On Monday 20 February 2017 23:21:37 Petr Cvek wrote:

Hi,

Dne 20.2.2017 v 22:50 Dmitry Torokhov napsal(a):

quoted

On Mon, Feb 20, 2017 at 1:27 PM, H. Nikolaus Schaller
[off-list ref] wrote:

quoted

quoted

Am 20.02.2017 um 22:08 schrieb Pali Rohár [off-list ref]:

On Monday 20 February 2017 20:42:15 Pali Rohár wrote:

quoted

Hi Nikolaus!

On Monday 20 February 2017 17:50:04 H. Nikolaus Schaller wrote:

quoted

Hi Dmitry,

quoted

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)

quoted

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, 3x3 matrix which represent affine transformation can code inverted 
axis. This is IIRC what Xorg is doing.

But with information of min, max and current values plus resolution you 
cannot code information that axes are inverted (unless you misuse fact 
what is minimal and what maximal value). And this is what kernel 
provides for input device.

Affine transformation supported by Xorg is "stronger" as resolution 
provided by kernel.

-- 
Pali Rohár
pali.rohar@gmail.com