Documentation/input/event-codes.txt - kernel/common - Git at Google

 The input protocol uses a map of types and codes to express input device values
 to userspace. This document describes the types and codes and how and when they
 may be used.

 A single hardware event generates multiple input events. Each input event
 contains the new value of a single data item. A special event type, EV_SYN, is
 used to separate input events into packets of input data changes occurring at
 the same moment in time. In the following, the term "event" refers to a single
 input event encompassing a type, code, and value.

 The input protocol is a stateful protocol. Events are emitted only when values
 of event codes have changed. However, the state is maintained within the Linux
 input subsystem; drivers do not need to maintain the state and may attempt to
 emit unchanged values without harm. Userspace may obtain the current state of
 event code values using the EVIOCG* ioctls defined in linux/input.h. The event
 reports supported by a device are also provided by sysfs in
 class/input/event*/device/capabilities/, and the properties of a device are
 provided in class/input/event*/device/properties.

 Event types:
 ===========
 Event types are groupings of codes under a logical input construct. Each
 type has a set of applicable codes to be used in generating events. See the
 Codes section for details on valid codes for each type.

 * EV_SYN:
   - Used as markers to separate events. Events may be separated in time or in
     space, such as with the multitouch protocol.

 * EV_KEY:
   - Used to describe state changes of keyboards, buttons, or other key-like
     devices.

 * EV_REL:
   - Used to describe relative axis value changes, e.g. moving the mouse 5 units
     to the left.

 * EV_ABS:
   - Used to describe absolute axis value changes, e.g. describing the
     coordinates of a touch on a touchscreen.

 * EV_MSC:
   - Used to describe miscellaneous input data that do not fit into other types.

 * EV_SW:
   - Used to describe binary state input switches.

 * EV_LED:
   - Used to turn LEDs on devices on and off.

 * EV_SND:
   - Used to output sound to devices.

 * EV_REP:
   - Used for autorepeating devices.

 * EV_FF:
   - Used to send force feedback commands to an input device.

 * EV_PWR:
   - A special type for power button and switch input.

 * EV_FF_STATUS:
   - Used to receive force feedback device status.

 Event codes:
 ===========
 Event codes define the precise type of event.

 EV_SYN:
 ----------
 EV_SYN event values are undefined. Their usage is defined only by when they are
 sent in the evdev event stream.

 * SYN_REPORT:
   - Used to synchronize and separate events into packets of input data changes
     occurring at the same moment in time. For example, motion of a mouse may set
     the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
     motion will emit more REL_X and REL_Y values and send another SYN_REPORT.

 * SYN_CONFIG:
   - TBD

 * SYN_MT_REPORT:
   - Used to synchronize and separate touch events. See the
     multi-touch-protocol.txt document for more information.

 * SYN_DROPPED:
   - Used to indicate buffer overrun in the evdev client's event queue.
     Client should ignore all events up to and including next SYN_REPORT
     event and query the device (using EVIOCG* ioctls) to obtain its
     current state.

 EV_KEY:
 ----------
 EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
 to represent the 'A' key on a keyboard. When a key is depressed, an event with
 the key's code is emitted with value 1. When the key is released, an event is
 emitted with value 0. Some hardware send events when a key is repeated. These
 events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
 BTN_<name> is used for other types of momentary switch events.

 A few EV_KEY codes have special meanings:

 * BTN_TOOL_<name>:
   - These codes are used in conjunction with input trackpads, tablets, and
     touchscreens. These devices may be used with fingers, pens, or other tools.
     When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
     code should be set to a value of 1. When the tool is no longer interacting
     with the input device, the BTN_TOOL_<name> code should be reset to 0. All
     trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
     code when events are generated.

 * BTN_TOUCH:
     BTN_TOUCH is used for touch contact. While an input tool is determined to be
     within meaningful physical contact, the value of this property must be set
     to 1. Meaningful physical contact may mean any contact, or it may mean
     contact conditioned by an implementation defined property. For example, a
     touchpad may set the value to 1 only when the touch pressure rises above a
     certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
     example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
     pen is hovering over but not touching the tablet surface.

 Note: For appropriate function of the legacy mousedev emulation driver,
 BTN_TOUCH must be the first evdev code emitted in a synchronization frame.

 Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
 interpreted as a touchpad by userspace, while a similar device without
 BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
 with current userspace it is recommended to follow this distinction. In the
 future, this distinction will be deprecated and the device properties ioctl
 EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.

 * BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
   - These codes denote one, two, three, and four finger interaction on a
     trackpad or touchscreen. For example, if the user uses two fingers and moves
     them on the touchpad in an effort to scroll content on screen,
     BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
     Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
     purpose. A trackpad event generated by finger touches should generate events
     for one code from each group. At most only one of these BTN_TOOL_<name>
     codes should have a value of 1 during any synchronization frame.

 Note: Historically some drivers emitted multiple of the finger count codes with
 a value of 1 in the same synchronization frame. This usage is deprecated.

 Note: In multitouch drivers, the input_mt_report_finger_count() function should
 be used to emit these codes. Please see multi-touch-protocol.txt for details.

 EV_REL:
 ----------
 EV_REL events describe relative changes in a property. For example, a mouse may
 move to the left by a certain number of units, but its absolute position in
 space is unknown. If the absolute position is known, EV_ABS codes should be used
 instead of EV_REL codes.

 A few EV_REL codes have special meanings:

 * REL_WHEEL, REL_HWHEEL:
   - These codes are used for vertical and horizontal scroll wheels,
     respectively.

 EV_ABS:
 ----------
 EV_ABS events describe absolute changes in a property. For example, a touchpad
 may emit coordinates for a touch location.

 A few EV_ABS codes have special meanings:

 * ABS_DISTANCE:
   - Used to describe the distance of a tool from an interaction surface. This
     event should only be emitted while the tool is hovering, meaning in close
     proximity of the device and while the value of the BTN_TOUCH code is 0. If
     the input device may be used freely in three dimensions, consider ABS_Z
     instead.
   - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
     proximity and set to 0 when the tool leaves detectable proximity.
     BTN_TOOL_<name> signals the type of tool that is currently detected by the
     hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.

 * ABS_MT_<name>:
   - Used to describe multitouch input events. Please see
     multi-touch-protocol.txt for details.

 EV_SW:
 ----------
 EV_SW events describe stateful binary switches. For example, the SW_LID code is
 used to denote when a laptop lid is closed.

 Upon binding to a device or resuming from suspend, a driver must report
 the current switch state. This ensures that the device, kernel, and userspace
 state is in sync.

 Upon resume, if the switch state is the same as before suspend, then the input
 subsystem will filter out the duplicate switch state reports. The driver does
 not need to keep the state of the switch at any time.

 EV_MSC:
 ----------
 EV_MSC events are used for input and output events that do not fall under other
 categories.

 A few EV_MSC codes have special meaning:

 * MSC_TIMESTAMP:
   - Used to report the number of microseconds since the last reset. This event
     should be coded as an uint32 value, which is allowed to wrap around with
     no special consequence. It is assumed that the time difference between two
     consecutive events is reliable on a reasonable time scale (hours).
     A reset to zero can happen, in which case the time since the last event is
     unknown.  If the device does not provide this information, the driver must
     not provide it to user space.

 EV_LED:
 ----------
 EV_LED events are used for input and output to set and query the state of
 various LEDs on devices.

 EV_REP:
 ----------
 EV_REP events are used for specifying autorepeating events.

 EV_SND:
 ----------
 EV_SND events are used for sending sound commands to simple sound output
 devices.

 EV_FF:
 ----------
 EV_FF events are used to initialize a force feedback capable device and to cause
 such device to feedback.

 EV_PWR:
 ----------
 EV_PWR events are a special type of event used specifically for power
 management. Its usage is not well defined. To be addressed later.

 Device properties:
 =================
 Normally, userspace sets up an input device based on the data it emits,
 i.e., the event types. In the case of two devices emitting the same event
 types, additional information can be provided in the form of device
 properties.

 INPUT_PROP_DIRECT + INPUT_PROP_POINTER:
 --------------------------------------
 The INPUT_PROP_DIRECT property indicates that device coordinates should be
 directly mapped to screen coordinates (not taking into account trivial
 transformations, such as scaling, flipping and rotating). Non-direct input
 devices require non-trivial transformation, such as absolute to relative
 transformation for touchpads. Typical direct input devices: touchscreens,
 drawing tablets; non-direct devices: touchpads, mice.

 The INPUT_PROP_POINTER property indicates that the device is not transposed
 on the screen and thus requires use of an on-screen pointer to trace user's
 movements.  Typical pointer devices: touchpads, tablets, mice; non-pointer
 device: touchscreen.

 If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
 considered undefined and the device type should be deduced in the
 traditional way, using emitted event types.

 INPUT_PROP_BUTTONPAD:
 --------------------
 For touchpads where the button is placed beneath the surface, such that
 pressing down on the pad causes a button click, this property should be
 set. Common in clickpad notebooks and macbooks from 2009 and onwards.

 Originally, the buttonpad property was coded into the bcm5974 driver
 version field under the name integrated button. For backwards
 compatibility, both methods need to be checked in userspace.

