[PATCH v3 1/8] Input: add `REL_WHEEL_HI_RES` and `REL_HWHEEL_HI_RES`

From: Peter Hutterer
Date: Tue Dec 04 2018 - 19:42:57 EST

This event code represents scroll reports from high-resolution wheels and
is modelled after the approach Windows uses. The value 120 is one detent
(wheel click) of movement. Mice with higher-resolution scrolling can send
fractions of 120 which must be accumulated in userspace. Userspace can either
wait for a full 120 to accumulate or scroll by fractions of one logical scroll
movement as the events come in. 120 was picked as magic number because it has
a high number of integer fractions that can be used by high-resolution wheels.

For more information see

These new axes obsolete REL_WHEEL and REL_HWHEEL. The legacy axes are emulated
by the kernel but the most accurate (and most granular) data is available
through the new axes.

Signed-off-by: Peter Hutterer <peter.hutterer@xxxxxxxxx>
No changes since v1

Documentation/input/event-codes.rst | 21 ++++++++++++++++++++-
include/uapi/linux/input-event-codes.h | 2 ++
2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
index a8c0873beb95..b24b5343f5eb 100644
--- a/Documentation/input/event-codes.rst
+++ b/Documentation/input/event-codes.rst
@@ -190,7 +190,26 @@ A few EV_REL codes have special meanings:

- These codes are used for vertical and horizontal scroll wheels,
- respectively.
+ respectively. The value is the number of detents moved on the wheel, the
+ physical size of which varies by device. For high-resolution wheels
+ this may be an approximation based on the high-resolution scroll events,
+ see REL_WHEEL_HI_RES. These event codes are legacy codes and
+ REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where
+ available.
+ - High-resolution scroll wheel data. The accumulated value 120 represents
+ movement by one detent. For devices that do not provide high-resolution
+ scrolling, the value is always a multiple of 120. For devices with
+ high-resolution scrolling, the value may be a fraction of 120.
+ If a vertical scroll wheel supports high-resolution scrolling, this code
+ will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL
+ and REL_HWHEEL may be an approximation based on the high-resolution
+ scroll events. There is no guarantee that the high-resolution data
+ is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL
+ event.

diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
index 3eb5a4c3d60a..265ef2028660 100644
--- a/include/uapi/linux/input-event-codes.h
+++ b/include/uapi/linux/input-event-codes.h
@@ -716,6 +716,8 @@
* the situation described above.
#define REL_RESERVED 0x0a
+#define REL_WHEEL_HI_RES 0x0b
+#define REL_HWHEEL_HI_RES 0x0c
#define REL_MAX 0x0f
#define REL_CNT (REL_MAX+1)