[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 23:04:22 CET 2017

On Monday 20 February 2017 22:27:39 H. Nikolaus Schaller wrote:
> > Am 20.02.2017 um 22:08 schrieb Pali Rohár <pali.rohar at gmail.com>:
> > 
> > On Monday 20 February 2017 20:42:15 Pali Rohár wrote:
> >> 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?

Via resolution property which is in that EVIOCSABS ioctl() you specify 
value which represent unit per mm. So you cannot do full rescaling like 
via affine transformation. Specially you cannot swap axes or invert it.

As such thing is not supported by current kernel <--> userspace API it 
needs to be done in kernel.

Moreover I see that this is already handled by kernel's of_touchscreen.c 
code via DT properties: touchscreen-inverted-* touchscreen-swapped-x-y

And... I'm not sure but I think that linux exports absolute input 
devices with coordinates where point (0,0) is mapped as left upper 

> >> 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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