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

H. Nikolaus Schaller
2017-02-20T20:35:18Z

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Hi Pali,

> Am 20.02.2017 um 20:42 schrieb Pali Rohár <pali.rohar@gmail.com>:
>
> 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.

This assumes that I can and want to write a graphics system myself.

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

No idea if it does. It is a black box for me out of our control.

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

The problem I have is that *I* have no userspace implementation and
the GTA04 project does not want to enforce one. We have several different
ones: X11 based (LXDE and others), Qt (fb based), Replicant to name some.

All have the same problem to be solved once. The common denominator for
a solution are 2 lines of code in the kernel plus some DT properties
you need anyways if calibration should be automated in userland.

>
> 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).

It can, but afaik it does not yet. And if it does, it does it in a plethora
of different implementation states. That is the reason why we want to solve
it once for all userlands in the kernel and not rely on user-space help.

Surely, userland can do a lot of things. It could also do the whole
file system stuff (FUSE).

A more input device related example comes to my mind: userland could do
keyboard mapping completely. It would suffice if the kernel presents
some x/y coordinates or gpio-numbers for buttons and user-space could map.
Still there is a (pre-)mapping to Key-Codes. And yes, they are mapped a second
time in userland if needed, but it works sufficiently well if not done.

BR and thanks,
Nikolaus

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