(In reply to Wolfgang Haupt from comment #0)
> dmesg:
> http://sprunge.us/TKbO

Please ensure the dmesg starts at boot (use log_buf_len=4M or something if needed), and attach dmesg to the bug. Don't reference external sites that are bound to lose the data.

[    3.348528] [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:58:DP-1]
[    3.348534] [drm:intel_dp_detect] [CONNECTOR:58:DP-1]
[    3.348831] [drm:lspcon_wake_native_aux_ch] Native AUX CH up, DPCD version: 1.2
[    3.348847] [drm:lspcon_resume] LSPCON recovering in PCON mode after 0 ms

It's our old friend LSPCON :(

The 4:2:0 support for that is still WIP. You may want to try the patches here:
https://patchwork.freedesktop.org/series/28536/

Assuming you would apply them on top of drm-tip you should only need the last three. Not sure if the entire series would cleanly apply against 4.14-rc.

Created attachment 134412 [details]
dmesg.log

Attached dmesg output beginning at boot.

Created attachment 134441 [details]
dmesg drm-tip + yuv 4:2:0 patches

I built the drm-tip branch and applied the 3 patches.
Now I can choose 4k@60 again.
However when I reboot, BIOS and Bootloader screen turns green.
After transition to user space it seems to go away.
Attached you can find the dmesg output.

I've been testing a few days now and also tried different builds.
For some reason I always have a black screen flickering like with kernel 4.13 now and can't really figure out why this happens.

I tried to diff the dmesg output and miss the line that states "YCbCr 4:2:0".
Also the screen does not turn green anymore when in bios and bootloader state.
But I see the debug outputs of the yuv 4:2:0 patches.
Current dmesg.log attached.
Any thoughts?

Created attachment 134557 [details]
dmesg after some testing

I kept testing a little bit and built the drm-tip branch occasionally.
While I now always have 3180x2160_60Hz available there's one major issue, namely black screen flickering.
Additionally I'm very interested in yuv 4:2:0 support.

How can we proceed?
The bug title has nothing to do with the mentioned problem nor with yuv 4:2:0.
Shall I close this one and open a dedicated one for the black screen flickering issue?

(In reply to Wolfgang Haupt from comment #7)
> I kept testing a little bit and built the drm-tip branch occasionally.
> While I now always have 3180x2160_60Hz available there's one major issue,
> namely black screen flickering.
> Additionally I'm very interested in yuv 4:2:0 support.
> 
> How can we proceed?
> The bug title has nothing to do with the mentioned problem nor with yuv
> 4:2:0.
> Shall I close this one and open a dedicated one for the black screen
> flickering issue?
Hello Wolfgang,
This bug should be closed once the patches are merged upstream. For the other issues the best will be to open a dedicated one, as you mentioned before.

Hi, any news on this? Thank you.

First of all. Sorry about spam.
This is mass update for our bugs. 

Sorry if you feel this annoying but with this trying to understand if bug still valid or not.
If bug investigation still in progress, please ignore this and I apologize!

If you think this is not anymore valid, please comment to the bug that can be closed.
If you haven't tested with our latest pre-upstream tree(drm-tip), can you do that also to see if issue is valid there still and if you cannot see issue there, please comment to the bug.

Closing, please re-open if still occurs.