Corrupted output at 4K resolutions

Jan 21, 2017
I have an HD Graphics 4600 driving a 4K display at 30Hz using HDMI. The only way that I can get this to work is to use whatevergreen WEG with patches to the framebuffer size.

If I don't patch the framebuffer size then it is not possible to run at 4K an that option is not avaiable. If I patch the framebuffer to 32Mb then every time I startup the display is garbled with ever second line being blank. If I change display mode to a something like 2K using DisplayManager (you can see the drop down list) the display is fine. If I choose the 3820x2160@30Hz HDMI mode after the first change the display is ok.