Comment 180 for bug 1651635

looking at the logs in attachment 260547:
* the ghost touch starts at 1216/0 (xmax/ymin) and is constant
* at 875.329542 it is at 1192/14
* It later *moves* to 1185/18 over several events and stays there. This pattern repeats multiple times

The highest distance from the edge is 1185 and 20, so roughly 3 and 2 mm, respectively. Note: this is from a manual analysis, not a scripted one so I may have missed a value. I'm assuming the others are the same, because in the end they can only be worse, if they're better than the above that's great ;)

For userspace this means:
* there isn't a single coordinate that we can blacklist
* we need some heuristics beyond 'maximum edge of the touchpad' because 3/2mm is a significant distance in. that heuristic runs the danger of interfering with real touches
* we can't just look at a touch and ignore it when it doesn't move - some of them move. Although it looks like they move late enough that we can pick them out before that happens.

Either way, the above would definitely require a model-specific quirk because we don't want to affect other devices. I wouldn't be surprised if windows papers over this accidentally, in the same way as the bug linked in comment 10 would probably paper over this. The windows bit is a guess though.

I'm going with Mario here and suspect this is defective hardware. If every XPS user would have this issue it'd be a different matter but fixing this has a nonzero cost for userspace.