Re: [PATCH 1/3] input: tsc2007: Add pre-calibration, flipping and rotation

[Sebastian Reichel <sre@kernel.org>]

Hi,

On Thu, Jan 15, 2015 at 08:36:44AM +0100, Dr. H. Nikolaus Schaller wrote:
> > 1. Perform conversion in input core rather than individual drivers. I
> > think we should allocate a new bitmaps for some transformations and have
> > the code do X/Y flip/clip of the coordinates.
> 
> Do you have a suggestion where this should be (I have no clue how
> the input system works or is structured - we just know how to extend a
> driver that uses it)?
> 
> > 2. Standardize on bindings. We already have of-touchscreen.c doing
> > rudimentary parsing, we shoudl look into extending it rather than
> > creating myriad of driver-specific bindings.
> 
> Ok, looks reasonable.

Documentation is in 

Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt

> > Also, do we need swap and flip or do we simply need rotation (like the
> > proposed Broadcom iproc driver has)?
> 
> Well, since the DT should describe hardware, there are 3 sets of wires which
> can have a cross-over: X+ and X-, Y+ and Y-, X and Y.
>
> So IMHO hardware has no “rotation”, just crossover of wires. Rotation is an
> interpretation of the result of these connections in combination with some
> panel the touch is glued to and should therefore not be represented in the DT.
> 
> As a result we have proposed a scheme without explicit rotation. We specify what
> coordinates X- and X+ should report at their ends (min, max) because the DT
> programmer has to specify them anyways. Flipping is a result of defining these
> coordinates in an ascending or descending way. Only swapping of the X and Y
> wires can’t be implicitly defined so it has its own property. So the scheme we
> have proposed tries to optimize the efforts needed to adapt new boards and write
> DTs and focus the DT on hardware description.
> 
> As a bonus we also specify the min and max value to be reported for the touch
> pressure (Z axis) using the same basic principle.
> 
> And it is a pure add-on on top of the existing driver so that it attempts not
> to break existing device trees.

from what I can see there are no in-tree-users using any of the
new properties.

> Maybe could you accept it as a first step for this specific driver (and let’s do
> the big standardization work later on)?

That does not work, since you create an ABI.

-- Sebastian
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