Display Adapter Chain, Cable Disconnect causes Nouveau trace

Submitted by mbazzinotti@gmail.com

Assigned to Nouveau Project

Link to original bug (#104344)

Description

Created attachment 136308
collation of syslog grep'd for "nouveau|drm"; includes trace. there was no pertinent log info right before the trace occurred.

While experimenting with physical connections to avert Flicker Bug 88272
(https://bugs.freedesktop.org/show_bug.cgi?id=88272)

I found myself using a mini DisplayPort(mDP) adapter which has 3 outputs
(HDMI, DVI, and DP), with its DP output connected to a second DP->DVI adapter.

Let's call the first adapter A, and the 2nd adapter B. The connections are:


------- mDP --- DP --- DVI ---------
Laptop |-----| A |----| B |---| Monitor |
------- --- --- ---------


While connected, display appeared "normal" as per Bug 88272 screen flicker. When
I unplugged the DVI cable from adapter B, this trace appeared in the dmesg attachment. Dmesg Output before the trace was not relevant. This issue can be reproduced again and again by reconnecting and disconnecting the cable.

This does not crash X. The desktop appears to run just fine, even during the nouveau crash IIRC. If I was not watching dmesg, I may not have even noticed.

The problem does not happen if unplugging the root adapter from the laptop. I have not tried unplugging the 2nd adapter to see what happens in that case.

Note: When adapter A is plugged via DVI to monitor directly, unplugging the DVI cable does not cause a crash; no call stack is outputted to dmesg in this case.

---------
Hardware |
---------
Macbook Pro 5,4 15" mid-2009
Nvidia GeForce 9400m
mini DisplayPort -> "Gigaware" DVI/HDMI/Displayport adapter -> HP DP>DVI
adapter
Dell LCD Monitor model E2011Hc

--------
Software|
--------
Gentoo Linux 4.12.12.
x11-base/xorg-server-1.19.5
x11-drivers/xf86-video-nouveau-1.0.15
i3wm
No compositor

kernel command line: ro root=PARTUUID=xxxxxxxx net.ifnames=0

-----

Attachment 136308, "collation of syslog grep'd for "nouveau|drm"; includes trace. there was no pertinent log info right before the trace occurred.":
syslog-nouveau-drm-trace.txt