linux-kernel - Re: [PATCHv2 1/5] Input: add common DT binding for touchscreens

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Message-ID: <20140407200022.GA20023@earth.universe>
Date:	Mon, 7 Apr 2014 22:00:23 +0200
From:	Sebastian Reichel <sre@...nel.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Dmitry Torokhov <dtor@...l.ru>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	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" <devicetree@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/5] Input: add common DT binding for touchscreens

On Mon, Apr 07, 2014 at 11:38:01AM -0500, Rob Herring wrote:
> On Sat, Apr 5, 2014 at 5:26 PM, Sebastian Reichel <sre@...nel.org> wrote:
> > 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.
> 
> Good.
> 
> [...]
> > +Optional properties for Touchscreens:
> > + - touchscreen-size-x          : horizontal resolution of touchscreen
> > + - touchscreen-size-y          : vertical resolution of touchscreen
> 
> While I like the consistency, x-size and y-size are already commonly
> used. Perhaps the common binding should have both and x-size/y-size be
> marked deprecated.

So you want me to add something like the following?

- x-size : deprecated name for touchscreen-size-x
- y-size : deprecated name for touchscreen-size-y

> > + - touchscreen-max-pressure    : maximum reported pressure
> > + - touchscreen-fuzz-x          : horizontal noise value of the absolute input device
> > + - touchscreen-fuzz-y          : vertical noise value of the absolute input device
> > + - touchscreen-fuzz-pressure   : pressure noise value of the absolute input device
> 
> What are the units or are they just an arbitrary range dependent on
> the controller? Several existing bindings appear to be in pixels, but
> that seems wrong to me.

x/y related properties: pixels
pressure related properties: arbitrary range dependent on the controller

> There's also these various properties that should have common versions created:
> 
> ti,x-plate-resistance and ti,x-plate-ohms (tsc2007)

I think this is ti specific. But I should probably name the tsc2005
property "ti,x-plate-ohms", so that its in sync with tsc2007.

> - rohm,flip-x             : Flip touch coordinates on the X axis
> - rohm,flip-y             : Flip touch coordinates on the Y axis
> - x-invert: invert X axis
> - y-invert: invert Y axis

like this?

- touchscreen-inverted-x: X axis is inverted
- touchscreen-inverted-y: Y axis is inverted
- x-invert: deprecated name for touchscreen-inverted-x
- y-invert: deprecated name for touchscreen-inverted-y

Inverting is currently not supported by the input system, though. So
adding support for it to input_parse_touchscreen_of_params() is not
trivial :/

> - contact-threshold:
> - moving-threshold:

I think those are hardware specific. The properties are currently
used by one driver, which writes them directly into some registers.
The DT binding does not give more information about them.

I think those should have been vendor-prefixed.

-- Sebastian

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