https://bugzilla.kernel.org/show_bug.cgi?id=51381
--- Comment #31 from Alex Deucher alexdeucher@gmail.com --- Ok, it appears powering up the dGPU has never worked properly on your system. As a workaround for now you can disable runpm by adding radeon.runpm=0. I can add a quirk to the driver to disable runpm on your system by default until someone figures out how to fix it.