I've got my Thinkpad T460p connected with 2 external displays. One is Samsung U28H75X which supports 4k resolution, the other is AOC Q2577W which supports 2k resolution.
I use DP port to connect the Samsung and HDMI port to connect the AOC.
I am with the latest MFG driver, 18.104.22.16864.
The problem is that I am not able to set up the Samsung at 4k@60hz while the AOC at 2k@60hz. I tried many ways and multiple times but it seems it only settles with Samsung 4k@30hz and AOC 2k@60hz. Could anyone advise? Thanks in advance.
The only way this makes sense is if the DP and HDMI connectors are connected to the same DP output from the processor. It seems odd that they'd have an MST Hub IC (to split one DP into two DP outputs) and a LSPcon IC (to convert from DP to HDMI), when the processor has two DP outputs that they could have used (the third is used for embedded screen). At this point, I can only suggest that you call Lenovo and ask them what they have done.
Thanks for the reply. Actually this T460p laptop only has one HDMI output. In order to use 2 external displays, I bought a Thinkpad Ultra Dock which provides 2 DP output ands 1 extra HDMI output port. I use one DP output to connect the Samsung 4k display, because base on what I've tested, that's the only way to enable 4k@60p with the Samsung. And I tried both the other DP and the HDMI on the dock to connect with the AOC. The results are same. When I set up the Samsung at 4k@60p, the 2K resolution options are all gone for the AOC monitor. Only when I lower down the resolution or refresh frequency for the Samsung, the 2k options go back to available.
This does not affect my answer. You have monitor outputs on this dock that share a single DP stream. This stream is compliant with the DisplayPort 1.2 (HBR2) standard and thus is capable of supporting only a single 4K monitor at 60Hz. After connecting the 4K monitor at 60Hz, there is (barely) enough bandwidth remaining to support a 1080p monitor at 60Hz but there is not enough to support a 2K monitor at 60Hz.
Now, you could connect the 4K monitor to this dock and the 2K monitor to the HDMI output on the laptop. Both would then be using separate DP streams and thus able to run at 60Hz. This makes "going mobile" slightly more involved as you would have yet another thing to unplug and later plug back in.
By the way, you cannot connect the Samsung TV via the dock's HDMI connector because this connector only supports HDMI 1.4 and thus can only support 4K at 30Hz. You need HDMI 2.0 support to enable 4K at 60Hz.