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

From: Dmitry Torokhov
Date: Mon Feb 20 2017 - 17:24:54 EST

On Mon, Feb 20, 2017 at 2:21 PM, Petr Cvek <petr.cvek@xxxxxx> wrote:
> Hi,
> Dne 20.2.2017 v 22:50 Dmitry Torokhov napsal(a):
>> On Mon, Feb 20, 2017 at 1:27 PM, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> wrote:
>>>> Am 20.02.2017 um 22:08 schrieb Pali RohÃr <pali.rohar@xxxxxxxxx>:
>>>> On Monday 20 February 2017 20:42:15 Pali RohÃr 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.
>> Because the task of the kernel is to provide unified view of the
>> hardware. Axis swapping and inversion is needed to that "up" is always
>> "up" and "right" is always "right".
> Actually my Xorg calibration 3x3 matrix is fine with both axis inverted (on TSC2046).

Yes, you can make it work for your touchscreen as long as you know
that it inverted somehow. How you gain this knowledge is the question.