My external monitor (dell) is not detected on my Asus Laptop if I switch it on only after I booted the laptop.
The case similar to How to make linux detect/re-probe monitors with intel i915 driver?, except that in my case, once it is known to the laptop, I can unplug and plug it in again and get it detected.
Only when the external monitor is off during boot, I cannot get detected.
The solution with
echo detect > /sys/class/drm/card0-DP-1/status, does not work, because the relevant directory would be
card0-DP-2, which simply does not exist after booting while the monitor is off.
Other solutions like CTRL-ALT-F1 and back similarly don’t work.
Unplugging the cable and plugging in again has no effect either. It feels a bit as if the whole displayport plug of the laptop is simply off completely.
Strange finding: if the displayport cable is not connected during boot, then the monitor is detected when I switch it on and connect the cable after booting (:-( So it seems the combination “cable connected/monitor off during boot” is interpreted as “don’t bother with this hardware anymore”.
Is there some command telling the system to reconsider the question whether something is connected to the display port?