Recently some of my coworkers and I experienced an issue with using the upper left touchpad button on our Dell Latitude E7470 and similar laptops (E5xxx from the current generation). Some time in January we could no longer hold down this button and select text with the touchpad. Using the left button below the touchpad still worked. This hit my coworker running Fedora and myself running Debian/stretch. So I first thought that it's likely a libinput issue (same version in Debian/stretch and Fedora and I recently pulled that in as an update), somehow blacklisting the upper left key because it's connected to the trackpoint. So I filled #99594 upstream. While this was not very helpful at first, and according to Peter very unlikely to be related to libinput, another coworker using Debian/jessie found this issue to hit him when he upgraded the backports kernel in use from 4.8 to 4.9. That finally led to the conclusion that it's a bug in the Linux alps driver, which is already fixed in 4.10 and probably 4.9.6.
Until the Debian kernel team pulls in a fresh 4.9 point release I'm using 4.10-rc6 from experimental. For Debian/jessie + backports kernel user it might be more convenient to just stay at 4.8 in case this issue annoys you.
Kudos to Peter, Benjamin, TW and WW for the help in locating the origin of this issue!
Lessons learned:
- I should've started with the painful downgrade of xorg and libinput via snapshot.d.o before opening the bugreport.
- A lot more of the touchpad related hardware support is nowadays in the kernel and not in the xorg layer. Either that was just my personal historic misunderstanding, or it was different 10 years ago.
- There is an interesting set of slides from Benjamin related to debuging input device issues.