Comment # 86 on bug 76490 from Daniel Exner

Tried kernel 4.4.0-rc4 with 

"drm/radeon: load different smc firmware on some SI variants"

and 

"drm/radeon: print pci revision id as well as pci ids"

applied.

The good news: this kernel boots just fine:

[    3.120205] [drm] radeon kernel modesetting enabled.
[    3.135919] [drm] initializing kernel modesetting (PITCAIRN 0x1002:0x6810
0x1462:0x3036 0x00).

But if I remove line 2927 from drivers/gpu/drm/radeon/si_dpm.c the initial
problems return: boot fails.