The regression was caused by this commit:
0e7a2fe Revert "drm/i915: write backlight harder"
The reverted commit (719429a drm/i915: write backlight harder) is known to enable working backlight controls on the XPS 13 and some other models, but apparently causes black-screen or no-backlight-controls after suspend on some other models (per bugzilla report). Discussion of the revert starts about here: https://bugzilla.kernel.org/show_bug.cgi?id=47941#c41
Reference information:
The regression was caused by this commit:
0e7a2fe Revert "drm/i915: write backlight harder"
The reverted commit (719429a drm/i915: write backlight harder) is known to enable working backlight controls on the XPS 13 and some other models, but apparently causes black-screen or no-backlight- controls after suspend on some other models (per bugzilla report). Discussion of the revert starts about here: https:/ /bugzilla. kernel. org/show_ bug.cgi? id=47941# c41