[PATCH 1/4] input: touchscreen: Add generic touchscreen softbutton handling code

[Hans de Goede]

Hi,

On 01-08-16 19:41, Dmitry Torokhov wrote:
> On Mon, Aug 01, 2016 at 11:54:30AM -0500, Rob Herring wrote:
>> On Sun, Jul 31, 2016 at 05:23:07PM +0200, Hans de Goede wrote:
>>> Some touchscreens extend over the display they cover and have a number
>>> of capacative softbuttons outside of the display the cover.
>>>
>>> With some hardware these softbuttons simply report touches with
>>> coordinates outside of the normal coordinate space for touches on the
>>> display.
>>>
>>> This commit adds a devicetree binding for describing such buttons in
>>> devicetree and a bunch of helper functions to easily add support for
>>> these to existing touchscreen drivers.
>>>
>>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>>> ---
>>>  .../bindings/input/touchscreen/softbuttons.txt     |  58 +++++++++
>>>  drivers/input/touchscreen/Makefile                 |   2 +-
>>>  drivers/input/touchscreen/softbuttons.c            | 145 +++++++++++++++++++++
>>>  include/linux/input/touchscreen.h                  |   9 ++
>>>  4 files changed, 213 insertions(+), 1 deletion(-)
>>>  create mode 100644 Documentation/devicetree/bindings/input/touchscreen/softbuttons.txt
>>>  create mode 100644 drivers/input/touchscreen/softbuttons.c
>>>
>>> diff --git a/Documentation/devicetree/bindings/input/touchscreen/softbuttons.txt b/Documentation/devicetree/bindings/input/touchscreen/softbuttons.txt
>>> new file mode 100644
>>> index 0000000..3eb6f4c
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/input/touchscreen/softbuttons.txt
>>> @@ -0,0 +1,58 @@
>>> +General Touchscreen Softbutton Properties:
>>> +
>>> +Some touchscreens extend over the display they cover and have a number
>>> +of capacative softbuttons outside of the display the cover.
>>> +
>>> +Some of these softbuttons simply report touches with coordinates outside of
>>> +the normal coordinate space for touches on the display. This binding is for
>>> +describing such buttons in devicetree.
>>> +
>>> +Each softkey is represented as a sub-node of the touchscreen node.
>>> +
>>> +Required subnode-properties:
>>> + - label			: Descriptive name of the key.
>>> + - linux,code			: Keycode to emit.
>>> + - softbutton-min-x		: X start of the area the softbutton area covers
>>> + - softbutton-max-x		: X end of the area the softbutton area covers
>>> + - softbutton-min-y		: Y start of the area the softbutton area covers
>>> + - softbutton-max-y		: Y end of the area the softbutton area covers
>>
>> This generally looks fine to me, but I am wondering one thing. If the
>> buttons are located at the origin of an axis, can we handle that case? I
>> don't think you can unless you assume softbutton-max-? is 0 for the
>> touchscreen. To put it another way, you have a gap from 1024 to 1084
>> which you can't express for buttons at the origin unless you do negative
>> numbers.
>
> I do not this this should be done in kernel: I do not see nay difference
> in softbuttons or sliders or circular controls or... They are not
> controller-specific and I think are better handled in userspace. We do
> that for Synaptics touchpads with softbuttons, we can do that for other
> controllers.
>
> Also, what is or stance when there is no bezel and we sill want to have
> the softbutons (i.e. all Nexus phones and tablets)?

Maybe softbuttons is not the best name (I googled and it seemed to match),
so first lets make clear what I'm talking about here, I wrote this patch-set
for this tablet:

https://content.hwigroup.net/images/products_xl/157078/dserve-dsrv-9703c.jpg

I decided to make it generic, since it seemed to me that there will likely
be other hardware which is similar (but uses a different touch screen
controller) out there, so keeping this generic seemed best.

Now back to the kernelspace vs userspace solution question, if you look at
the picture you will see 3 clearly marked buttons on the front of the tablet,
outside of the display: menu, home and back. These are not buttons which get
generated / drawn on the display when you touch the bottom of the screen, these
are separate single-purpose buttons which happen to report presses via the
touchscreen controller then via a separate hw mechanism.

If these buttons used a separate capacative button controller as used in
e.g. capacitive numpads, say something like this:

http://www.ebay.com/itm/2PCS-TTP223-Capacitive-Touch-Switch-Button-Self-Lock-Module-for-Arduino-/131662428748

Then there would be no question that this belongs in the kernel. I do not
see how these are any different really. These cannot be runtime re-configured,
they are separate dedicated buttons which happens to report presses via
the touchscreen controllers.

There also is the question of hardware description, no matter where we
put support for this, we need some place were we describe the presence
of these buttons to the software bits which end up dealing with them.

And we already have a mechanism for describing "fixed" hardware for a
certain model machine / board in the form of devicetree. To me putting
the hardware description for this anywhere but in devicetree makes
no sense because then we start scattering the description of a single
device-type over multiple places which seems like a bad idea.

And once we decided to put the description in devicetree, then dealing
with this in the kernel becomes the logical thing to do.

Regards,

Hans


p.s.

One other example of buttons like these are those on the nexus one:

http://www.informatica.com.do/7BZ-PortalImageUpload/image/2010151059110.google-nexus-one-01.jpg

Note I'm not saying this binding will work for those, I've no idea how
they are hooked up, but they are the same in that they are really
4 dedicated separate buttons which happen to be part of the main digitizer.