No HDMI output unless connected at boot time

I installed OpenWrt on a x86_64 machine. However, if a HDMI cable (and a monitor via it) is not connected at boot time, video is not output even if the HDMI cable is connected during running OpenWrt. If the HDMI cable is connected at boot time, the video will be output, and even after unplugging and plugging it again, the video will be output again.

I don't usually want to connect an HDMI cable to the router, and only want to connect it during maintenance, such as when ssh is unavailable, so this situation is not good for me.

Is there any way to fix this?

This situation occurs under the following conditions:

  • Intel Celeron N5105 (Jasper Lake) without a discrete GPU
  • OpenWrt 22.03.3 and OpenWrt 21.02.5

Also, since this problem does not occur on other OS (Ubuntu), I do not think that hardware limitations are the cause.

Try adding nomodeset to the Linux params.

Thanks for the reply.

Adding nomodeset means changing /boot/grub/grub.cfg as follows, right?

- linux /boot/vmlinuz root=PARTUUID=<uuid> rootwait nomodeset console=tty0 console=ttyS0,115200n8 noinitrd
+ linux /boot/vmlinuz root=PARTUUID=<uuid> rootwait console=tty0 console=ttyS0,115200n8 noinitrd

I tried that and rebooted, but it still doesn't seem to work.


There's probably some kernel option to force output even if no screen is detected, of not , get something like, but cheaper.

There's probably some kernel option to force output even if no screen is detected

This gave me a hint, and after much searching, I discovered that what I needed was this option i915.force_probe.


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