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SubjectRe: [PATCH v3 1/8] Input: add `REL_WHEEL_HI_RES` and `REL_HWHEEL_HI_RES`
On Wed, Dec 05, 2018 at 10:42:21AM +1000, Peter Hutterer wrote:
> 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>

> ---
> 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
>

--
Dmitry

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