Hi,

[...]

quoted

Hm. Why not touching pixel (0,0) on the touch is always pixel (0,0)
on the screen and touching pixel (639,479) is always (639,479)?

Important is that there is no 1:1 mapping between input evdev device
and drm/fb output device. These are two independent devices. There is
no connection between screen and touch. So such presumption should
not be done in kernel. You can do that in userspace.

But at least it can be told to userspace that these two devices are
connected. That information should be specified in devicetree because
it is not auto-detectable.

Lets take e.g. touchpad. It acts similarly as touchscreen input device
(both reports absolute positioned touch events), but touchpad is not
connected with screen. And from kernel point of view these devices are
both input and absolute positioned.

It looks like the whole problem is there that you wanted to do this
mapping for your hardware in kernel. And this is not what is kernel
doing or should do. Moreover I know people who are using integrated
touchscreen on laptop as (touch) input device for external monitor.
And in this configuration it does not make any sense to map
touchscreen input to pixels of integrated LCD touchscreen (as
external monitor could have different resolution as integrated LCD
touchcreen).
  

Interesting example. But then you also do not need flipping/rotation
because the angle between your screen and your absolute position device
is not fixed.

Regards,
Andreas