This problem affects only the new 1080p model of XPS13.
It was introduced in 3.8.0-18.28 by this fix for another regression, LP: #1162026:
[ Kamal Mostafa ]
* SAUCE: (no-up) drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13 backlight - LP: #1162026, #1163720
This problem affects only the new 1080p model of XPS13.
It was introduced in 3.8.0-18.28 by this fix for another regression, LP: #1162026:
[ Kamal Mostafa ]
* SAUCE: (no-up) drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13
backlight
- LP: #1162026, #1163720