Displayport daisy chained displays get recognized as the same

[Florian]

Hi,

I'm using Ubuntu 16.04.2 LTS.

Since I upgraded to 4.4.0-77, my daisy chained displays seem to get recognized as the same. Before, I've been using 4.4.0-72. Booting the older Kernel using grub also still works.

I'm using two Dell U2715H Displays daisy chained. (DP1-1 and DP1-8) Both with 2560x1440px. Simultaneously, I use my Notebook Display with 1920x1080px. (eDP1) I have a script, which I run manually after startx, which sets up my environment. It does:

xrandr --output DP1-1 --mode 2560x1440
xrandr --output DP1-8 --mode 2560x1440
xrandr --output DP1-8 --left-of eDP1
xrandr --output DP1-1 --left-of DP1-8

On 4.4.0-77 both, DP1-1 and DP1-8 show the same picture (left-of eDP1);
whereas on 4.4.0-72,
DP1-1 shows the picture left of DP1-8,
and DP1-8 shows the picture left of eDP1
as expected.

If I take a screenshot using xfce4-screenshooter, everything seems fine.

I attached the output from xrandr on both kernels, screenshots from both pictures and reference pictures taken with my camera for you to see what actually happens.

Thanks.

Screen 0: minimum 8 x 8, current 7040 x 1440, maximum 32767 x 32767
eDP1 connected 1920x1080+5120+0 (normal left inverted right x axis y axis) 309mm x 173mm
   1920x1080 60.05*+ 59.93
   1680x1050 59.95 59.88
   1600x1024 60.17
   1400x1050 59.98
   1600x900 60.00
   1280x1024 60.02
   1440x900 59.89
   1280x960 60.00
   1368x768 60.00
   1360x768 59.80 59.96
   1152x864 60.00
   1280x720 60.00
   1024x768 60.00
   1024x576 60.00
   960x540 60.00
   800x600 60.32 56.25
   864x486 60.00
   640x480 59.94
   720x405 60.00
   640x360 60.00
DP1 disconnected (normal left inverted right x axis y axis)
DP1-1 connected 2560x1440+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440 59.95*+
   2048x1152 60.00
   1920x1200 59.88
   1920x1080 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98
   1600x1200 60.00
   1680x1050 59.95
   1280x1024 75.02 60.02
   1200x960 59.99
   1152x864 75.00
   1280x720 60.00 50.00 59.94
   1024x768 75.08 60.00
   800x600 75.00 60.32
   720x576 50.00
   720x480 60.00 59.94
   640x480 75.00 60.00 59.94
   720x400 70.08
DP1-8 connected 2560x1440+2560+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440 59.95*+
   2048x1152 60.00
   1920x1200 59.88
   1920x1080 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98
   1600x1200 60.00
   1680x1050 59.95
   1280x1024 75.02 60.02
   1200x960 59.99
   1152x864 75.00
   1280x720 60.00 50.00 59.94
   1024x768 75.08 60.00
   800x600 75.00 60.32
   720x576 50.00
   720x480 60.00 59.94
   640x480 75.00 60.00 59.94
   720x400 70.08
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-77-generic 4.4.0-77.98
ProcVersionSignature: Ubuntu 4.4.0-77.98-generic 4.4.59
Uname: Linux 4.4.0-77-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: florian 2980 F.... pulseaudio
 /dev/snd/pcmC1D0c: florian 2980 F...m pulseaudio
 /dev/snd/pcmC1D0p: florian 2980 F...m pulseaudio
 /dev/snd/controlC1: florian 2980 F.... pulseaudio
Date: Tue May 9 11:27:40 2017
HibernationDevice: RESUME=/dev/mapper/data-swap
InstallationDate: Installed on 2015-08-01 (646 days ago)
InstallationMedia: Ubuntu-Server 15.04 "Vivid Vervet" - Release amd64 (20150422)
MachineType: Notebook W740SU
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-77-generic.efi.signed root=/dev/mapper/system-system ro
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-77-generic N/A
 linux-backports-modules-4.4.0-77-generic N/A
 linux-firmware 1.157.8
SourcePackage: linux
UpgradeStatus: Upgraded to xenial on 2016-06-12 (330 days ago)
dmi.bios.date: 08/13/2013
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 4.6.5
dmi.board.asset.tag: Tag 12345
dmi.board.name: W740SU
dmi.board.vendor: Notebook
dmi.board.version: Not Applicable
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: Notebook
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr4.6.5:bd08/13/2013:svnNotebook:pnW740SU:pvrNotApplicable:rvnNotebook:rnW740SU:rvrNotApplicable:cvnNotebook:ct9:cvrN/A:
dmi.product.name: W740SU
dmi.product.version: Not Applicable
dmi.sys.vendor: Notebook

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream stable kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.4 stable kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4.68

[Florian (lokokoze)]

I've tested the latest upstream stable kernel. (4.4.68-040468-generic). The bug persists.

[Joseph Salisbury (jsalisbury)]

Thanks for the update. It's probably best for us to perform a bisect to identify the commit that introduced this.

It sounds like 4.4.0-72 did not exhibit the bug. To perform the bisect, we need to identify the last good version and the first bad version. Can you test 4.4.0-75? It can be downloaded from:

https://launchpad.net/~canonical-kernel-team/+archive/ubuntu/ppa/+build/12451435

You would need to install both the linux-image and linux-image-extra .deb packages.

[Florian (lokokoze)]

Now tested 4.4.0-75-generic. The bug is also in this Version.

You could also provide me more than one kernel I should test, if this speeds up finding this bug.

Just a note: Before trying the 4.4.68 kernel, I've tried 4.12-rc1 by accident. The bug does not seem to exist in 4.12-rc1 anymore.

[Joseph Salisbury (jsalisbury)]

Can you test the v4.11 final kernel? If it has the bug, we can "Reverse" bisect between 4.11 and 4.12-rc1 to find the commit that fixes this.

The 4.11 final kernel is available from:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.11/

[Florian (lokokoze)]

Kernel 4.11.0-041100-generic shows another issue: DP1-1 won't show any picture and simply enters standby mode.

Output from xrandr is the same as in my first post.

[Florian (lokokoze)]

I'm sorry, 4.11.0-041100-generic doesn't show the bug. I performed a clean shutdown and reboot to revalidate it, and now 4.11.0-041100-generic works as well as 4.12-rc1.

[Florian (lokokoze)]

I also want to note, that the initial resolution for DP1-1 (after startx, before i run my display script), is quite random. Most of the times it's 1920x1080, which is also the initial resolution for DP1-8. But sometimes it's a smaller (less pixels) resolution.

[Florian (lokokoze)]

4.4.0-81 still contains this bug. Anything new, I should test?

[Florian (lokokoze)]

I've done a dist-upgrade to Ubuntu 17.04 with kernel 4.10.0-26-generic. This kernel doesn't contain the bug.