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.hutte...@who-t.net> --- 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: * 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 ------ 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) -- 2.19.2
