Arch Linux

aftsak

Member

Registered: 2014-08-04

Posts: 10

USB-C screen not detected reliably

Hi Arch Linux Community!
I have been fighting with this issue for quite some time now. Time to ask for some help :-)

I connect my laptop to my USB-C screens using a single cable and daisy chaining. It feeds power to the laptop and I also have Logitech USB receivers connected to the screen USB hub.

It doesn't work reliably and I was never able to find what / why. The screens are not always detected (i.e. xrandr does not report any connected screen). When the screen doesn't work, USB devices like mouse and keyboard are not detected either. What I have tried so far:

- Start the laptop and login before plugging the USB-C screen: sometimes it works, sometimes not
- Plug the USB-C screen before starting the laptop: sometimes it works, sometimes not
- Unplug the screen, wait 1min, plug again: sometimes it works, sometimes not
- I usually get it working after many trials and errors, but it usually requires many reboots / attempts
- I have been updating my Kernel through several releases and it never improved.
- Once it fails, it feels like my USB-C bus is "blocked" until the next reboot. I don't see anything happening in dmesg output when connecting / disconnecting the screens, while I should see all USB devices being detected. But power is still flowing.
- Sometimes the screens are detected by xrandr, are enabled in the display manager, but no image is shown
- I am using the screens with a Mac perfectly fine (no daisy chain, using 2 USB-C cables)
- I have changed the USB-C cable 3 times with different brands, now using a Apple Thunderbolt cable which should be high quality....

When I look at the logs, I sometimes see this entry. But I have had the screen working even with it in the logs:

[   10.137208] i915 0000:00:02.0: [drm] *ERROR* Link Training Unsuccessful
[   10.663675] ucsi_acpi USBC000:00: PPM init failed (-110)
[   10.764887] i915 0000:00:02.0: [drm] *ERROR* Link Training Unsuccessful
[  106.952918] usb 3-2: USB disconnect, device number 2

My Hardware:
Laptop: Yoga Slim 7 with Intel i5-1135G7
Screen: 2x Lenovo ThinkVision p27h-10 with USB-C cable

I am kind of stuck and don't how how to troubleshoot further.
Any idea ?
Thanks for your help

Last edited by aftsak (2023-09-21 05:11:42)

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,995

Re: USB-C screen not detected reliably

Lenovo ThinkVision p27h-10 specs :

Connectivity
2 x HDMI 1.4
1 x USB 3.1 Type-C (DP1.2 Alt Mode)  1 x DP 1.2
1 x DP-Out
4 x USB 3.0 with 1 x BC1.2
1 x Audio Out (3.5mm）

Are you using the DP-Out port to daisychain both monitors ?

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

aftsak

Member

Registered: 2014-08-04

Posts: 10

Re: USB-C screen not detected reliably

Are you using the DP-Out port to daisychain both monitors ?

Correct, the setup looks like this

|--------|       |------------------|     |------------------|
| Laptop |       |    Monitor 1     |     |    Monitor 2     |
|  USB-C |       | USB-C    DP-Out  |     |      DP-In       |
     v               ^        v                    ^
     |---------------|        |--------------------|
        usb-c cable                  DP cable

The USB-C connection is used for Display, Power and USB devices (the monitor has a USB hub)

Rosemary

Member

Registered: 2023-07-18

Posts: 2

Re: USB-C screen not detected reliably

Does it work on mac if you are daisy chaining them? Also I found this article that sounds useful https://askubuntu.com/questions/1331399 … -via-usb-c .

aftsak

Member

Registered: 2014-08-04

Posts: 10

Re: USB-C screen not detected reliably

Daisy chaining does work sometimes with my ArchLinux laptop, maybe 50% of the time. Except just being lucky or getting the timing right on when to plug the screen (I have tried before, during, after startup, nothing works reliably), I haven't been able to identify a difference when it works or not. Nothing stands out in dmesg or other logs. But the screen config and cable setup should be right.

Does it work on mac if you are daisy chaining them?

My Mac does not seem to support daisy chaining with this monitor setup, it never worked. I found contradictory information in Apple forum if MST is actually supported by MacOS or not... Some says only Thunderbolt screens (crazy expensive) will support daisy chaining.

I am looking for any hints on which logs I should be looking at... Thanks

Last edited by aftsak (2023-07-19 07:24:19)

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,995

Re: USB-C screen not detected reliably

Does the daisychaining work reliably if the laptop gets power from a wallcontact directly instead of through the usb-c  cable ?

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

aftsak

Member

Registered: 2014-08-04

Posts: 10

Re: USB-C screen not detected reliably

I haven't tested this so far but will give it a shot, thanks!
My laptop only allows charging over USB-C, and I cannot disable the USB-C charging from my screen.
I will try plugging a USB-C power charger in addition to the USB-C screens for the next couple of days. If you had something else in mind or if you know a way to prevent/disable charging over the screen USB-C cable, please let me know.

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,995

Re: USB-C screen not detected reliably

Some people with similar issues found it helped to 'terminate' the daisychain by disabling MST on the screen at the end of the chain.

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

aftsak

Member

Registered: 2014-08-04

Posts: 10

Re: USB-C screen not detected reliably

Some people with similar issues found it helped to 'terminate' the daisychain by disabling MST on the screen at the end of the chain.

After one month of testing, I never had a single issue with MST disabled on the second screen. I started getting issues again after re-enabling MST.
Disabling MST on the terminating screen seems to solve the issue for me!

Thank you so much, you just put a stop to two years of troubles and frustration!

aftsak

Member

Registered: 2014-08-04

Posts: 10

Re: USB-C screen not detected reliably

I guess I celebrated too soon. I am still experiencing this issue from time to time. It is definitely less frequent, but still present.
Usually unplugging, waiting 30sec, plugging my USB-C cable into the other port fixes the issue. Sometimes I have to try multiple times.
Sometimes the only fix is to reboot.
Not sure what could be happening.