 INPUT_PROP_SEMI_MT:
 ------------------
 Some touchpads, most common between 2008 and 2011, can detect the presence
 of multiple contacts without resolving the individual positions; only the
 number of contacts and a rectangular shape is known. For such
 touchpads, the semi-mt property should be set.

 Depending on the device, the rectangle may enclose all touches, like a
 bounding box, or just some of them, for instance the two most recent
 touches. The diversity makes the rectangle of limited use, but some
 gestures can normally be extracted from it.

 If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
 device.

 INPUT_PROP_TOPBUTTONPAD:
 -----------------------
 Some laptops, most notably the Lenovo *40 series provide a trackstick
 device but do not have physical buttons associated with the trackstick
 device. Instead, the top area of the touchpad is marked to show
 visual/haptic areas for left, middle, right buttons intended to be used
 with the trackstick.

 If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
 accordingly. This property does not affect kernel behavior.
 The kernel does not provide button emulation for such devices but treats
 them as any other INPUT_PROP_BUTTONPAD device.

 INPUT_PROP_ACCELEROMETER
 -------------------------
 Directional axes on this device (absolute and/or relative x, y, z) represent
 accelerometer data. All other axes retain their meaning. A device must not mix
 regular directional axes and accelerometer axes on the same event node.

 Guidelines:
 ==========
 The guidelines below ensure proper single-touch and multi-finger functionality.
 For multi-touch functionality, see the multi-touch-protocol.txt document for
 more information.

 Mice:
 ----------
 REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
 the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
 further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
 scroll wheel events where available.

 Touchscreens:
 ----------
 ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
 used to report when a touch is active on the screen.
 BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
 contact. BTN_TOOL_<name> events should be reported where possible.

 For new hardware, INPUT_PROP_DIRECT should be set.

 Trackpads:
 ----------
 Legacy trackpads that only provide relative position information must report
 events like mice described above.

 Trackpads that provide absolute touch position must report ABS_{X,Y} for the
 location of the touch. BTN_TOUCH should be used to report when a touch is active
 on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
 be used to report the number of touches active on the trackpad.

 For new hardware, INPUT_PROP_POINTER should be set.

 Tablets:
 ----------
 BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
 the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
 should be used to report when the tool is in contact with the tablet.
 BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
 button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
 BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
 meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
 purpose on the device.

 For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
	The input protocol uses a map of types and codes to express input device values
	to userspace. This document describes the types and codes and how and when they
	may be used.

	A single hardware event generates multiple input events. Each input event
	contains the new value of a single data item. A special event type, EV_SYN, is
	used to separate input events into packets of input data changes occurring at
	the same moment in time. In the following, the term "event" refers to a single
	input event encompassing a type, code, and value.

	The input protocol is a stateful protocol. Events are emitted only when values
	of event codes have changed. However, the state is maintained within the Linux
	input subsystem; drivers do not need to maintain the state and may attempt to
	emit unchanged values without harm. Userspace may obtain the current state of
	event code values using the EVIOCG* ioctls defined in linux/input.h. The event
	reports supported by a device are also provided by sysfs in
	class/input/event*/device/capabilities/, and the properties of a device are
	provided in class/input/event*/device/properties.

	Event types:
	===========
	Event types are groupings of codes under a logical input construct. Each
	type has a set of applicable codes to be used in generating events. See the
	Codes section for details on valid codes for each type.

	* EV_SYN:
	- Used as markers to separate events. Events may be separated in time or in
	space, such as with the multitouch protocol.

	* EV_KEY:
	- Used to describe state changes of keyboards, buttons, or other key-like
	devices.

	* EV_REL:
	- Used to describe relative axis value changes, e.g. moving the mouse 5 units
	to the left.

	* EV_ABS:
	- Used to describe absolute axis value changes, e.g. describing the
	coordinates of a touch on a touchscreen.

	* EV_MSC:
	- Used to describe miscellaneous input data that do not fit into other types.

	* EV_SW:
	- Used to describe binary state input switches.

	* EV_LED:
	- Used to turn LEDs on devices on and off.

	* EV_SND:
	- Used to output sound to devices.

	* EV_REP:
	- Used for autorepeating devices.

	* EV_FF:
	- Used to send force feedback commands to an input device.

	* EV_PWR:
	- A special type for power button and switch input.

	* EV_FF_STATUS:
	- Used to receive force feedback device status.

	Event codes:
	===========
	Event codes define the precise type of event.

	EV_SYN:
	----------
	EV_SYN event values are undefined. Their usage is defined only by when they are
	sent in the evdev event stream.

