input: add MT_TOOL_DIAL

A dial is a tool you place on a multitouch surface which reports its
orientation or a relative angle of rotation when rotating its knob.

Some examples are the Dell Totem (on the Canvas 27"), the Microsoft Dial,
or the Griffin Powermate, though the later can't be put on a touch surface.

We give some extra space to account for other types of fingers if we need
(MT_TOOL_THUMB)

Slightly change the documentation to not make it mandatory to update each
MT_TOOL we add.
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/input/multi-touch-protocol.rst

@@ -310,12 +310,12 @@ ABS_MT_TOOL_Y
 ABS_MT_TOOL_TYPE
     The type of approaching tool. A lot of kernel drivers cannot distinguish
     between different tool types, such as a finger or a pen. In such cases, the
-    event should be omitted. The protocol currently supports MT_TOOL_FINGER,
-    MT_TOOL_PEN, and MT_TOOL_PALM [#f2]_. For type B devices, this event is
-    handled by input core; drivers should instead use
-    input_mt_report_slot_state(). A contact's ABS_MT_TOOL_TYPE may change over
-    time while still touching the device, because the firmware may not be able
-    to determine which tool is being used when it first appears.
+    event should be omitted. The protocol currently mainly supports
+    MT_TOOL_FINGER, MT_TOOL_PEN, and MT_TOOL_PALM [#f2]_.
+    For type B devices, this event is handled by input core; drivers should
+    instead use input_mt_report_slot_state(). A contact's ABS_MT_TOOL_TYPE may
+    change over time while still touching the device, because the firmware may
+    not be able to determine which tool is being used when it first appears.
 
 ABS_MT_BLOB_ID
     The BLOB_ID groups several packets together into one arbitrarily shaped

include/uapi/linux/input.h

@@ -270,10 +270,11 @@ struct input_mask {
 /*
  * MT_TOOL types
  */
-#define MT_TOOL_FINGER		0
-#define MT_TOOL_PEN		1
-#define MT_TOOL_PALM		2
-#define MT_TOOL_MAX		2
+#define MT_TOOL_FINGER		0x00
+#define MT_TOOL_PEN		0x01
+#define MT_TOOL_PALM		0x02
+#define MT_TOOL_DIAL		0x0a
+#define MT_TOOL_MAX		0x0f
 
 /*
  * Values describing the status of a force-feedback effect