[Bug 89661] [ivb] Unable to configure 3rd pipe (e.g. LVDS + DP + DP)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89661

--- Comment #24 from Lars Ivar Igesund <larsivar at igesund.net> ---
I have a Dell XPS 15 laptop with a HD4600 integrated graphics (and an Nvidia
discrete GPU which I normally don't use). I now run Kubuntu 16.04.1, but I had
issues with this also on 14.04.

The laptop screen is 4k, and then there is a HDMI out and a mini DP out. I have
a 4k Philips UltraClear and a Dell 1920x1200. The laptop came with a
DisplayLink docking station which initially made it possible to use these
external screens, but with a bunch of caveats and bugs. After the upgrade to
16.04, it just didn't work anymore.

So both before and after the upgrade, I've tried to use the outputs in the
laptop directly.

Before that upgrade;
The 1920x1200 generally worked over the HDMI, but the 4k didn't. I remember
actually finding this bug report while trying it out, but in the end the
DisplayLink stuff worked well enough for it to not be worth it.

After the upgrade;
Everything actually just worked (although I took the laptop screen down to a
1920x1080), so I had eDP1 + DP1 + HDMI1 all working together, with different
resolutions. This was before the summer. 

Then after the summer I had to disconnect the HDMI monitor (at 1920x1200) as it
messed up the desktop, but presumably that was a bug in plasma.

After that again, the 4k monitor over mini DP has worked, but had occasional
(and quite serious) flickering issues.

Then, two days ago, the 4k monitor decided to no longer want to be part, and
now it seems to be back to the issue seen here, with the same type of errors as
mentioned by Jiri:

failed to set mode: Invalid argument [22]

I did not run upgrade in the days preceding this last change.

Anecdote: Connecting the 1920x1200 screen over HDMI now works flawlessly.

Is there something I can do to help debug/diagnose this?

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