I also had some problems to get 4k@60hz on my television with Xubuntu 16.04 64 bit and an Asus Radeon RX 460 graphics card. After some configuration it works nearly perfectly now. Here is what I did and what is important:
- Check if you selected the right HDMI slot at your television. On my TV only one slot supports 4k@60hz resolution.
- On my TV I had to enable "deep color" for the correct HDMI slot
- Set the HDMI slot of the TV in the TV settings to "slot connected to PC" if this option is available
- Be sure to have a HDMI 2.0 cable or higher attached
- Install the latest amd gpu pro driver from the amd support page
- Correct the installation of the driver if necessary. I had to add symlinks to the vdpau libs otherwise accelerated video decoding is not working. I also had to change the "10-amdgpu-pro.conf" config file in order to avoid tearing in videos.
- On Xubuntu I then have to activate the screen in the settings manager. This is a little annoying because often I have to try this multiple times until I get 4k@60hz resolution. This is probably a little bug but at least it is working in the end. Try to disable and enable the screen in the video settings or change the framerate lower and back to 60hz.
I have not installed the LunarG Vulkan loader yet.
Unfortunately there is no gpu accelerated decoding for videos in Firefox on Linux but after enabling OpenGL Off-Main-Thread Compositing I can at least watch 4k@30hz streams stutter-free on an Intel Core i5 750 CPU (4 physical cores at 2.7 GHz). The VLC player for example supports gpu accelerated video decoding, post-processing and rendering with version 2.2.0.
By the way I only have PCI-Express 2.0 slot and 3.0 is required for my graphics card but it's working good anyway even if I have not 100% performance.
I hope this helps someone :) Took me lots of hours to get everything working...