(In reply to Kimmo from comment #14)
> Confirming still similar problem (Screen stays black while trying resume
> from suspend)
> 2x DELL u2415h + display port daisy chain + RX480 (amdgpu 18.0.1-2)

Actually need to correct myself. The suspend problem seems to be fixed and
working ok for me so far. Problem seems to be more related if Dell monitor is
allowed to shutdown by itself due to inactivity, but not sure if it has any
relations to amdgpu. Using KDE plasma desktop 5.13.3. Sorry for inconvenience.