[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 22:08:50 CET 2017

On Monday 20 February 2017 20:42:15 Pali Rohár wrote:
> 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 needed.

Looking at kernel code... via EVIOCSABS ioctl() you can even set 
resolution from userspace for specified input device.

So this could be potentially used for calibrating input device from 
userspace? (In case DT data will not fully match current HW)

> 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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