Monitor powers off and on after every login

Help
1

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.

2

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

3

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

4

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.)

5

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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6

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.

7

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.

8

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

9

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.

10

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.

11

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

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12

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?

13

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])

14

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

15

For reference, there is 494522 – Powerdevil causes Samsung Odyssey G5 to go on/off repeatedly forever with DDC support enabled which seems very related.

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