Dell XPS 15 9575: Flickering white/black screen once KMS comes up in 5.14 through 5.18
Downstream bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1958620
In released kernels since 5.14, the display is blank/flickering once DRM drivers are loaded/KMS kicks in if booted without an external display plugged in. Booting with an external display, or plugging in an external display fixes the issue.
A bisection shows the commit that broke things was: 6d7a793aabf31d7ba2b16fc13a94ccf0b90e4be0: drm/i915/display: Allow fastsets when DP_SDP_VSC infoframe do not match with PSR enabled
On drm-tip, the bug is fixed as of commit: 5ac860cc52540df8bca27e0bb25b6744df67e8f0: drm/i915: Fix DBUF bandwidth vs. cdclk handling
However, that commit doesn't cleanly apply to eg the 5.15 kernel that ubuntu wants to ship in its next release.
- what is the best path toward fixing it in 5.15/other stable releases?
- are there any things that should be done to make sure it doesn't break again?
Thanks!