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bai4Iej2need

Member

From: Ortenau

Registered: 2021-04-25

Posts: 158  

with dual monitor from display port over HDMI to 2nd Monitor

Hardware:
Lenovo-r500, with a local display
1 DP to HDMI adapter
1 HDMI Cable of 6 meters
remote is a TV set with 3 HDMI inputs

Xorg -version
X.Org X Server 1.21.1.7
X Protocol Version 11, Revision 0
Current Operating System: Linux lenovo-r500 6.1.0-45-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.170-1 (2026-04-30) x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-6.1.0-45-amd64 root=UUID=2da904de-743c-4e19-ac3f-5ec79cf96870 ro quiet noapic lsm=none
xorg-server 2:21.1.7-3+deb12u11devuan1 (https://www.devuan.org/os/community)
Current version of pixman: 0.42.2

when running
echo detect > /sys/class/drm/card0-DP-1/status

then the kernel reports the monitor as connected. when opening a console, the console is mirrored on the TV monitor.
However the console disappears after a few 10 or 20 seconds.
The kernel reports then disconnected.
cat /sys/class/drm/*/status
disconnected
disconnected
disconnected
connected
disconnected

Before XRandr is then able to detect the TV Monitor, but not able to create a dual display setting.
How to make the kernel keep the detected used displayport ?

---

The devil, you know, is better than the angel, you don't know. by a British Citizen, I don't know too good.
One generation abandons the enterprises of another like stranded vessels. By Henry David Thoreau, WALDEN, Economy. Line 236 (Gutenberg text Version)
broken by design :
https://bugs.debian.org/cgi-bin/bugrepo … bug=958390

bai4Iej2need

Member

From: Ortenau

Registered: 2021-04-25

Posts: 158  

Re: with dual monitor from display port over HDMI to 2nd Monitor

Now I have used the actual backports kernel .
uname -a : Linux lenovo-r500 6.12.85+deb12-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.85-1~bpo12+1 (2026-04-30) x86_64 GNU/Linux
Now xrandr is able to establish a dual monitor session, how ever it also stops aftersome delay. (few minutes).
Obviously X stops sending a signal through DP-1. The TV complains "No signal"

---

The devil, you know, is better than the angel, you don't know. by a British Citizen, I don't know too good.
One generation abandons the enterprises of another like stranded vessels. By Henry David Thoreau, WALDEN, Economy. Line 236 (Gutenberg text Version)
broken by design :
https://bugs.debian.org/cgi-bin/bugrepo … bug=958390

KindlyDoRight

Member

Registered: 2026-10-05

Posts: 28  

Re: with dual monitor from display port over HDMI to 2nd Monitor

In recent months, I experienced similar "disconnect" (and flickering) symptoms with a triple monitor setup on KDE Plasma on X11 (a setup which had been completely stable for several years -- from Kubuntu 20.04, to Debian 11, 12, and 13; on a GTX 1060 and RTX 4080 -- yeah, stable with Nvidia).
So, I did try xrandr bootup settings, changing resolutions (trouble-shooting), etc.  I was seriously considering replacing the affected monitor. (my heart couldn't bear to consider it might be the graphics card $$$ 😟)

But (stubbornly, after a couple of weeks), I went ahead and swapped out my high quality, *premium* 18' (5.5 meter) flat HDMI cable with a 12' cable I had on-hand.
And... that resolved my issue completely.

My premium (read, expensive) 18' flat HDMI cable was apparently experiencing an expansion-gap disconnect.
A temporary "gap" caused by heat expansion from the warmth of the graphics card or monitor (likely, the monitor due to its dormant sleep mode overnight, and constant use during the day).

So, I bought a brand new HDMI cable (for the length I actually needed), and it's been completely stable.

I suppose (I wildly conjecture) that, in trouble-shooting, perhaps turning the cable around will provide a little more useful life out of such a cable.  What I mean is, swapping the cable ends: plug the monitor end of the cable into the GPU, and vice-versa.
-- Because, sometimes, you got to have a temporary solution to get you by.

TLDR - I replaced an intermittently bad HDMI cable.

Last edited by KindlyDoRight (2026-10-06 10:25:19)

EDX-0

Member

From: Guatemala

Registered: 2020-12-12

Posts: 265  

Re: with dual monitor from display port over HDMI to 2nd Monitor

yeh fun how even displays and display cables may require cooling off, everyone obsesses over cpu and gpu temps gladly forgetting that other components can also experience issues from thermal cycles, thermal shifts and everyone's favourite, thermal expansion.