Input: add `REL_WHEEL_HI_RES` and `REL_HWHEEL_HI_RES`

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
https://docs.microsoft.com/en-us/previous-versions/windows/hardware/design/dn613912(v=vs.85)

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@who-t.net>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Verified-by: Harry Cutts <hcutts@chromium.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
This commit is contained in:
Peter Hutterer 2018-12-05 10:42:21 +10:00 committed by Benjamin Tissoires
parent e195ca6cb6
commit 52ea899637
2 changed files with 22 additions and 1 deletions

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@ -190,7 +190,26 @@ A few EV_REL codes have special meanings:
* REL_WHEEL, REL_HWHEEL:
- 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.
* REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES:
- 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.
EV_ABS
------

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@ -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)