	* SYN_REPORT:
	- Used to synchronize and separate events into packets of input data changes
	occurring at the same moment in time. For example, motion of a mouse may set
	the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
	motion will emit more REL_X and REL_Y values and send another SYN_REPORT.

	* SYN_CONFIG:
	- TBD

	* SYN_MT_REPORT:
	- Used to synchronize and separate touch events. See the
	multi-touch-protocol.txt document for more information.

	* SYN_DROPPED:
	- Used to indicate buffer overrun in the evdev client's event queue.
	Client should ignore all events up to and including next SYN_REPORT
	event and query the device (using EVIOCG* ioctls) to obtain its
	current state.

	EV_KEY:
	----------
	EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
	to represent the 'A' key on a keyboard. When a key is depressed, an event with
	the key's code is emitted with value 1. When the key is released, an event is
	emitted with value 0. Some hardware send events when a key is repeated. These
	events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
	BTN_<name> is used for other types of momentary switch events.

	A few EV_KEY codes have special meanings:

	* BTN_TOOL_<name>:
	- These codes are used in conjunction with input trackpads, tablets, and
	touchscreens. These devices may be used with fingers, pens, or other tools.
	When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
	code should be set to a value of 1. When the tool is no longer interacting
	with the input device, the BTN_TOOL_<name> code should be reset to 0. All
	trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
	code when events are generated.

	* BTN_TOUCH:
	BTN_TOUCH is used for touch contact. While an input tool is determined to be
	within meaningful physical contact, the value of this property must be set
	to 1. Meaningful physical contact may mean any contact, or it may mean
	contact conditioned by an implementation defined property. For example, a
	touchpad may set the value to 1 only when the touch pressure rises above a
	certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
	example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
	pen is hovering over but not touching the tablet surface.

	Note: For appropriate function of the legacy mousedev emulation driver,
	BTN_TOUCH must be the first evdev code emitted in a synchronization frame.

	Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
	interpreted as a touchpad by userspace, while a similar device without
	BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
	with current userspace it is recommended to follow this distinction. In the
	future, this distinction will be deprecated and the device properties ioctl
	EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.

	* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
	- These codes denote one, two, three, and four finger interaction on a
	trackpad or touchscreen. For example, if the user uses two fingers and moves
	them on the touchpad in an effort to scroll content on screen,
	BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
	Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
	purpose. A trackpad event generated by finger touches should generate events
	for one code from each group. At most only one of these BTN_TOOL_<name>
	codes should have a value of 1 during any synchronization frame.

	Note: Historically some drivers emitted multiple of the finger count codes with
	a value of 1 in the same synchronization frame. This usage is deprecated.

	Note: In multitouch drivers, the input_mt_report_finger_count() function should
	be used to emit these codes. Please see multi-touch-protocol.txt for details.

	EV_REL:
	----------
	EV_REL events describe relative changes in a property. For example, a mouse may
	move to the left by a certain number of units, but its absolute position in
	space is unknown. If the absolute position is known, EV_ABS codes should be used
	instead of EV_REL codes.

	A few EV_REL codes have special meanings:

	* REL_WHEEL, REL_HWHEEL:
	- These codes are used for vertical and horizontal scroll wheels,
	respectively.

	EV_ABS:
	----------
	EV_ABS events describe absolute changes in a property. For example, a touchpad
	may emit coordinates for a touch location.

	A few EV_ABS codes have special meanings:

	* ABS_DISTANCE:
	- Used to describe the distance of a tool from an interaction surface. This
	event should only be emitted while the tool is hovering, meaning in close
	proximity of the device and while the value of the BTN_TOUCH code is 0. If
	the input device may be used freely in three dimensions, consider ABS_Z
	instead.
	- BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
	proximity and set to 0 when the tool leaves detectable proximity.
	BTN_TOOL_<name> signals the type of tool that is currently detected by the
	hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.

	* ABS_MT_<name>:
	- Used to describe multitouch input events. Please see
	multi-touch-protocol.txt for details.

	EV_SW:
	----------
	EV_SW events describe stateful binary switches. For example, the SW_LID code is
	used to denote when a laptop lid is closed.

	Upon binding to a device or resuming from suspend, a driver must report
	the current switch state. This ensures that the device, kernel, and userspace
	state is in sync.

	Upon resume, if the switch state is the same as before suspend, then the input
	subsystem will filter out the duplicate switch state reports. The driver does
	not need to keep the state of the switch at any time.

	EV_MSC:
	----------
	EV_MSC events are used for input and output events that do not fall under other
	categories.

