(In reply to Alex Deucher from comment #7)
> (In reply to Duncan Roe from comment #6)
> > (In reply to Duncan Roe from comment #3)
> > > halt is fine btw, it's only reboot that breaks.
> > > Do you want extra debug turned on for dmesg?
> > 
> > At Linux 19.0-rc8, power button / halt command also fails. The backlight
> > goes off but the power stays on.
> 
> Can you bisect that?  Is it the same commit?

It is the same commit i.e. 0a1d565 built from the stable tree consistently
fails to power off. 30cdbfa *sometimes* fails to power off - I think I have
seen 2 fails in6 reboots (my spreadsheet isn't set up to count results (yet)).