https://bugzilla.kernel.org/show_bug.cgi?id=61891
--- Comment #13 from madcatx@atlas.cz --- "acpiphp.disable=1" in the kernel bootline fixes the problem for me. The Radeon is reported as off in vgaswitcheroo and the laptop draws less power. The DIS even powers up and down correctly with DRI_PRIME.
Acpidump provided