Monitor powers off and on after every login

Hello, all-

I’m running a dual-boot system with openSuse and Windows 10, Dell I3847 with integrated Intel graphics.

System works great, SDDM fires up just fine, but when I log in to Plasma (6), the splash screen shows, desktop opens, then the monitor powers off, and back on.

It’s a complete power off, as the Samsung logo displays on power up, then the source banner (HDMI indicator) displays at the top (monitor function). After that, everyting works normally. If I log out, and log in again, it does the same thing.

This happens in both Wayland and X11. Logging on with Ice or Xfce does not produce the issue. I don’t have Gnome installed.

This is weird and sounds to me like a problem with the screen that reboots when changing modes or sth.

Can you see if setting DPMS off and on triggers this “reboot”?

Using kscreen-doctor --dpms off; sleep 5; kscreen-doctor --dpms on

No, not the same. That caused the screen to go black, but the monitor did not power off and on.

Can you try disabling the use of libddcutil in the PowerDevil service as described in this README file, with POWERDEVIL_NO_DDCUTIL=1 and service restart? I wonder if your monitor chokes on any of the DDC/CI commands sent during initialization.

(To be clear, PowerDevil doesn’t try to set anything during initialization. It mostly just looks for connected monitors and asks for their current brightness.)

ISSUE SOLVED! I had the POWERDEVIL_NO_DDCUTIL=1
line in the file, but noobiously left out “Environment=”. Duh.

Full line should read Environment="POWERDEVIL_NO_DDCUTIL=1"

Thank you, @jpetso and @guss77!

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So then, it’s an issue with libddcutil. Would you like to investigate it any further? I’d be curious if listing monitors and/or retrieving brightness values will cause the same issue also if you use the ddcutil command-line tool.

Getting it fixed “properly” will likely involve a good bit of back and forth, but could return your brightness controls in Plasma and help other users that might be experiencing the same issue.

I don’t usually use the software brightness controls, but I’d be happy to help. I should mention that the monitor is a Samsung un48j5200afxza Full HD TV (1920x1080), made in 2015.

ddcutil capabilities reports “Display not found”. It then powers the monitor off and on.

This seems to hit the nail on the head - scanning for capabilities crashes the monitor.

I believe that if you can run sudo ddcutil --trace all capabilities and dump here the output - that would be useful for understanding the problem better.

I see, thanks for checking. Does this also happen if you do a simple ddcutil detect?

Given this, I wonder if it would be better to open a new issue at Issues · rockowitz/ddcutil · GitHub (perhaps after quick search for possible duplicates first) as that’s where any fix would have to go. And also because the ddcutil maintainer has a way better understanding of all the things that could go wrong.

Could you please try with different cables? I had various issues in the past because of bad DP cables.

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I ran ddcutil --trace all capabilities and it dumped 55,800 characters, too many to put in a reply. I have it in a plain text file, though, can I send it to you somewhere?

ddcutil detect gives the following, then the monitor cycles power (apparently)

Invalid display I2C bus: /dev/i2c-3 DRM connector: card1-HDMI-A-1 EDID synopsis: Mfg id: SAM - Samsung Electric Company Model: SAMSUNG Product code: 3129 (0x0c39) Serial number: Binary serial number: 0 (0x00000000) Manufacture year: 2014, Week: 46 DDC communication failed. (getvcp of feature x10 returned Error_Info[ENXIO in ddc_write_read_with_retry, causes: ENXIO])

That’s a possibility, the cable is from 2014, as well. I’ll try to scrounge one up.