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#1 2022-04-27 01:45:03

From: Kentucky
Registered: 2003-07-07
Posts: 21

[SOLVED] External Video Outputs Not Working on 5.17.4

After updating to 5.17.4 both of the external display connectors (a miniDP and a HDMI) on my laptop stop working.  The laptop display works fine under both.

Machine is a Dell Precision 7540 with dual graphics, a UHD Graphics 630 (i915) and a Radeon PRO WX 3200 (amdgpu). 

5.17.3 - HDMI and DP both work
5.17.4 - HDMI and DP both don't work (I get voltage on the port and the monitor recognizes a connected input, but randr never sees it as an output).

I reverted only the kernel package and have logs of a couple boots with each, the behavior seems consistent.

BOTH configurations give me
[drm:lspcon_init [i915]] *ERROR* Failed to probe lspcon
[drm:intel_dp_detect [i915]] *ERROR* LSPCON init failed on port D
in dmesg during initialization and when I plug a display, as this machine always has, but in .3 and earlier it works anyway.

The only change to the i915 driver I see in the 5.17.4 changelog is tweaks to the version detection for configuring the mmap ioctl, and nothing looks obviously consequential for amdgpu. 

Here is a journal dump for a working 5.17.3 boot and a non-working 5.17.4 boot (with a mile of ignorable KDE-related noise at the end of each).
Other than some variations in timing (especially the expected "Failed to probe lspcon" from i915, and "dce110_edp_wait_for_hpd_ready: wait timed out!" from amdgpu errors), grepping for drm, i915, and amdgpu show identical behavior. 
There are some order variations, but I believe I have examples of both working and non-working boots that happen to bring the cards up in both orders, so it doesn't look like a timing thing.

I'm at a loss for what else to look at, suggestions?

Last edited by PAPPPmAc (2022-04-29 15:32:13)


#2 2022-04-29 15:30:53

From: Kentucky
Registered: 2003-07-07
Posts: 21

Re: [SOLVED] External Video Outputs Not Working on 5.17.4

FIXED: With Early KMS enabled ( eg. MODULES=(i915) in /etc/mkinitcpio.conf) external display connectors work properly on 5.17.4 and 5.17.5.

With my existing configuration it was broken in 5.17.5.  Same behavior as .4.
I was hoping it might have been related to the prime refcount bug but no dice on that.

While I was hunting around in the new log, I noticed that working boots appear to be using fbcon and the non-working boots do not, eg. the working boots log

fbcon: i915drmfb (fb0) is primary device

and the non-working boots are all missing any reference to fbcon. 

On a hunch from seeing no fbcon device, I did the Early KMS thing to see if it would make a difference.  After a reboot with i915 and amdgpu (though I suspect the later is not actually required) in the initramfs, external displays behave properly, and it goes back to loading the i915drmfb fbcon setup. 

It seems like something has changed as of 5.17.4 (or the Arch linux package?) and the video system including i915drmfb doesn't work properly if you late-load the i915 driver.  Easy enough to work around once you know, but I didn't find any obvious reason for that change or warnings about it, Arch-specific or otherwise.

Last edited by PAPPPmAc (2022-04-29 16:00:41)


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