T480 not recognizing external USB keyboard & mouse over USB 3

[MortySE]

Dear all,

I'm trying to get a T480 ready to give away as a gift. For this, I have purchased a Dell P2419HC monitor with USB-C. My plan was to used the Dell P2419HC as a "docking station", as it is designed to be used as. This works well with Dell laptops. The monitor is connected with a single USB-3 cable to the T480, with power delivery, USB and video running in one single cable.

It's fantastic ... except it doesn't work. The downstream USB 2 & 3 ports on the monitor don't work with the T480. The monitor ports seem to work, i.e. external harddisks spin up when attached, and similar. But the T480 doesn't recognize any USB devices that are attached on the monitors USB hub. When these same devices are attached directly to the T480's own ports, then everything works.

(The USB devices are just a basic Lenovo keyboard and Logitech mouse. And I cannot fully test the USB hub in the monitor, as I don't have any other USB 3 capable devices.)

It's a brand new Windows 10 install with all updates, and all Lenovo drivers loaded via Lenovo's System Update software.

After googling intensely I tried to:

• BIOS update to newest BIOS as of today
• Change all BIOS settings for Thunderbolt 3 to the most permissive -- as I read about similar issues du to Thunderbolt 3 security, and the physical port on the T480 is a dual mode Thunderbolt/USB 3 port.. Settings are now BIOS assist on, and and all Thunderbolt security off.

Still, everything attached to USB ports on the monitor isn't recognized by the T480. Power delivery and video through the USB-3 port works fine. USB ports on the T480 work fine too.

Any ideas, please? I'm desperate.

[dr_st]

Well, that's disappointing.

From checking the monitor's documentation I cannot find anything obvious that you could have missed.

Have you tried unplugging and replugging the cable? Power-cycling the monitor / the laptop?

At work I'm using a USB-C dock for my TP25/X1C, and intermittently I experience similar symptoms (power and video works, USB peripherals do not), which get resolved by one of the above.

Also, if possible, I'd try to locate a simple USB-C hub to check if that works with the T480.

[RealBlackStuff]

Don't know if it helps, but found this:

For the operating system to access any of the monitors USB downstream ports, the USB Type C to C cable must be connected from the PC USB Type-C port to the monitor USB Type-C port.

https://www.reddit.com/r/sysadmin/comme ... _monitors/

[MortySE]

@RealBlackStuff : Thank you very much. I have read that Reddit thread, and it seems to show this works Dell laptops and monitors.

@dr_st : Thank you for your help again. Yes, I have tried powercycling everything several times, reattaching cables, etc. No luck (so far).