linux-kernel - Re: [PATCHv3 1/5] Input: add common DT binding for touchscreens

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Date:	Tue, 6 May 2014 01:04:12 +0200
From:	Sebastian Reichel <sre@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Tony Lindgren <tony@...mide.com>, linux-input@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/5] Input: add common DT binding for touchscreens

On Mon, May 05, 2014 at 12:51:39PM -0700, Dmitry Torokhov wrote:
> On Mon, May 05, 2014 at 12:41:26PM -0700, Tony Lindgren wrote:
> > * Sebastian Reichel <sre@...nel.org> [140425 16:56]:
> > > Add common DT binding documentation for touchscreen devices and
> > > implement input_parse_touchscreen_of_params, which parses the common
> > > properties and configures the input device accordingly.
> > > 
> > > The method currently does not interpret the axis inversion properties,
> > > since there is no matching flag in the generic linux input device.
> > > 
> > > Signed-off-by: Sebastian Reichel <sre@...nel.org>
> > > ---
> > >  .../bindings/input/touchscreen/touchscreen.txt     | 27 +++++++++++++++++
> > >  drivers/input/input.c                              | 34 ++++++++++++++++++++++
> > >  include/linux/input.h                              |  8 +++++
> > >  3 files changed, 69 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt
> > > 
> > > diff --git a/Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt b/Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt
> > > new file mode 100644
> > > index 0000000..d8e0616
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt
> > > @@ -0,0 +1,27 @@
> > > +General Touchscreen Properties:
> > > +
> > > +Optional properties for Touchscreens:
> > > + - touchscreen-size-x		: horizontal resolution of touchscreen
> > > +				  (in pixels)
> > > + - touchscreen-size-y		: vertical resolution of touchscreen
> > > +				  (in pixels)
> > > + - touchscreen-max-pressure	: maximum reported pressure (arbitrary range
> > > +				  dependent on the controller)
> > > + - touchscreen-fuzz-x		: horizontal noise value of the absolute input
> > > +				  device (in pixels)
> > > + - touchscreen-fuzz-y		: vertical noise value of the absolute input
> > > +				  device (in pixels)
> > > + - touchscreen-fuzz-pressure	: pressure noise value of the absolute input
> > > +				  device (arbitrary range dependent on the
> > > +				  controller)
> 
> Fuzz seems like linux-specific property, not generic one.

I don't know about the term "fuzz", but the idea is pretty generic
IMHO. It's similar to debouncing switches/buttons.

> > > + - touchscreen-inverted-x	: X axis is inverted (boolean)
> > > + - touchscreen-inverted-y	: Y axis is inverted (boolean)
> > 
> > We probably also need something to swap x and y depending on the
> > display orientation in addition to the touchscreen-inverted-x and y.
> > Just swapping x and y is not enough depending if we rotate by 270
> > degrees instead of 90 degrees.
> > 
> > Naturally that part can be added later.
> 
> So far we've been relying on upper layers (such as tslib) to perform
> such transformations rather than re-implementing it in every driver. Are
> we saying that we need to implement this in input core?

I would appreciate to add this later to move on with this patchset.
Having the N900's touchscreen working via DT in 3.16 would be nice
now that the display is working :)

-- Sebastian

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