Bug 108520

Summary: [GK104] MST DisplayPort HiDPI screen flicker
Product: xorg Reporter: JM9 <jhnmlkvch9>
Component: Driver/nouveauAssignee: Nouveau Project <nouveau>
Status: NEW --- QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium    
Version: unspecified   
Hardware: Other   
OS: All   
Whiteboard:
i915 platform: i915 features:
Attachments:
Description Flags
dmesg
none
xorg log none

Description JM9 2018-10-22 23:19:03 UTC
HiDPI MST monitor connected via DisplayPort has bad screen flicker (one to three high speed flickers every 20 seconds or so).

Version of X: 1.20
Nouveau: 1.0.15-3
Kernel: 4.18.16-arch1-1-ARCH

Curiously, the flicker only happens on my Optimus laptop with Hybrid Graphics disabled (Intel off, Nouveau on). The flicker disappears if Hybrid Graphics is enabled (Both Intel and Nouveau cards on).

Can't find anything relevant in dmesg, journal etc., but let me know which logs will be useful and I can upload them.
Comment 1 Ilia Mirkin 2018-10-23 00:09:02 UTC
I'd guess that in hybrid mode, the DP port is driven by Intel, which has a more battle-tested implementation.

dmesg and xorg log will be useful to provide background information, even if they don't have any errors in them.
Comment 2 JM9 2018-10-23 18:56:52 UTC
Created attachment 142160 [details]
dmesg
Comment 3 JM9 2018-10-23 18:57:17 UTC
Created attachment 142161 [details]
xorg log
Comment 4 JM9 2018-10-23 18:57:39 UTC
(In reply to Ilia Mirkin from comment #1)
> I'd guess that in hybrid mode, the DP port is driven by Intel, which has a
> more battle-tested implementation.
> 
> dmesg and xorg log will be useful to provide background information, even if
> they don't have any errors in them.

attached xorg log and dmesg
Comment 5 Ilia Mirkin 2018-10-23 19:04:18 UTC
OK, so ...

A few facts:

 - GK104
 - Driving 4 monitors

Question: Are the 2560x1440 and 1920x1200 daisy-chained (hence the "MST" reference), or is it just that the 2560x1440 monitor's manufacturer name is "MST", without any reference to Multi-Stream Transport?
Comment 6 JM9 2018-10-23 19:38:59 UTC
(In reply to Ilia Mirkin from comment #5)
> OK, so ...
> 
> A few facts:
> 
>  - GK104
>  - Driving 4 monitors
> 
> Question: Are the 2560x1440 and 1920x1200 daisy-chained (hence the "MST"
> reference), or is it just that the 2560x1440 monitor's manufacturer name is
> "MST", without any reference to Multi-Stream Transport?

They are not daisy-chained. I'm not sure about the MST reference. I think this is  a regression in X11 1.20. I filed a separate bug about that:
https://bugzilla.freedesktop.org/show_bug.cgi?id=108516
(If Hybrid Graphics is enabled, MST reference is gone.)

Another odd thing I noticed is, if I start X and then hot plug the monitor, there is no flicker.
Comment 7 JM9 2018-10-23 20:29:42 UTC
(In reply to JM9 from comment #6)
> (In reply to Ilia Mirkin from comment #5)
> > OK, so ...
> > 
> > A few facts:
> > 
> >  - GK104
> >  - Driving 4 monitors
> > 
> > Question: Are the 2560x1440 and 1920x1200 daisy-chained (hence the "MST"
> > reference), or is it just that the 2560x1440 monitor's manufacturer name is
> > "MST", without any reference to Multi-Stream Transport?
> 
> They are not daisy-chained. I'm not sure about the MST reference. I think
> this is  a regression in X11 1.20. I filed a separate bug about that:
> https://bugzilla.freedesktop.org/show_bug.cgi?id=108516
> (If Hybrid Graphics is enabled, MST reference is gone.)
> 

Scratch that. I was being confused. The MST reference is still there, but the naming scheme is different.

> Another odd thing I noticed is, if I start X and then hot plug the monitor,
> there is no flicker.
Comment 8 Ilia Mirkin 2018-10-23 20:47:20 UTC
So it sounds like there's a DP ports are hard-attached to the NVIDIA chip, which is why you're seeing it as "DP-1-1" for the "optimus" case. It's actually using the outputs attached to the NVIDIA gpu. The "local" DP outputs are probably meant for a dock.

Are both the 2560x1440 and 1920x1200 monitors attached via DP? Or are there converters in between?
Comment 9 JM9 2018-10-23 21:48:32 UTC
(In reply to Ilia Mirkin from comment #8)
> So it sounds like there's a DP ports are hard-attached to the NVIDIA chip,
> which is why you're seeing it as "DP-1-1" for the "optimus" case. It's
> actually using the outputs attached to the NVIDIA gpu. The "local" DP
> outputs are probably meant for a dock.
> 
> Are both the 2560x1440 and 1920x1200 monitors attached via DP? Or are there
> converters in between?

They are both connected via dock. 2560x1440 (the only one with the flicker problem) is additionally going through a DP to DVI Dual Link Adapter.

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