linux-kernel - Re: [PATCH v3 1/8] Input: add `REL_WHEEL_HI_RES` and `REL_HWHEEL_HI

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Date:   Thu, 6 Dec 2018 14:56:41 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Peter Hutterer <peter.hutterer@...-t.net>
Cc:     linux-input@...r.kernel.org, Jiri Kosina <jikos@...nel.org>,
        Harry Cutts <hcutts@...omium.org>,
        torvalds@...ux-foundation.org,
        Nestor Lopez Casado <nlopezcasad@...itech.com>,
        linux-kernel@...r.kernel.org,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [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@...-t.net>

Acked-by: Dmitry Torokhov <dmitry.torokhov@...il.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