I have the latest Intel NUC, NUC6i7KYK (specs here), running close to stock Ubuntu 16.04. Its monitor is hooked up via HDMI.
When it wakes up from suspend (S3), it never wakes up the display. The system is up and responsive (I can ssh in), but the display stays off, with no signal. No amount of turning off/on the monitor or unplugging the HDMI cable will restore it.
I tried some of the steps from this guide and found the exact same issue when booted into "runlevel 3", which boots into a console instead of X. (I believe in this case the intel video drivers are still in effect, since the console it boots into is clearly in graphics mode.)
I have not tried hooking up a monitor via DisplayPort because I don't have a capable monitor, so I'm not sure if it's specific to HDMI output or not.
How can I diagnose and fix this issue? Most of the guides I can find are seemingly out of date (e.g. from the article I linked, I can't find the
intel_gpu_dump tools, nor does
/proc/acpi/event exist, etc.) or don't go into enough detail (e.g. I was looking at section 3.2.1 of this page, but I have no idea what it means to "set
I had it dump
dmesg after waking up. The full output that came after suspending is here, perhaps these two lines might be a clue, if they mean anything to anyone:
[ 158.639355] [drm:intel_dp_link_training_clock_recovery [i915_bpo]] *ERROR* failed to enable link training [ 158.647999] [drm:intel_dp_start_link_train [i915_bpo]] *ERROR* failed to start channel equalization
Any help would be appreciated. Thanks!