Heh, got a pretty same issue. Although I've got my patch for MSI R7 370 Armor
2X proposed and present in 4.3, I've got some weird issues with dpm, like
complete system hang + black screen after some time using PC (dpm enabled), so
I have to put radeon.dpm=0 to params to boot and use the system somehow.
However, it looks like an ID conflict in si_dpm.c because of a newer patch to
that file (check github), because my GPU works flawlessly with 4.2.X kernel +
my patch applied. Here's my bug, if someone's interested:
https://bugs.freedesktop.org/show_bug.cgi?id=92865