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April 3rd, 2022 23:00
U4320Q, U2520D, MST Daisy Chaining?
I have a question for @jphughan who has provided great answers on this thread.
I have a setup with a U4320Q next to a vertical U2520D - great setup with my desktop. Is it possible to drive the U4320Q from the DP out on the U2520D? I cannot get this to work with my desktop (1660 Super) although the DP on that is supposed to be 1.4a (doesn't really matter because there are multiple outputs on the 1660 super, but I was experimenting to try and understand that). I also can't get it to work on my laptop (pixelbook), but I wasn't really expecting it to. However, at some point I would like to get a new laptop and it would be nice to be able to drive both monitors with a one cable usb-c connection to the U2520D. Explanations of MST or what is required are hard to find on the internet (at least for me, though it's possible I just don't have enough knowledge understand them).
Thank you.
jphughan
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April 3rd, 2022 23:00
Hey @Omar Daal , glad you've found my other answers useful. In terms of your question, I actually would have expected that to work, but if it's not, then my only guess is that the U2520D's DP output might only support DP 1.2, even though I realize its input supports DP 1.4. And the only reason I suggest this possibility is that I remember a PM exchange with a Dell contact on this forum suggesting that this design had been implemented on some other Dell display, I think the U2719DC. Ironically that meant that there was no benefit whatsoever in the DP input supporting DP 1.4, but that's apparently how the display was set up. Maybe that combination was a quirk of the third party supplier chips available at the time or something.
And the other possibility is some strange firmware glitch somewhere. I remember having trouble getting a triple 1080p 60 Hz setup working from a DP 1.2 output on a Dell E-Port Dock when using a Latitude E5550 -- even though running a dual display chain from one dock output and the third display from the other dock output worked fine and the dock itself only had a single DP 1.2 interface coming from that system. So two setups that shouldn't have made a practical difference nonetheless behaved differently.
In terms of running both displays from a single USB-C connection from your system, that actually adds another wrinkle. That display would default to setting up the USB-C link for USB 3.x data + video, but running USB 3.x cuts your video bandwidth in half, and I'm not sure half of a DP 1.4 interface is enough for 4K 60 Hz + 1440p 60 Hz. (I didn't do the math.) The U2520D does have a USB-C Prioritization option that you can use to limit the display to USB 2.0 data + video, in which case you'd have a full DP interface of video bandwidth available -- assuming you'd be ok with only USB 2.0 data to the display's built-in USB ports -- but if your desktop can't run that daisy chain either, a laptop might not fare any better. The last option would be a USB-C MST hub that supported DisplayPort 1.4, plus a system that did as well. This one is a good example because it supports not only DP 1.4 but also DisplayPort DSC, which allows even higher-end setups if the laptop supports it as well. And it even has a USB-C power passthrough port. The one thing you would lose in a setup like this would be any sort of USB data over USB-C, which could become inconvenient if you wanted a docking station type of setup with a single cable connection to your laptop.