Linux 5.10.0-1024.25 breaks HDMI with Intel i915

[Francois Thirioux]

Hi,

[Thinkpad T480s, Intel iGPU 8550u, Ubuntu Focal up-to-date, GNOME Wayland session]

Previous 5.10.0-1023.24 was ok. Kernel 5.8 HWE is ok. I did not test a X session.

Plugging HDMI after GNOME is loaded fails to display anything on the HDMI display.
Plugging HDMI at boot or at GDM screen makes the HDMI display works as usual.

Unplugging HDMI (display only on this one) during GNOME session does not update displays state. Nothing happens. I have to press the switch-display-key on my laptop to actualize the setup and make my laptop's display active.

When I unplug HDMI during GNOME session, nothing appears in logs.

My laptop fails to enter sleep after having unplugged the HDMI.

Related: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1924238

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1926597

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Kai-Heng Feng (kaihengfeng)]

Please test latest drm-tip kernel to make sure the bug is not present in upstream:
https://kernel.ubuntu.com/~kernel-ppa/mainline/drm-tip/current/

[Francois Thirioux (fthx)]

I cannot install this 5.12 kernel because dependencies issue against libc6 (>2.33 needed).

[Kai-Heng Feng (kaihengfeng)]

Please test this kernel:
https://people.canonical.com/~khfeng/lp1926597/

"drm/i915/display: Handle lane polarity for DDI port" is reverted.

[Francois Thirioux (fthx)]

This one did not fix the issue.

(Booting again with 5.8 hwe kernel, I can still confirm that there is no issue, as 5.10 < *-1024.)

[Kai-Heng Feng (kaihengfeng)]

Ok. That means it's regressed by other commits.

Do you know how to compile a kernel? If so, please try the following repo with drm-tip branch:
git://anongit.freedesktop.org/drm/drm-tip

[Francois Thirioux (fthx)]

Unfortunately, I never compiled any kernel and don't know how to do it.

There's one thing I don't understand here: why hdmi does work in gnome after having connected it *before* login in gdm?

[Francois Thirioux (fthx)]

Additionally:

1) boot without hdmi plugged
2) login to gnome session
3) plug in hdmi, nothing happens (but my monitor seems to detect something few seconds but stays black)
4) enter laptop sleep
5) resume from sleep
6) hdmi monitor works as intended

[Kai-Heng Feng (kaihengfeng)]

Some instructions here:
https://wiki.ubuntu.com/KernelTeam/GitKernelBuild

[Francois Thirioux (fthx)]

I don't have the time to compile kernels, at the moment.
But I tried latest CKT hwe kernel:
Linux 5.11.0-16-generic #17~20.04.5-Ubuntu SMP Tue Apr 27 07:37:47 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

And hdmi is working like a charm.

[Francois Thirioux (fthx)]

FYI I still do experience this bug with latest 1030 kernel oem.
No issue running 5.8 hwe or 5.11 hwe.

[Kai-Heng Feng (kaihengfeng)]

Thanks for the update. I think using the HWE kernel is the best compromise for the interim.

[Francois Thirioux (fthx)]

(Yes!)
I now do use a Debian 11 system:
Linux fthx 5.10.0-7-amd64 #1 SMP Debian 5.10.40-1 (2021-05-28) x86_64 GNU/Linux
and hdmi works as intended, FYI.

[Launchpad Janitor (janitor)]

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