[Bug 104934] Sometimes does not detect 60Hz Full HD mode for external display, switching to 60 Hz with interlace

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104934

--- Comment #3 from Martin Steigerwald <Martin at Lichtvoll.de> ---
(In reply to Jani Saarinen from comment #2)
> 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.

As of 4.16-rc6 this bug is still valid.

I found a work-around. When I move the DisplayPort cable from DP2 to DP3 or
wise versa *while* the session is running, the 60 Hz resolution is always
detected and I can activate it again.

What can also happen that one Plasma session gets is right and when I open up
another Plasma session via SDDM in the other one only the interlaced mode is
detected. So the one session has the 60 Hz resolution, while the other just has
the interlaced one, yet still with the same cable and at the same time (minus
delay for switching between sessions via Ctrl-Alt-F7/8).

I tried with four cables already. However, I have a cable where this appeared
more rarely (no scientific measurement, just personal impression). Curiously it
was the longest one with 5 meters. So I ordered another cable like this, but
just 2 meters and will test it as well. Since for a long time with previous
kernels I did not see this issue and since the issue always goes away when
moving the Displayport cable between DP2 and DP3, I still think that it is not
or at least not solely a cabling issue.

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