[Bug 1759950] Re: Lid-close suspend: blank screen when switching to user session

[TJ]

I've captured a log where it doesn't fail. The difference is a single
error message. In failing sessions there is an additional "Failed to
configure CRTC..." which is not seen here:

xfce4-settings(displays): UPower lid event received (closed -> open).
xfce4-settings(displays): Toggling internal output LVDS.
xfce4-settings(displays): CRTC 79 assigned to LVDS.
xfce4-settings(displays): CRTC 79, output list[0] -> 82.
xfce4-settings(displays): LVDS will be re-enabled.
xfce4-settings(displays): Normalized CRTC 79: size=1280x800, pos=0x0.
xfce4-settings(displays): min_h = 200, min_w = 320, max_h = 4096, max_w = 4096, prev_h = 800, prev_w = 1280, prev_hmm = 211, prev_wmm = 338, h = 0, w = 0, hmm = 0, wmm = 0.
xfce4-settings(displays): Configuring CRTC 79.
xfce4-settings(displays): Applying changes to CRTC 79.
xfce4-settings(displays): Applying CRTC 79 Transform: x=0.000000 y=0.000000, filter=bilinear.
xfce4-settings(displays): Configuring CRTC 80.

(xfsettingsd:7482): xfsettingsd-CRITICAL **: 14:49:59.549: Failed to
apply display settings

xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 79.
xfce4-settings(displays): Detected CRTC 80.
xfce4-settings(displays): Detected output 82 LVDS.
xfce4-settings(displays): Noutput: before = 1, after = 1.

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Title:
  Lid-close suspend: blank screen when switching to user session

Status in Light-Locker:
  New
Status in Xfce4 Power Manager:
  Confirmed
Status in light-locker package in Ubuntu:
  Incomplete
Status in systemd package in Ubuntu:
  New
Status in xfce4-power-manager package in Ubuntu:
  Confirmed
Status in xfce4-settings package in Ubuntu:
  New
Status in xubuntu-default-settings package in Ubuntu:
  New

Bug description:
  I'm currently testing Xubuntu 18.04 after a do-release-upgrade from
  16.04.

  I discovered a very weird issue. When doing S3 sleep via closing the
  lid, on resume the lock screen appears, I authenticate, but as soon as
  it switches to the user session the screen goes blank - not even a
  backlight.

  Switching to other ttys works and they display correctly but the GUI
  user session remains blank.

  If the system is manually suspended (not using the lid), then resumed
  either by opening the lid or pressing the power button, the GUI user
  session is fine.

  I narrowed it down to xfce4-power-manager and discovered disabling the
  lock-screen cured the issue.

  I cloned the repository and reviewed commits between 1.7 and 1.8.
  Fortunately there aren't many. Looking at 6365683 "Proper exit status
  for light-locker-command" I suspected the change in the SetActive
  return value, and reverted it.

  After a build/install cycle I've found the system now behaves
  correctly so I think the change should be reverted.

  I've created an issue upstream for this at

  https://github.com/the-cavalry/light-locker/issues/108

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