Computer: Thinkpad T460p GPU: NVIDIA GeForce 940MX Integrated Video: Intel HD Graphics 530 OS: Windows 10, 1709 (Fall Creator Update) Cable: Full size Display Port
When Windows tries to put the displays to sleep after X minutes, the P2415Q will show "Entering Power Save Mode", go to sleep, then turn back on in ~30 seconds, at which point it repeats the loop again.
This happens both with the laptop docked (using full size DP to DP) and un-docked (using laptop mDP to P2415Q full size DP).
It does not seem to happen when hooked up to a MacBook Pro 15" Retina (~2015), using TB to DP.
I have reinstalled Windows 10 without any Lenovo drivers, and the same behavior occurs.
Seems like the same issue could be happening here, with a Surface Pro 4.
SP4 mDP out, P2415Q DP in, Windows 10 = PSM issue
ThinkPad T460 docked DP out, P2415Q DP in, Windows 10 = PSM issue
ThinkPad T460 un-docked mDP out, P2415Q DP in, Windows 10 = PSM issue
MBP TB out, P2415Q DP in, Apple OS = No PSM issue
From a P2415Q hardware perspective, you have shown that the fault is not with the P2415Q DP in port.
In all of the scenarios where the PSM issue happens, the constant is Windows 10. The fact that the MBP does not have this issue because of a different OS points to Windows 10 or the GPU drivers in Windows 10 as being the culprit.
It appears that the MBP, when entering its PSM, is still "initiating" the handshake from its GPU to the P2415Q. So no PSM message.
Conversely, the other systems with Windows 10, the handshake from the GPU to the P2415Q is actually being stopped and not restarted, thus the PSM messaging.