Also on bugzilla.kernel.org:

https://bugzilla.kernel.org/show_bug.cgi?id=196297

Setup and brief environment:

    - Kernel 4.12.0 - vanilla, no patches

    - Dual-monitor setup

    - Monitor 1:

        - Dell U3011 30-inch 2560x1600 over DVI-I

        - Never has a problem

    - Monitor 2:

        - Seiki SE39UY04 (TV) over DisplayPort @3840x2160

        - Has a problem ONLY when monitor is SWITCHED OFF AND ON AGAIN

    - Graphics card:

        - GeForce GTX 750Ti 2GB GDDR5 128bit, Dual-Link DVI-I, HDMI, DP 1.2 Graphics Card

        - eVGA 02G-P4-3753-KR

        - eVGA link: http://www.evga.com/Products/Product.aspx?pn=02G-P4-3753-KR

    - Seiki monitor EDID:

        - The monitor has a bad EDID - see attached orig_edid.bin

        - I have a modified EDID file - see attached edid2.bin with ONLY the

            correct resolution

        - I use video=DP-1:3840x2160 drm_kms_helper.edid_firmware=DP-1:edid/edid2.bin

            to specify the exact resolution and use my custom EDID file

What works (perfectly):

    - Both monitors startup at full resolution

    - xorg starts up at full resolution on both monitors

    - Monitor 1 (Dell U3011) NEVER has any problem

    - While booting, nouveau finds and uses my custom EDID file

Problem:

    - When DPMS kicks in, the Dell U3011 monitor goes to sleep (normal) and

        the Seiki monitor shows 'No Signal' on the screen

    - About 15 mins after DPMS kicks in, the Seiki monitor switches off

    - The Seiki monitor has to be manually switched on with the power button

    - This behavior cannot be changed - no setting for this on the monitor

    - When I switch the Seiki monitor ON, the screen will be blank and

        'xrandr -q' shows it as disconnected

    - When I switch to a virtual console (using CTRL-ALT-F1), the following message appears

        on the console:

Jul  7 23:34:28 smaug kernel: [ 8340.750889] nouveau 0000:03:00.0: disp: outp 03:0006:0f42: link training failed

Jul  7 23:34:28 smaug kernel: [ 8340.750940] nouveau 0000:03:00.0: disp: outp 03:0006:0f42: link not trained before attach

    - This message appears ONLY when I switch to the virtual console, and NOT until then

    - When the monitor is switched on, the attached kernel trace appears in the kernel log

    - After switching to the virtual console and back to X, the monitor will show

        a SERIES of garbled screens (probably bad timings, but I am not sure), each

        lasting about 10-15 secs. After a few MINUTES (perhaps 2-3 minutes),

        the Seiki monitor will be restored back to full resolution

    - As the monitor is restored to full resolution, the following message will

        appear in the kernel log:

Jul  7 23:37:44 smaug kernel: [ 8537.487664] [drm] Got external EDID base block and 1 extension from "edid/edid2.bin" for connector "DP-1"

    - The problem only happens if the Seiki monitor is in the OFF state for QUITE A LONG TIME

    - E.g., if I turn it back on within 5 mins, the problem does not occur

Problem wasn't happening until about 4-5 months ago (when I was using an older kernel version).

I have gone back to 4.11, but it still happens. Must be a versionolder than that. Unfortunately, I do not remember which version worked, but was a 4.x version.