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Last reply by 04-04-2021 Solved
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4k@60Hz over USB-C is possible on Dell 7410?

Hi,

I'm trying to understand if it is possible to get 4k@60Hz working via usb-c docking station on Dell Latitude 7410. When I connect 4k@60Hz display directly to notebook HDMI port, it works as expected. If I connect the same display to dock via DisplayPort or HDMI, and the doc is connected via usb-c, I get only 4k@30Hz

Spec here https://www.dell.com/en-us/work/shop/2-in-1-laptops-tablets/new-latitude-7410-business-laptop-or-2-i... states for usb-c ports:

Thunderbolt™3 with Power Delivery and DisplayPort (USB Type-C™)

Explanation here https://www.dell.com/support/kbdoc/en-us/000141309/guide-to-thunderbolt-3  says

Thunderbolt™ 3 is a superset solution which includes USB 3.1 (10Gbps), and adds 40Gbps Thunderbolt™ and *DisplayPort™ 1.2* from a single USB Type-C port.

The doc spec https://www.lenovo.com/us/en/accessories-and-monitors/docking/universal-cable-docks-usb/TP-USB-C-DOC... says

Dock has the ability to support DisplayPort™ 1.4 and HDMI™ 2.0 for max 2 x 4K @ 60 Hz displays, but the real video output would depend on the system's output.

So the question is: is this Dell 7410 limitation on usb-c port (because it outputs only DP 1.2 to dock), or this is incompatibility with the dock, and if I take some other dock model (with Thunderbolt?), I should be able to get 4k@60Hz from that usb-c port?

One more confusing thing is here https://www.dell.com/support/manuals/en-us/latitude-14-7410-2-in-1-laptop/lati_7410_ss/left-view

USB 3.2 Gen 2 Type-C port with DisplayPort (alt mode), Thunderbolt 3.0 with Power Delivery(PD) 

It states that port is actually USB 3.2 Gen 2, not USB 3.1 (10Gbps), which should be enough for 4k@60Hz

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7 Thorium

@Pxx64  The USB 3.x generation standard support has nothing to do with display bandwidth. A connection to a USB-C dock would involve sending native DisplayPort over certain pins and USB data over other pins, and systems can support different DisplayPort revisions and different USB 3.x data. Those two have no effect on each other. Yes, the Latitude 7410 only supports DisplayPort 1.2/HBR2 over USB-C. That is enough for 4K 60 Hz, but only when all four high speed lanes in the USB-C connector are allocated to video. When you use a docking station, it configures the link to support both video and USB 3.x. Running USB 3.x requires two lanes, which leaves only two lanes for video, meaning that your video bandwidth gets cut in half. Running 4K 60 Hz and USB 3.x simultaneously requires DisplayPort 1.4/HBR3, since its higher bandwidth means that even a half-bandwidth link will be sufficient for 4K 60 Hz.

The other option would be a Thunderbolt 3 dock, which would allow dual 4K 60 Hz and USB 3.x simultaneously even from your HBR2 system.

I wrote an explainer post about the various operating modes of USB-C and Thunderbolt, with particular focus on the impact on display setups, over here if you’re curious.


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7 Thorium

@Pxx64  The USB 3.x generation standard support has nothing to do with display bandwidth. A connection to a USB-C dock would involve sending native DisplayPort over certain pins and USB data over other pins, and systems can support different DisplayPort revisions and different USB 3.x data. Those two have no effect on each other. Yes, the Latitude 7410 only supports DisplayPort 1.2/HBR2 over USB-C. That is enough for 4K 60 Hz, but only when all four high speed lanes in the USB-C connector are allocated to video. When you use a docking station, it configures the link to support both video and USB 3.x. Running USB 3.x requires two lanes, which leaves only two lanes for video, meaning that your video bandwidth gets cut in half. Running 4K 60 Hz and USB 3.x simultaneously requires DisplayPort 1.4/HBR3, since its higher bandwidth means that even a half-bandwidth link will be sufficient for 4K 60 Hz.

The other option would be a Thunderbolt 3 dock, which would allow dual 4K 60 Hz and USB 3.x simultaneously even from your HBR2 system.

I wrote an explainer post about the various operating modes of USB-C and Thunderbolt, with particular focus on the impact on display setups, over here if you’re curious.


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@Pxx64  EDIT: Removed


Hi @jphughan,

Thank you, now all things became clear to me :). As I didn't dig deep, I assumed that DP traffic is incapsulated in USB (among others), but if it is hardware split based on available lines, then it is understandable why 4K 60 Hz is not available. Will try to convince my manager that I need a TB3 dock instead of corporate standard USB-C dock

@Pxx64  Happy to help. And sorry about the confusion with my second post saying that you had linked a Thunderbolt dock. Somehow I read the product page too quickly. Lenovo has a ThinkPad USB-C Dock Gen 2 and a ThinkPad Thunderbolt 3 Dock Gen 2. They look almost identical in product photos. But you’d need something like the latter. Although Dell’s equivalent would be the WD19TBS. If you’re only using a Dell system rather than swapping between a Dell and Lenovo system, you might want to run a Dell dock. If nothing else, it will give you the ability to use the dock’s Power button to control the system. There’s no industry standard for an external Power button, so that only works when the vendors of the dock and system match.


Well, as we are buying Lenovo docks at scale for Dell/Lenovo/Macs, I assume it would be easier to get a TB3 from Lenovo than trying to find Dell model here (even if it will be approved). And the power button is not an issue here, as the dock will be laying over the monitors anyway, so no difference in going to the notebook, or dock

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