linux-kernel - Re: [PATCH 2/4] dt-bindings: touchscreen: add virtual-touchscreen and virtual-buttons properties

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Date:   Fri, 12 May 2023 08:25:53 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Javier Carrasco <javier.carrasco@...fvision.net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Henrik Rydberg <rydberg@...math.org>,
        Bastian Hecht <hechtb@...il.com>,
        Michael Riesch <michael.riesch@...fvision.net>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: touchscreen: add virtual-touchscreen and
 virtual-buttons properties

On 11/05/2023 12:28, Javier Carrasco wrote:
> On 11.05.23 11:45, Krzysztof Kozlowski wrote:
>> On 10/05/2023 15:50, Javier Carrasco wrote:
>>> The virtual-touchscreen object defines an area within the touchscreen
>>> where touch events are reported and their coordinates get converted to
>>> the virtual origin. This object avoids getting events from areas that
>>> are physically hidden by overlay frames.
>>>
>>> For touchscreens where overlay buttons on the touchscreen surface are
>>> provided, the virtual-buttons object contains a node for every button
>>> and the key event that should be reported when pressed.
>>
>> Hm, I don't understand - are these separate physical buttons? If so, why
>> would they be part of touchscreen? Where do the wires go?
> Those buttons are actually printed on some overlays which are mounted on
> top of the touchscreen and  they are used to provide a predefined
> functionality to that touchscreen region. Any touchscreen with such a
> physical overlay with buttons printed on them or clipped touchscreen
> areas might use this functionality.
> 
> These buttons are actually physical i.e. printed and with a given
> functionality, but still part of the touchscreen as the physical device
> is not aware of them. Therefore they only make sense in the touchscreen
> context.

So basically you still have the same touchscreen under the buttons and
these are not separate devices. Whether someone put a sticker on
touchscreen, does not really change hardware behavior and it's up to
system to handle this. What you are trying to do here is to create
virtual buttons through Devicetree and DT is not for that.

Best regards,
Krzysztof