@Kai-Heng

Concerning your question:
v4.12-rc1 with NOMODESET -> Successfully logged in.
v4.12-rc2 with NOMODESET -> Successfully logged in.
v4.12-rc5 without NOMODESET-> Successfully logged in.
Can I say that -rc2 has freeze but -rc5 doesn't freeze?

I would say that neither of those two kernels freeze. However they behave differently depending whether NOMODESET is configured. For example, -rc5 shows a wired behaviour when NOMODESET is used. This is explained further below.

In the light of your question I have run the tests again, but this time without modifying the kernel parameters so they are the ones that come with it by default. (i.e. only "quiet splash").

Short answer (vanilla - no additional kernel parameters set):
v4.12-rc1 -> Successfully logged in but login screen on built in monitor.
v4.12-rc2 -> Successfully logged in but login screen on built in monitor.
v4.12-rc5 -> Successfully logged in as I would expect it to work.
4.10.0-35-generic -> No login possible due to login screen never being shown.


Long answer:
v4.12-rc1 -> Same as v4.12-rc2
v4.12-rc2 -> Booting the laptop with lid closed. It does not show the login screen on the external monitor but found the login screen on the built in monitor after opening the lid. I then successfully logged in by using the external keyboard. After the login the built in monitor got disabled (no user intervention from my side) while the laptop lid was still open. The external monitor is active and displays the desktop with correct resolution. The external keyboard continued to be working after login.
v4.12-rc5 -> Successfully logged in. It correctly used the external monitor only and the keyboard continued to work after login.
4.10.0-35-generic -> The login screen is never displayed. I can see the progress icon circling endlessly. Note, the icon itself continuous to move all the time but nothing else beyond that happens. Furthermore, both screens are active and show the progress icon.


Furthermore, I have then tested v4.12-rc5 with NOMODESET again, with flowing outcome.

v4.12-rc5 with NOMODESET -> Booting laptop with lid closed. The login screen gets displayed on the external screen correctly. I then logged in by using the external keyboard, which was then followed by a black screen (i.e. monitor reported no signal) on the external monitor (note, the laptop was still closed). The laptop does not appear to react to any keystrokes. As of my testing, this black screen would remain there until the laptop lid was opened once. At least in two out of three tests this was the case, whereas with one test I was not able to get to the desktop at all. I have tested it three times by waiting differently long periods and it appears that opening the laptop lid causes the external screen to eventually show the desktop (after 20 to 30 seconds) in two of the three test cases. Note, the built in laptop screen remains black all the way. Furthermore, after the login, the external keyboard stopped working. This might explain that the laptop did not react to my keystrokes since the laptop lid was closed during this period and thus the built in keyboard was not available to me. Another observation is, which is probably i915 related too, that the external keyboard only worked after the USB dongle was removed and re-connected to the docking station.