After installing Ubuntu 19.10 on my Lenovo X1C (gen 7), I tried to hook it up via USB-C/Thunderbolt to my LG monitor. However, the display (and USB connection) flickers or blinks, i.e. the screen goes black for one to five seconds, the power led next to the USB-C port in the computer goes off, and no input from the external keyboard or mouse (hooked up via USB-C and the monitor's USB hub) is registered. Reducing resolution doesn't seem to make any difference, and using the HDMI port works stably.
From dmesg
, I thought the following warnings which seemed to occur when the blinking happens, and which seemed relevant:
[509746.116260] WARNING: CPU: 0 PID: 12232 at drivers/usb/typec/class.c:302 typec_altmode_update_active.cold+0xc/0x13 [typec]
[509746.935963] WARNING: CPU: 0 PID: 12232 at kernel/module.c:1137 module_put.part.0.cold+0xc/0x13
...but according to my logs, these went away about one week ago, and I have definitely seen blinking after that.
Let me know if it would be useful to paste in (or otherwise make available) the full log or warning output.
Update: the following seems to describe the same problem. Here it is associated with the Thunderbolt dock (and using Windows), while I use a direct USB-C output and (obviously) Ubuntu. Two people report this only happening when simultaneously charging, which describes my situation (I don't have a non-charging USB-C display)
Workaround: The flickering only seems to occur if I run the two displays (the internal LCD and the Thunderbolt-connected monitor) as separate screens, somehow. If I start X with both monitors connected, the external gets configured with the same (HD) resolution as the interal display - but it seems stable. If I configure it manually (xrandr --output DP-1 --left-of eDP-1
) it is unstable. If I reconfigure it (xrandr --output DP-1 --same-as eDP-1
) it is still unstable. Changing resolution of the extneral display (xrandr --output DP-1 --mode 3840x2160
) doesn't seem to affect stabilty, it's still solid after a few hours.