L5 dock - flickering convergence display

I’m troubleshooting an L5 dock and monitor. Particularly the display/convergence part. The nameless dock works fine regarding keyboard, mouse, power and ethernet. But the HDMI causes the display/convergence (and therefore the display options) to flicker/flash. The monitor is identified but it only lasts for about 5-8 seconds when the monitor disappears (options revert to basic L5 and the icon on the top disappears). This repeats for some time until L5 gives up. I’ve tested several monitors, HDMI cables, dock connection, with and without other peripherals (keyboard, mouse and power keep working).

Since the monitor(s: HP, Samsung, LG) is identified and correct options given (although there is no time to set the up and apply them before another “disconnection cycle”), my current working theory is that there is something wonky in system or settings. Has anyone come across something similar? Any idea what the cause could be? Tips for getting relevant data for troubleshooting?

Is that a known? Usually if you get an initial picture that goes away the monitor gives up because the signal is outside the spec.

I’d check in that order

  • The kernel lock. If the DP driver throws it’s arms in the air it’s likely fixable on the sw side
  • the USB-C cable from the phone to the dock (it’s usually fixed to the dock). Try both orientations. This is the most sensitive point (the fact the e.g. a keyboard works doesn’t say much as USB has way less bw and signal quality demands than DP). There’s lots of bad cables around. I have one device that works fine if you make sure to not touch the cable
  • The HDMI cable from the display to the phone
  • The DP firmware version (different firmware versions send slightly different DP parameters). See the bottom of this page: https://source.puri.sm/Librem5/firmware-tps6598x-nonfree/-/blob/master/dp-alt-mode-adapters.org

See Docked mode · Wiki · Librem5 / Librem 5 Community Wiki · GitLab for what else to check. If all else fails it might be the phone hw (if no other docks work either) from your description it might be an outdated DP firmware though.


Based on the observation that L5 screen goes dark after a while (not timed with screen saver) and the external monitor needs to be disconnected from the dock to get it back.

I’ll try the suggestions, thanks.

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It’s very likely not the L5 userspace side giving up here then. One other thing to check is if the picked mode (wlr-randr) matches the mode other devices pick when attached to the same monitor.


I couldn’t get a handle on the kernel lock - not an area I’m familiar with. Some sources even suggested current Debian based don’t have that. Not sure what to do about it or how to check it.
All three firmware versions are the latest, matching what’s at the bottom of the page.
HDMI cable tested and changed but no change.
USB-C from dock is fixed and orientation… seems to have changed something. At first, during several attempts, the situation got worse, as the screens went totally dark in some cases. The L5 actually both logged out and closed apps, as well as, rebooted, when removing the dock. But after one reboot - for some unknown reason - the connection was stable… and I haven taken the cable out since. This doesn’t seem to be physical connection related, because movement doesn’t seem to have any effect, which is strange (a random connection issue with the cable would be simple and understandable).

But, something new: even though the mouse does move between both displays, the settings window doesn’t respond - I can’t move it or change display settings, no reaction on the window on either display (settings window open half on both). Testing with terminal window, that on the other hand works well.
Edit to add: the settings window is a headache. It’s behaving erratically and it seems part of the screen is shared by the L5 and the monitor, even though according to the settings window (drag displays) they don’t overlap.
Edit to add 2: this seems to have been caused by Mobile-Settings app, where I had compositor set on Settings. Seems to have been solved by disabling that.

So, currently, halfway solved: secondary display is alive, no flickering - now just need to get the settings right (and hope that when I eventually remove the dock I can get it to work again in less than three days).

Other notes: Mobile-Settings Convergence does not see any dock. Not sure if that matters, though.

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Nope, spoke too soon. When L5 blanked screen the other monitor reset it’s display settings and the settings window became trapped between two displays again. No reaction. Can’t even kill it because it doesn’t show up in Usage.
The settings window is somehow different…? Other apps don’t get locked like this.

L5 rebooted again. And waking up with the dock attached is painful. Several times L5 has gone blanc and logged out. The earlier flickering behavior has returned even though the dock and phone have not been touched. Only way out is to reboot, which is a bit odd - why is the settings window the one that’s so fragile?

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