Just found a quick way for disabling internal display on i915.
Using command modinfo i915, there will be an options called panel_ignore_lid.
According its description, panel_ignore_lid:Override lid status (0=autodetect [default], 1=lid open, -1=lid closed) (int).
So create a new file under /etc/modprobe.d name it i915.conf
Adding following:
options i915 panel_ignore_lid=-1
You are done! (Don’t forget to reboot)