[Bug 86504] New: [BYT/BSW] eDP black screen when backlight is set over update_status path

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86504

            Bug ID: 86504
           Summary: [BYT/BSW] eDP black screen when backlight is set over
                    update_status path
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: rodrigo.vivi at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 109785
  --> https://bugs.freedesktop.org/attachment.cgi?id=109785&action=edit
dmesg

xset dpms force off

leads to a frozen blank screen without any way to recover from it.
It happens that on update_status path backlight is disabled before the regular
path and it causes this issue.

If we avoid "&= ~EDP_BLC_ENABLE;" when coming from backlight_ops.update_status
path everything works correctly as expected.

For a long time I believed that it was a PSR issue, but when fighting against
it I noticed it was happening 100% of the time even with PSR disabled.
So I just reproduced and collected log of it on today's nightly that doesn't
have PSR for VLV merged yet.

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