Can't hand back to hardware control
It seems once manual control has been engaged, it's not possible to hand control back over to the hardware. Neither by writing to 2 to pwm*_enable, nor by writing level auto to /proc/acpi/ibm/fan, nor by letting the watchdog try to do it.
Must be a bug somewhere.
Do you see any errors when writing 2 to pwm*_enable? Is 2 visible under pwm*_enable after write?
For me (X1 extreme 1st gen, EC/bios version: N2E) writing 2 to pwm*_enable works fine. Reverts to hardware control.
Btw, check if it enables full speed when writing 0 to pwm*_enable
Full-speed works fine. I suspect something got screwed up during my experiments. Will do a reboot later and check things again.