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Vostro 7590 Dual Monitor low resolution problem with Daisy Chain MST via USB-C Thunderbolt 3
Hi,
I am using Dell Vostro 7590 (i7 9750h and GTX 1650) which has one thunderbolt 3 usb-c port and i want to connect two WQHD Displays (Philips 276B1) with 2.560 x 1.440 at 60 Hz with Displayport Daisy Chaining.
According to the Specs this should work with WQHD, because Thundebolt3 should have Displayport 1.2 with 4 links and MST. The Displays have Displayport 1.4 so this should work also.
But in reality it only works with FHD (1920 x1080) mode. In clone mode it is also possible with WQHD with daisy chaining.
The USB-C cable equiped with the Display is conected between notebook and first display usb c ports.The second display is connected via displayport to the "DP out" port of the first display.
The first display is also used as a Dock to conect Keyboard, Mouse and ethernet via usb-c to the notebook.
When i conect the two display independently to the notebook (one via USB-c and the other with hdmi) they also work with WQHD resoulition.
Notebook Bios (1.9) and intel graphics driver are up to date.
Do you have any sugestions how i can get it work only via the usb-c port?
Can anybody say if the Vostro 7590 has HBR2 or HB3 Mode for the displayport via usb-c?
Thanks
jphughan
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January 19th, 2021 07:00
@H.T.Marley The Vostro 7590 is almost certainly DP 1.2/HBR2 since it uses 9th Gen CPUs, and the GPUs built into that CPU generation only support HBR2. And it is highly unlikely that the USB-C/TB3 port on that system is wired to the NVIDIA GPU instead of the Intel GPU. It's more likely that the Intel GPU controls the outputs and the NVIDIA GPU works only indirectly via NVIDIA Optimus.
Thunderbolt 3 can carry 8 lanes of DP 1.2/HBR2, but only when actually operating as Thunderbolt 3. If that display is just regular USB-C, then you have at most 4 lanes of HBR2. As you say, that's enough for dual QHD, but you only get 4 lanes over USB-C when you're carrying only video, or video and only USB 2.0. If the display is setting up the USB-C link to carry USB 3.x, that occupies 2 lanes, which means you only have 2 lanes for video. That is NOT enough for dual QHD when running HBR2. It is for HBR3, but again I don't think you have that here.
Some displays like Dell's U Series displays for a few years have a USB-C Prioritization feature allowing you to choose whether the display configures the USB-C link for 4 lanes of video and only USB 2.0, or 2 lanes of video and 2 lanes for USB 3.x. This is especially helpful with QHD displays, because with an HBR2 system, you can run single QHD and USB 3.x simultaneously. But if you want to daisy chain those displays, having this flexibility allows you to achieve that from an HBR2 system (if you're ok with USB 2.0) while still maintaining dual QHD and USB 3.x simultaneously on HBR3 systems that can handle that. But I don't know if your Philips display can be customized that way.
If that customization isn't available or USB 2.0 speeds aren't acceptable to you, then you'll have to use a USB-C to DP cable for video, which will force 4 lanes to be used over the system's USB-C output and thus allow the daisy chain, and then connect a separate USB cable to get a USB data path, which will be USB 3.0.
H.T.Marley
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January 20th, 2021 01:00
Thank you very much @jphughan
your description was very helpful and pointed me to the solution.
In my Philips 276B1 Display is an option wether the integrated USB Hub should operate at maximal level as a USB 3.2 Hub (default) or only as USB 2.0 hub.
After i changed the switch to USB 2.0 it was possible to connect both displays daisy chained with 2560 x 1400 at 60 Hz over only one USB-C cable connected to the notebook.
Also the USB-hub is functional but as expected only at USB 2.0 speed. As i only use it for keyboard and mouse this is fine for me. Also the gigabit-ethernet usb-adapter inside the display is shifted down from 1000 Mbit to 100 Mbit connection speed, but thats also fine for my personal setup because my internet connection is about the same speed.
Thank you.
jphughan
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January 20th, 2021 06:00
@H.T.Marley Excellent, and happy to help! Glad to hear your display offered that flexibility and that USB 2.0 isn't posing a bottleneck that's creating a practical problem for you.