Created Wednesday 23 September 2020
Ubuntu 18.04 desktop has a problem on HP laptops.... If you turn the machine upside-down or sideways, it will rotate the screen accordingly, but there is no force in heaven, hell or earth that will persuade it to turn right-side up.
The solution is to kill the accelerometers.
Add this to /etc/modprobe.d/blacklist.conf:
#HP Accelerometers are bad news on this model. blacklist hp_accel
Reboot and you're done.