	A few EV_MSC codes have special meaning:

	* MSC_TIMESTAMP:
	- Used to report the number of microseconds since the last reset. This event
	should be coded as an uint32 value, which is allowed to wrap around with
	no special consequence. It is assumed that the time difference between two
	consecutive events is reliable on a reasonable time scale (hours).
	A reset to zero can happen, in which case the time since the last event is
	unknown. If the device does not provide this information, the driver must
	not provide it to user space.

	EV_LED:
	----------
	EV_LED events are used for input and output to set and query the state of
	various LEDs on devices.

	EV_REP:
	----------
	EV_REP events are used for specifying autorepeating events.

	EV_SND:
	----------
	EV_SND events are used for sending sound commands to simple sound output
	devices.

	EV_FF:
	----------
	EV_FF events are used to initialize a force feedback capable device and to cause
	such device to feedback.

	EV_PWR:
	----------
	EV_PWR events are a special type of event used specifically for power
	management. Its usage is not well defined. To be addressed later.

	Device properties:
	=================
	Normally, userspace sets up an input device based on the data it emits,
	i.e., the event types. In the case of two devices emitting the same event
	types, additional information can be provided in the form of device
	properties.

	INPUT_PROP_DIRECT + INPUT_PROP_POINTER:
	--------------------------------------
	The INPUT_PROP_DIRECT property indicates that device coordinates should be
	directly mapped to screen coordinates (not taking into account trivial
	transformations, such as scaling, flipping and rotating). Non-direct input
	devices require non-trivial transformation, such as absolute to relative
	transformation for touchpads. Typical direct input devices: touchscreens,
	drawing tablets; non-direct devices: touchpads, mice.

	The INPUT_PROP_POINTER property indicates that the device is not transposed
	on the screen and thus requires use of an on-screen pointer to trace user's
	movements. Typical pointer devices: touchpads, tablets, mice; non-pointer
	device: touchscreen.

	If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
	considered undefined and the device type should be deduced in the
	traditional way, using emitted event types.

	INPUT_PROP_BUTTONPAD:
	--------------------
	For touchpads where the button is placed beneath the surface, such that
	pressing down on the pad causes a button click, this property should be
	set. Common in clickpad notebooks and macbooks from 2009 and onwards.

	Originally, the buttonpad property was coded into the bcm5974 driver
	version field under the name integrated button. For backwards
	compatibility, both methods need to be checked in userspace.

	INPUT_PROP_SEMI_MT:
	------------------
	Some touchpads, most common between 2008 and 2011, can detect the presence
	of multiple contacts without resolving the individual positions; only the
	number of contacts and a rectangular shape is known. For such
	touchpads, the semi-mt property should be set.

	Depending on the device, the rectangle may enclose all touches, like a
	bounding box, or just some of them, for instance the two most recent
	touches. The diversity makes the rectangle of limited use, but some
	gestures can normally be extracted from it.

	If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
	device.

	INPUT_PROP_TOPBUTTONPAD:
	-----------------------
	Some laptops, most notably the Lenovo *40 series provide a trackstick
	device but do not have physical buttons associated with the trackstick
	device. Instead, the top area of the touchpad is marked to show
	visual/haptic areas for left, middle, right buttons intended to be used
	with the trackstick.

	If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
	accordingly. This property does not affect kernel behavior.
	The kernel does not provide button emulation for such devices but treats
	them as any other INPUT_PROP_BUTTONPAD device.

	INPUT_PROP_ACCELEROMETER
	-------------------------
	Directional axes on this device (absolute and/or relative x, y, z) represent
	accelerometer data. All other axes retain their meaning. A device must not mix
	regular directional axes and accelerometer axes on the same event node.

	Guidelines:
	==========
	The guidelines below ensure proper single-touch and multi-finger functionality.
	For multi-touch functionality, see the multi-touch-protocol.txt document for
	more information.

	Mice:
	----------
	REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
	the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
	further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
	scroll wheel events where available.

	Touchscreens:
	----------
	ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
	used to report when a touch is active on the screen.
	BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
	contact. BTN_TOOL_<name> events should be reported where possible.

	For new hardware, INPUT_PROP_DIRECT should be set.

	Trackpads:
	----------
	Legacy trackpads that only provide relative position information must report
	events like mice described above.

	Trackpads that provide absolute touch position must report ABS_{X,Y} for the
	location of the touch. BTN_TOUCH should be used to report when a touch is active
	on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
	be used to report the number of touches active on the trackpad.

	For new hardware, INPUT_PROP_POINTER should be set.

	Tablets:
	----------
	BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
	the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
	should be used to report when the tool is in contact with the tablet.
	BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
	button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
	BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
	meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
	purpose on the device.

	For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.