i915 [drm] *ERROR* CPU pipe A FIFO underrun: cannot boot and display goes bonkers
System
Hardware: Dell XPS 15 9575 2-in-1 with Intel UHD 630 iGPU and AMD Vega M dGPU
Kernel: 5.16.2
Linux: Manjaro Linux x86_64
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 630 (rev 04)
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Polaris 22 XL [Radeon RX Vega M GL] (rev c0)
Symptoms: on first reboot after upgrade to 5.14.2, after a few (normal) boot messages display flickers with graphical glitches all over the place (mostly blank screen, blueish lines sweeping from the top of the screen).
Details
Ruled out plymouth, gdm and sway: same issue with those removed and booting to a tty. Ruled out a hardware failure: Ubuntu live USB boots fine. Both GPUs are usable.
Boot to tty is possible when using i915.modeset=0 (or nomodeset) but then no DRM is available and I cannot run sway.
The only relevant thing I noticed is the following kernel message (not present with 5.13):
i915 0000:00:02.0: [drm] *ERROR* CPU pipe A FIFO underrun
Attaching the output of lspci -vvnn and a full journalctl dump for the kernel in a failing boot. journalctl-kern.log lspci-vvnn.txt
Not sure which other details are relevant, feel free to ask for more.
This is how the crazy flickering looks like:
Others having this bug: