[Bug 101619] New: DPCD backlight causes black screen on ThinkPad X1 Carbon 4th Gen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101619

            Bug ID: 101619
           Summary: DPCD backlight causes black screen on ThinkPad X1
                    Carbon 4th Gen
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: david.weinehall at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 132294
  --> https://bugs.freedesktop.org/attachment.cgi?id=132294&action=edit
dmesg with drm.debug=0xE

With DPCD backlight enabled (default as of a few days ago in drm-tip), the
backlight no longer works properly on my ThinkPad X1 Carbon 4th Gen (2560x1440
display option).

If I pass i915.enable_dpcd_backlight=0 on boot the backlight behaves as it
should (because of this workaround I'm filing the issue as normal rather than
major).

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