Bugzilla – Bug 901887
[Intel, HSW, DP] Lenovo t440s / Intel 4400: External display non-functional
Last modified: 2021-08-03 08:49:13 UTC
Created attachment 610633 [details]
On the same system where I experienced bug 899501, I've updated the system to a later Factory build and can now no longer activate my external display at all.
Though xrandr reports:
Screen 0: minimum 8 x 8, current 1920 x 1200, maximum 32767 x 32767
eDP1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 309mm x 175mm
800x600 60.32 56.25
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
DP4 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 546mm x 352mm
DP5 disconnected (normal left inverted right x axis y axis)
The output on DP4 is black, and the monitor does not detect a signal.
I had played with xrandr --off / --auto for a while for that output (turning the monitor's power on/off etc as well), and then eventually gave up and turned the display off.
After ~2h hours, I decided to give it another try, turned on the monitor, and ran xrandr --output DP4 --auto again. (A sequence I had done multiple times before). Lo and behold, this time, the monitor came online fine and is now displaying.
I don't know why, and I don't really trust the result ;-) It was also not reproducible, there's nothing new in the logs from either X or in dmesg. I can't tell what is different now.
Intel HSW PCI ID: 0x0a16.
Lars, is this still an issue for you?
If so, please set the kernel boot option drm.debug=0x6 and provide the dmesg output from failed attempts to light up the external monitor.
One more question - when you try to light up the external monitor - does it come put of DPMS (ie does the backlight come on or does the power LED change from amber to green)?
No feedback for almost 2 months now. Closing.