[Intel-gfx] [bug] i915 flickering display after some of the 5.5rc3 patches

[Blaž Hrastnik]

Hi! I'm using a Surface Laptop 3 (Intel version, i7-1065G7) which is running the i915 driver. I have a screen flicker issue in 5.5rc that I wasn't able to track down initially because of the sheer volume of commits to bisect. Luckily, I can reproduce the same issue on 5.4.6 now as well after the latest round of Arch Linux specific patches (upgrading arch1 -> arch3 will produce the bug).

https://git.archlinux.org/linux.git/log/?h=v5.4.6-arch3

- During boot, the screen will flash to black for a second, then back on, two or three times.
- After that, when starting a wayland session the same thing happens (also twice). 
-  If I plug in a power cable, the same thing happens (again twice). It doesn't happen on unplug though.

After the initial flicker, it's completely fine unless I plug a power cable in.

I managed to bisect the issue down to 2-3 patches Kai Vehmanen made regarding intel_audio:

It works on commit "x86/intel: Disable HPET on Intel Ice Lake platforms". But it doesn't work on "drm/i915: extend audio CDCLK>=2*BCLK constraint to more platforms"

So one of these three patches cause it:

- https://patchwork.freedesktop.org/patch/331957/
- https://patchwork.freedesktop.org/patch/334110/
- https://patchwork.freedesktop.org/patch/334111/

(I think it's not 334110, because I initially tested a build with just that commit reverted).

Let me know if you need any specific debug information to diagnose further.

-- Blaž