the same fan speed.  7 is the highest
level, where the fan reaches the maximum recommended speed.

Level "auto" means the EC changes the fan level according to some
internal algorithm, usually based on readings from the thermal sensors.

There is also a "full-speed" level, also known as "disengaged" level.
In this level, the EC disables the speed-locked closed-loop fan control,
and drives the fan as fast as it can go, which might exceed hardware
limits, so use this level with caution.

The fan usually ramps up or down slowly from one speed to another, and
it is normal for the EC to take several seconds to react to fan
commands.  The full-speed level may take up to two minutes to ramp up to
maximum speed, and in some ThinkPads, the tachometer readings go stale
while the EC is transitioning to the full-speed level.

WARNING WARNING WARNING: do not leave the fan disabled unless you are
monitoring all of the temperature sensor readings and you are ready to
enable it if necessary to avoid overheating.

An enabled fan in level "auto" may stop spinning if the EC decides the
ThinkPad is cool enough and doesn't need the extra airflow.  This is
normal, and the EC will spin the fan up if the various thermal readings
rise too much.

On the X40, this seems to depend on the CPU and HDD temperatures.
Specifically, the fan is turned on when either the CPU temperature
climbs to 56 degrees or the HDD temperature climbs to 46 degrees.  The
fan is turned off when the CPU temperature drops to 49 degrees and the
HDD temperature drops to 41 degrees.  These thresholds cannot
currently be controlled.

The ThinkPad's ACPI DSDT code will reprogram the fan on its own when
certain conditions are met.  It will override any fan programming done
through thinkpad-acpi.

The thinkpad-acpi kernel driver can be programmed to revert the fan
level to a safe setting if userspace does not issue one of the procfs
fan commands: "enable", "disable", "level" or "watchdog", or if there
are no writes to pwm1_enable (or to pwm1 *if and only if* pwm1_enable is
set to 1, manual mode) within a configurable amount of time of up to
120 seconds.  This functionality is called fan safety watchdog.

Note that the watchdog timer stops after it enables the fan.  It will be
rearmed again automatically (using the same interval) when one of the
above mentioned fan commands is received.  The fan watchdog is,
therefore, not suitable to protect against fan mode changes made through
means other than the "enable", "disable", and "level" procfs fan
commands, or the hwmon fan control sysfs interface.

Procfs notes:

The fan may be enabled or disabled with the following commands:

	echo enable  >/proc/acpi/ibm/fan
	echo disable >/proc/acpi/ibm/fan

Placing a fan on level 0 is the same as disabling it.  Enabling a fan
will try to place it in a safe level if it is too slow or disabled.

The fan level can be controlled with the command:

	echo 'level <level>' > /proc/acpi/ibm/fan

Where <level> is an integer from 0 to 7, or one of the words "auto" or
"full-speed" (without the quotes).  Not all ThinkPads support the "auto"
and "full-speed" levels.  The driver accepts "disengaged" as an alias for
"full-speed", and reports it as "disengaged" for backwards
compatibility.

On the X31 and X40 (and ONLY on those models), the fan speed can be
controlled to a certain degree.  Once the fan is running, it can be
forced to run faster or slower with the following command:

	echo 'speed <speed>' > /proc/acpi/ibm/fan

The sustainable range of fan speeds on the X40 appears to be from about
3700 to about 7350. Values outside this range either do not have any
effect or the fan speed eventually settles somewhere in that range.  The
fan cannot be stopped or started with this command.  This functionality
is incomplete, and not available through the sysfs interface.

To program the safety watchdog, use the "watchdog" command.

	echo 'watchdog <interval in seconds>' > /proc/acpi/ibm/fan

If you want to disable the watchdog, use 0 as the interval.

Sysfs notes:

The sysfs interface follows the hwmon subsystem guidelines for the most
part, and the exception is the fan safety watchdog.

Writes to any of the sysfs attributes may return the EINVAL error if
that operation is not supported in a given ThinkPad or if the parameter
is out-of-bounds, and EPERM if it is forbidden.  They may also return
EINTR (interrupted system call), and EIO (I/O error while trying to talk
to the firmware).

Features not yet implemented by the driver return ENOSYS.

hwmon device attribute pwm1_enable:
	0: PWM offline (fan is set to full-speed mode)
	1: Manual PWM control (use pwm1 to set fan level)
	2: Hardware PWM control (EC "auto" mode)
	3: reserved (Software PWM control, not implemented yet)

	Modes 0 and 2 are not supported by all ThinkPads, and the
	driver is not always able to detect this.  If it does know a
	mode is unsupported, it will return -EINVAL.

hwmon device attribute pwm1:
	Fan level, scaled from the firmware values of 0-7 to the hwmon
	scale of 0-255.  0 means fan stopped, 255 means highest normal
	speed (level 7).

	This attribute only commands the fan if pmw1_enable is set to 1
	(manual PWM control).

hwmon device attribute fan1_input:
	Fan tachometer reading, in RPM.  May go stale on certain
	ThinkPads while the EC transitions the PWM to offline mode,
	which can take up to two minutes.  May return rubbish on older
	ThinkPads.

hwmon device attribute fan2_input:
	Fan tachometer reading, in RPM, for the secondary fan.
	Available only on some ThinkPads.  If the secondary fan is
	not installed, will always read 0.

hwmon driver attribute fan_watchdog:
	Fan safety watchdog timer interval, in seconds.  Minimum is
	1 second, maximum is 120 seconds.  0 disables the watchdog.

To stop the fan: set pwm1 to zero, and pwm1_enable to 1.

To start the fan in a safe mode: set pwm1_enable to 2.  If that fails
with EINVAL, try to set pwm1_enable to 1 and pwm1 to at least 128 (255
would be the safest choice, though).


WAN
---

procfs: /proc/acpi/ibm/wan
sysfs device attribute: wwan_enable (deprecated)
sysfs rfkill class: switch "tpacpi_wwan_sw"

This feature shows the presence and current state of the built-in
Wireless WAN device.

If the ThinkPad supports it, the WWAN state is stored in NVRAM,
so it is kept across reboots and power-off.

It was tested on a Lenovo ThinkPad X60. It should probably work on other
ThinkPad models which come with this module installed.

Procfs notes:

If the W-WAN card is installed, the following commands can be used:

	echo enable > /proc/acpi/ibm/wan
	echo disable > /proc/acpi/ibm/wan

Sysfs notes:

	If the W-WAN card is installed, it can be enabled /
	disabled through the "wwan_enable" thinkpad-acpi device
	attribute, and its current status can also be queried.

	enable:
		0: disables WWAN card / WWAN card is disabled
		1: enables WWAN card / WWAN card is enabled.

	Note: this interface has been superseded by the	generic rfkill
	class.  It has been deprecated, and it will be removed in year
	2010.

	rfkill controller switch "tpacpi_wwan_sw": refer to
	Documentation/rfkill.txt for details.


EXPERIMENTAL: UWB
-----------------

This feature is considered EXPERIMENTAL because it has not been extensively
tested and validated in various ThinkPad models yet.  The feature may not
work as expected. USE WITH CAUTION! To use this feature, you need to supply
the experimental=1 parameter when loading the module.

sysfs rfkill class: switch "tpacpi_uwb_sw"

This feature exports an rfkill controller for the UWB device, if one is
present and enabled in the BIOS.

Sysfs notes:

	rfkill controller switch "tpacpi_uwb_sw": refer to
	Documentation/rfkill.txt for details.


Multiple Commands, Module Parameters
------------------------------------

Multiple commands can be written to the proc files in one shot by
separating them with commas, for example:

	echo enable,0xffff > /proc/acpi/ibm/hotkey
	echo lcd_disable,crt_enable > /proc/acpi/ibm/video

Commands can also be specified when loading the thinkpad-acpi module,
for example:

	modprobe thinkpad_acpi hotkey=enable,0xffff video=auto_disable


Enabling debugging output
-------------------------

The module takes a debug parameter which can be used to selectively
enable various classes of debugging output, for example:

	 modprobe thinkpad_acpi debug=0xffff

will enable all debugging output classes.  It takes a bitmask, so
to enable more than one output class, just add their values.

	Debug bitmask		Description
	0x8000			Disclose PID of userspace programs
				accessing some functions of the driver
	0x0001			Initialization and probing
	0x0002			Removal
	0x0004			RF Transmitter control (RFKILL)
				(bluetooth, WWAN, UWB...)
	0x0008			HKEY event interface, hotkeys
	0x0010			Fan control
	0x0020			Backlight brightness
	0x0040			Audio mixer/volume control

There is also a kernel build option to enable more debugging
information, which may be necessary to debug driver problems.

The level of debugging information output by the driver can be changed
at runtime through sysfs, using the driver attribute debug_level.  The
attribute takes the same bitmask as the debug module parameter above.


Force loading of module
-----------------------

If thinkpad-acpi refuses to detect your ThinkPad, you can try to specify
the module parameter force_load=1.  Regardless of whether this works or
not, please contact ibm-acpi-devel@lists.sourceforge.net with a report.


Sysfs interface changelog:

0x000100:	Initial sysfs support, as a single platform driver and
		device.
0x000200:	Hot key support for 32 hot keys, and radio slider switch
		support.
0x010000:	Hot keys are now handled by default over the input
		layer, the radio switch generates input event EV_RADIO,
		and the driver enables hot key handling by default in
		the firmware.

0x020000:	ABI fix: added a separate hwmon platform device and
		driver, which must be located by name (thinkpad)
		and the hwmon class for libsensors4 (lm-sensors 3)
		compatibility.  Moved all hwmon attributes to this
		new platform device.

0x020100:	Marker for thinkpad-acpi with hot key NVRAM polling
		support.  If you must, use it to know you should not
		start a userspace NVRAM poller (allows to detect when
		NVRAM is compiled out by the user because it is
		unneeded/undesired in the first place).
0x020101:	Marker for thinkpad-acpi with hot key NVRAM polling
		and proper hotkey_mask semantics (version 8 of the
		NVRAM polling patch).  Some development snapshots of
		0.18 had an earlier version that did strange things
		to hotkey_mask.

0x020200:	Add poll()/select() support to the following attributes:
		hotkey_radio_sw, wakeup_hotunplug_complete, wakeup_reason

0x020300:	hotkey enable/disable support removed, attributes
		hotkey_bios_enabled and hotkey_enable deprecated and
		marked for removal.

0x020400:	Marker for 16 LEDs support.  Also, LEDs that are known
		to not exist in a given model are not registered with
		the LED sysfs class anymore.

0x020500:	Updated hotkey driver, hotkey_mask is always available
		and it is always able to disable hot keys.  Very old
		thinkpads are properly supported.  hotkey_bios_mask
		is deprecated and marked for removal.

0x020600:	Marker for backlight change event support.

0x020700:	Support for mute-only mixers.
		Volume control in read-only mode by default.
		Marker for ALSA mixer support.