[Solved] Monitors won't turn on during boot or restart, but will turn on coming out of sleep mode. (...and other solved issues)
Thinkpad P1 Gen 2, Windows 10 Pro, i7 processor, internal GPU nVidia T2000, integrated Intel UHD 630
eGPU Sonnet Breakaway 350W, MSI GTX 1070 Gaming X 8G. Connected via Thunderbolt 3.
Machine up to date on all Lenovo and windows drivers (except windows feature upgrade 2004). nVidia 446.14
Some background information. I have been using the eGPU with a Thinkpad T480 (integrated graphics only) for the past 2 years and it has worked perfectly. The P1 not so much.
When I first connected the P1 to the eGPU and was using the external monitors there was serious lag and stutter on the external monitors. I found a lot of information about this and appears to be a known problem with no permanent fix. Best I could do was disable the integrated graphics in device manager and that solved the stuttering, however sleep mode disappeared from P1. Not good. Solved that problem by changing BIOS to use discreet graphics only (no Hybrid). Stutter gone and sleep mode is back.
Now the current problem. The external monitors will not go active on a reboot or starting up. I am forced to sign in on the P1 screen, once I do that the external monitors will go active. The eGPU has power and is running the whole time, but the monitors show no signal until I logon to Windows on the laptop screen. Once I do the screens flicker and turn on. Sleep mode works fine, monitors come on and I can logon to Windows on an external monitor with or without the lid open on laptop. I have Windows configured to use one of the external monitors as my main display and the desktop is extended to it. Any ideas? As I said it worked perfect on the Lenovo T480.
I figured it out and solved all my issues. It was Thunderbolt Kernel DMA protection in BIOS. I disabled that and I can now use my intel UHD 630 gpu and no stuttering, I have sleep mode and I can reboot my P1 and logon to windows from external display.
Warning: I understand that my PC is vulnerable to physical hands-on the unit attacks (thunderspy). I am okay with that risk because my unit rarely leaves my house and I dont work in national security.