Re: [PATCH] Input: atmel_mxt_ts - support KoD knob

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Jan 13, 2025 at 09:08:47PM +0100, Marek Vasut wrote:
> On 1/13/25 8:43 PM, Dmitry Torokhov wrote:
> > On Mon, Dec 23, 2024 at 08:03:24PM +0100, Marek Vasut wrote:
> > > Add support for T152 KoD knob events [1]. The KoD touch controller
> > > family supports up to two knobs attached to the glass. Each knob can
> > > be turned in either direction and the touch controller processes the
> > > event and reports the knob position for each knob. Each knob is also
> > > pressure sensitive, the pressure is reported as well. Each knob also
> > > supports center press and additional buttons, which are reported as
> > > BTN_0/BTN_1 for the center press for each knob, and BTN_A/BTN_B for
> > > the additional buttons on the knob.
> > > 
> > > The knob is similar to Dell Canvas 27 knob already supported by
> > > hid-multitouch, except it is non-removable and there can be up to
> > > two such knobs .
> > > 
> > > This implementation is extracted and heavily reworked from Atmel
> > > downstream patchset work by Michael <mksgong@gmail.com> from [2]
> > > branch master as of commit 9c77fbf32982 ("Merge pull request #35
> > > from atmel-maxtouch/20240103_HA_protocol_fixes").
> > > 
> > > [1] https://www.microchip.com/en-us/products/touch-and-gesture/maxtouch-touchscreen-controllers/kod-family
> > > [2] https://github.com/atmel-maxtouch/maXTouch_linux
> > > 
> > > Signed-off-by: Marek Vasut <marex@denx.de>
> > > ---
> > > Note: I am not sure whether reporting the second wheel as GAS/REL_HWHEEL
> > >        is the right thing to do, I don't think it is. Maybe there is some
> > >        better way to handle multiple knobs ?
> > 
> > How about creating separate input devices for these?
> This is what I had originally, but ... why ?
> 
> This is a single input device, touchscreen with up to two knobs , so why
> would it be multiple input devices ?

So as you can see it is hard to express the knobs purpose within a
single input device. Additionally (as far as I understand) knobs are
not connected to the touchscreen function but rather rotary encoders
just happened to be mounted on the touchscreen. They are not considered
contacts.

Therefore I think it makes sense to report them as 2 separate input
devices (maybe modeling after how drivers/input/misc/rotary-encoder.c
does things).

Thanks.

-- 
Dmitry