(In reply to Michel Dänzer from comment #7)
> According to the log file, the ASUS monitor only lists the 60 Hz 1920x1080
> mode in its EDID. So it seems clear that's what the monitor wants to be fed,
> but for some reason we don't seem to be generating it properly.
> 
> Any chance you can try if a kernel built from the amd-staging-4.12 or
> amd-staging-drm-next branch of https://cgit.freedesktop.org/~agd5f/linux/
> with CONFIG_DRM_AMD_DC=y works better?

Thank you, It works :) 

I thought amdgpu-staging kernel was only needed for their PRO driver, so i
never had the idea to try it.