- Why is 4k60/UHD60 not supported (or detected) when mini-DP is connected directly to the GPU (but works when connected to eGPU mini-DP port)?
- Is there a way to disable AMD Xconnect for eGPU systems, so my laptop can just use the mini-DP port with the Intel GPU? (There is a major bottleneck displaying full-motion video over the host controller, and I think this would help a lot.)
I have tried all three of the latest driver releases available on the AMD driver download page for Radeon HD 7970, and none of them allow the use of 3840x2160 @ 60Hz (UHD60) when connected to the GPU directly, despite being listed as capable of this resolution. I have confirmed that not only is my display supports UHD60, but the same DP-to-HDMI adapter I'm using has also worked at UHD60, too.
What's even stranger is given by my configuration: I put the 7970 in an eGPU enclosure with a USB-C Thunderbolt 3 connection, and it has a mini-DP connection on its host controller board. When I connect the mini-DP adapter from the 7970 to the host controller, the GPU is detected, AMD Xconnect is launched, and the 60Hz mode is available to drive the display. Of course, with Xconnect, the GPU doing the rendering is the 7970, and the output signal to the UHD60 display is going back over the PCIe connection to the host controller to be output to the display (at best) or (at worst) sent back over the Thunderbolt 3 connection to the integrated Intel GPU, then sent back over the TB3 cable to the controller to be routed over the mini-DP connector.
It makes no sense to me that the UHD60 (and 4k60) modes are NOT available when mini-DP is connected directly to the card, but somehow they appear magically supported through a needlessly complex topology of Thunderbolt/DisplayPort hardware.
If more information is needed to address my problem, please let me know. If it's detailed debug information you need, an explanation of how to retrieve it may be necessary. Thanks.