[Letux-kernel] [PATCH v9 1/8] drivers:input:tsc2007: add new common binding names, pre-calibration, flipping and rotation

Pali Rohár pali.rohar at gmail.com
Mon Feb 20 20:42:15 CET 2017

Hi Nikolaus!

On Monday 20 February 2017 17:50:04 H. Nikolaus Schaller wrote:
> Hi Dmitry,
> > Input driver may set resolution for given axis in units per mm (or
> > units per radian for rotational axis ABS_RX, ABS_RY, ABS_RZ), and
> > if you check the binding, you can use "touchscreen-x-mm" and
> > "touchscreen-y-mm" to specify the size of entire touch surface and
> > set resolution from it so that userspace can calculate the proper
> > scaling factor.
> How is this information exposed by the kernel to user-space? By
> scanning the DT file or tree?

Set input_abs_set_res() from kernel. And in userspace call EVIOCGABS 
ioctl() on input device. Look at struct input_absinfo, you should have 
all needed information here. This is generic input interface, no DT is 

I hope that XServer is already using it for evdev devices...

For whole implementation look at evtest program. That should be good 
starting point for your userspace implementation.

While I'm watching this discussion... in my opinion kernel should just 
invert input axes (when needed) and should not do any other 
normalization or integer/floating-point re-calibration/re-calculation. 
If it correctly exports minimum value, maximum value and resolution then 
userspace can correctly re-scale input events to units which userspace 
needs (e.g. mapping into LCD screen pixels or whatever is needed).

Pali Rohár
pali.rohar at gmail.com
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