> Am 20.02.2017 um 22:08 schrieb Pali Rohár <pali.rohar@xxxxxxxxx>: > > 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) It is questionable why it should do that at all then. User-Space can also easily do it. Either the driver should provide raw data only or if it does pre-processing (scaling by +/-1), why exclude pre-scaling by other factors? >> 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@xxxxxxxxx
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