Single monitor causes kernel panic. Dual works fine.

rolling.robot · 2021-12-04 16:10:05

Hi, all.

I am experiencing a very strange problem: my system won't boot without an external monitor. External monitor can be attached either via my dock station WD-15 (usb-C, not thunderbolt) or via laptop's HDMI port.
When the monitor is connected, everything works good. When I try to boot without external monitor I experience kernel panic (blinking CAPS) shortly after login screen: when gdm is enabled, I can type or move the mouse for a second or so before freeze. Same without graphics (if I do not start display manager). Unfortunately I can see no kernel messages as the screen turns black. Kernel panic also occurs in case I unplug the monitor.

Boot with

nomodeset

kernel parameter does solve freeze, but in this case display manager won't work.
Further I thought that graphics cause the freeze and found many complaints about i915 with dual monitor setting, so I tried to blacklist it with kernel parameter, but no luck, freezes continue in that case.

I have the following settings:
Intel microcode is installed and loaded with initramfs by grub.
Linux: 5.15.5-arch1-1 #1 SMP PREEMPT Thu, 25 Nov 2021 22:09:33 +0000 x86_64 GNU/Linux
VGA compatible controller: Intel Corporation UHD Graphics 620 (rev 07)
HW: Dell Latitude 7390

It is kind of funny that most threads on the internet claim that dual monitor is not working properly, while for me dual is OK, but running a single laptop monitor is an issue.

What other kernel parameters should I try to narrow the problem or solve it?
How can I get more information so that I can file a bug report upstream?

Any help is appreciated.

seth · 2021-12-04 16:30:23

fastboot, psr, fbc, dc, cstate … I guess the second output prevents certain power saving features and one of them kills the system.

https://wiki.archlinux.org/title/Intel_ … sion_crash
https://wiki.archlinux.org/title/Intel_ … nable_fbc)
https://wiki.archlinux.org/title/Intel_ … flickering

If not, we'll require a crash dump of the kernel, https://wiki.archlinux.org/title/Kdump

rolling.robot · 2021-12-04 18:42:16

Hi, seth, thanks for the help.

I have tried the following kernel options:
intel_idle.max_cstate=1 -- no effect
i915.enable_dc=0 -- exit to recovery shell at startup. If I skip this with C-D, I notice no other issues.
ahci.mobile_lpm_policy=1 -- exit to recovery shell and subsequent kernel panic
i915.enable_fbc=1 -- exit to recovery shell and kernel panic
i915.enable_psr=0 -- exit to recovery shell and no other issues if ignored

Two of the options essentially fix the problem for me. It looks like a temporary solution so I think I'll tinker a bit to obtain Kdump in several weeks now...
Still, recovery shell worries me a bit. Can I safely ignore it for now?

seth · 2021-12-04 21:06:36

I'd omit only psr (if this allows stable usage)
About the recovery shell: what error leads up to that? (In doubt check the system journal of the boot, but it should show up before the recovery shell is entered)

Possibly https://wiki.archlinux.org/title/Kernel … _KMS_start ?

rolling.robot · 2021-12-05 08:42:56

Right, I checked diffs between regular boot and the one with the option "i915.enable_dc=0"
The result is that recovery shell was spawning because I overlooked option "single" that was passed by grub menu entry that I modified. Removing this option omits spawning the recovery shell.

Arch Linux

#1 2021-12-04 16:10:05

Single monitor causes kernel panic. Dual works fine.

#2 2021-12-04 16:30:23

Re: Single monitor causes kernel panic. Dual works fine.

#3 2021-12-04 18:42:16

Re: Single monitor causes kernel panic. Dual works fine.

#4 2021-12-04 21:06:36

Re: Single monitor causes kernel panic. Dual works fine.

#5 2021-12-05 08:42:56

Re: Single monitor causes kernel panic. Dual works fine.

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