A new issue appeared in Xorg 1.20.1, which I suspect is related to https://bugs.freedesktop.org/show_bug.cgi?id=106715
On a lenovo yoga 1st or 3rd gen (skylake or kabylake), both using the modesetting driver, when resuming from S3 sleep (by closing the lid) or when the monitor goes off with dpms, sometimes the backlight is turned on, but the screen stays completely black.
I verified the issue with kernels 4.17 to 4.19-rc4.
I can "fix" the issue by triggering a display rotation by 90 degrees, which shows the image instantly, and rotating it back (thus my link to the previous bug).
Doing a 180 degree rotation is not sufficient.
I cannot trigger the same problem by running "xset dpms force standby/off".
There's no error or informational message being written to dmesg or Xorg.log.
The behavior is the same if one or two screens are attached (built-in display + external or built-in only).