Flickering single display in multi-head XRandR setup

Andreas Mohr andi at lisas.de
Fri Mar 25 09:22:41 UTC 2016

On Thu, Mar 24, 2016 at 11:18:01AM +0000, xorg-request at lists.x.org wrote:
> Date: Thu, 24 Mar 2016 12:12:34 +0100
> From: martin f krafft <madduck at madduck.net>
> There is something very weird going on, which you may witness in the
> video downloadable here:
> http://scratch.madduck.net/xorg-display-flicker.mp4 (8Mb)
> The left-most display (DP0) keeps turning off and on (or resets
> itself), and generally, it flickers and the pixels jiggle around.
> The other two displays are perfectly fine. The monitor on DP1 is of
> exactly the same make as that on DP0.

While it wasn't explicitly written,
let me just assume that you did try
actively connector/cable-swapping those "exactly the same make" monitors,
with identical results.

> Do you have any idea what might be going on? Why would the left-most
> display of three, all connected to the same card, act up, while the
> other two are just fine and stable?

Perhaps unthinkable, but the connectors of the card
might be implemented / wired up asymmetrically,
e.g. due to an ickily varying length of traces, or EMI issues.

(more esoteric option:) Try swapping plug (thus, wires) of power cord -
there are cases known
where having the live wire of the cord be the *other* one
will avoid/reduce EMI issues.

Another idea might be relocating completely
i.e. re-constructing the whole test set
at a sufficiently/entirely different location,
to see whether there is a weird location dependence.

So, I guess the actions I mentioned
mainly serve to figure out the separation of
whether it is a setup-/environment-related weirdness, or
whether it is a driver implementation/configuration issue in fact.


Andreas Mohr

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