[Bug 110863] Blank screen after locking and vt-switch

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110863

Tomas Janousek <tomi at nomi.cz> changed:

           What    |Removed                     |Added
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                 CC|                            |tomi at nomi.cz

--- Comment #19 from Tomas Janousek <tomi at nomi.cz> ---
I can reproduce this just by doing "xset dpms force off", but not always.

First and foremost, the X server needs to be in a "weird" state. I don't know
how to get into that state, but using my laptop for a few days (suspends,
resumes, docking with two external monitors, undocking, etc.) always eventually
gets it there. If I now switch to another virtual console and "startx", I can't
reproduce it there, but if I logout again and switch back to the "weird" X
that's been running for a few days, it's reproducible just fine. (Which makes
me think this is an xorg-server issue, possibly modesetting driver, not
kernel/drm.)

Anyway, let's assume I'm in this "weird" X server:

If neither compton (nor any other compositor) nor xss-lock (nor xscreensaver
nor anything similar) is running, "xset dpms force off" makes the screen black
(and turns off display backlight, as it should), and no amount of mouse
movements and/or key presses brings it back on. VT switch helps. (BUT, if there
was fullscreen glxgears or mpv, mouse/keys does bring the screen back on. Move
it one pixel off, it won't, but if the GL app is exactly fullscreen, it works.)

If compton is running, but the entire screen is occupied by a single window and
therefore unredirected, it's the same as above: if it's a GL app, screen comes
back on, if it's something boring like urxvt or xscreensaver or xsecurelock, it
doesn't.

If compton is running and there are multiple windows on the screen, everything
works fine, screen comes back up after moving the mouse. That's expected at
this point as compton is kind of like a fullscreen GL thing, right?

If xss-lock is running and the screen is locked, regardless of whether compton
is there or not (it'd have unredirected it anyway), "xset dpms force off" does
make the screen black, but the display backlight stays on. (This seems
unrelated, but it doesn't happen in a fresh non-weird X, so I'm attributing it
to this weirdness as well.) If the screen is not locked, "xset dpms force off"
locks it and displays the screen saver. In non-weird X, even unlocked "… off"
results in black screen with no backlight.

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