(In reply to brett.hassall from comment #5)
> (In reply to Emil Velikov from comment #2)
> > If your bisection has gone right, you're looking at either
> > c39b487f195b93235ee76384427467786f7bf29f (if you're running amdgpu) or
> > b817634276f7f68c9d1d6d4a27117ff3c2f16956 (if you're on radeon).
> > 
> > lspci should tell you which one, and you should be able to revert either one
> > on top of 4.8.5. Once you confirm the commit causing the issue, please
> > change the component accordingly and CC the author - Alex Deucher.
> 
> Following the "git checkout tags/v4.8-rc3 -b bug" I reverted
> b817634276f7f68c9d1d6d4a27117ff3c2f16956. Power usage dropped by approx 4.5W
> (measured after login once system had settled, wifi not connected).

So apparently your system claims to support pcie pm (d3cold), but either
doesn't or it's disabled for some reason.