Skip to content

Commit

Permalink
Input: document the units for resolution of size axes
Browse files Browse the repository at this point in the history
Today, the resolution of size axes is not documented. As a result, it's
not clear what the canonical interpretation of this value should be. On
Android, there is a need to calculate the size of the touch ellipse in
physical units (millimeters).

After reviewing linux source, it turned out that most of the existing
usages are already interpreting this value as "units/mm". This
documentation will make it explicit. This will help device
implementations with correctly following the linux specs, and will
ensure that the devices will work on Android without needing further
customized parameters for scaling of major/minor values.

Signed-off-by: Siarhei Vishniakou <svv@google.com>
Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20220520084514.3451193-1-svv@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
  • Loading branch information
Siarhei Vishniakou authored and Dmitry Torokhov committed Jul 9, 2022
1 parent 3de93e6 commit 2a96271
Showing 1 changed file with 7 additions and 4 deletions.
11 changes: 7 additions & 4 deletions include/uapi/linux/input.h
Original file line number Diff line number Diff line change
Expand Up @@ -78,10 +78,13 @@ struct input_id {
* Note that input core does not clamp reported values to the
* [minimum, maximum] limits, such task is left to userspace.
*
* The default resolution for main axes (ABS_X, ABS_Y, ABS_Z)
* is reported in units per millimeter (units/mm), resolution
* for rotational axes (ABS_RX, ABS_RY, ABS_RZ) is reported
* in units per radian.
* The default resolution for main axes (ABS_X, ABS_Y, ABS_Z,
* ABS_MT_POSITION_X, ABS_MT_POSITION_Y) is reported in units
* per millimeter (units/mm), resolution for rotational axes
* (ABS_RX, ABS_RY, ABS_RZ) is reported in units per radian.
* The resolution for the size axes (ABS_MT_TOUCH_MAJOR,
* ABS_MT_TOUCH_MINOR, ABS_MT_WIDTH_MAJOR, ABS_MT_WIDTH_MINOR)
* is reported in units per millimeter (units/mm).
* When INPUT_PROP_ACCELEROMETER is set the resolution changes.
* The main axes (ABS_X, ABS_Y, ABS_Z) are then reported in
* units per g (units/g) and in units per degree per second
Expand Down

0 comments on commit 2a96271

Please sign in to comment.