Date:	Fri, 7 Jan 2011 19:15:56 -0600
From:	Chris Bagwell <chris@...bagwell.com>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	Nikolai Kondrashov <spbnick@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Documentation: Add evdev type and code definitions

Hi Chase,

On Fri, Jan 7, 2011 at 3:28 PM, Chase Douglas
<chase.douglas@...onical.com> wrote:
> This commit adds the file Documentation/input/evdev-codes.txt.
>
> Cc: Henrik Rydberg <rydberg@...omail.se>
> Cc: Chris Bagwell <chris@...bagwell.com>
> Cc: Peter Hutterer <peter.hutterer@...-t.net>
> Cc: Nikolai Kondrashov <spbnick@...il.com>
> Cc: linux-input@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Chase Douglas <chase.douglas@...onical.com>
> ---
>  Documentation/input/evdev-codes.txt |  206 +++++++++++++++++++++++++++++++++++
>  1 files changed, 206 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/input/evdev-codes.txt
>
> diff --git a/Documentation/input/evdev-codes.txt b/Documentation/input/evdev-codes.txt
> new file mode 100644
> index 0000000..8d7262c
> --- /dev/null
> +++ b/Documentation/input/evdev-codes.txt
> @@ -0,0 +1,206 @@
> +The evdev 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.
> +
> +The evdev protocol is a stateful protocol. Events are emitted only when values
> +of evdev 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
> +evdev code values using the EVIOCGABS ioctl defined in linux/input.h.
> +
> +Types:
> +==========
> +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 keyboard and other key-like input events.
> +
> +* EV_REL:
> +  - Used to describe relative input events, e.g. moving the mouse 5 units to the
> +    left.
> +
> +* EV_ABS:
> +  - Used to describe absolute input events, e.g. describing the coordinates of a
> +    touch on a touchscreen.
> +
> +* EV_MSC:
> +  - Used to describe miscellaneous input events 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.
> +
> +Codes:
> +==========
> +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 frames of 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.
> +
> +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 these codes and the BTN_TOOL_<name> and BTN_TOUCH codes 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
> +    codes should have a value of 1 during any synchronization frame.

I think the "Note" sentence needs an update.  I can interpret it as
defining 3 groups but only 2 exist.

Maybe: "Note that all BTN_TOOL_<name> codes (include these finger
touch codes) and the BTN_TOUCH code are orthogonal in purpose. "

Thats my only comment.  This doc will be great to have!

I'll propose a couple of example event sequences to add once this gets
committed.

Chris
> +
> +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.
> +
> +* KEY_SUSPEND, KEY_POWER:
> +  - These codes are reserved for the EV_PWR type.
> +
> +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
> +    should only be used while the tool is hovering, meaning in close proximity
> +    of the device. If the input device may be used freely in three dimensions,
> +    consider ABS_Z instead.
> +
> +* 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.
> +
> +EV_MSC:
> +----------
> +EV_MSC events are used for input and output events that do not fall under other
> +categories.
> +
> +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 key event used specifically for monitoring
> +power buttons and switches. The two codes in use are:
> +
> +* KEY_POWER:
> +  - Used to denote a power button event.
> +
> +* KEY_SUSPEND:
> +  - Used to denote a suspend button event.
> --
> 1.7.1
>
>
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