[Bug 88960] X server comes up with black screen if screensaver is activated on another X server

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=88960

--- Comment #8 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to Maxim Mikityanskiy from comment #7)
> (In reply to Chris Wilson from comment #6)
> > (In reply to Maxim Mikityanskiy from comment #5) 
> > > As lightdm relies on that fbcon will turn on the screen before Xorg starts,
> > > and lightdm can come up with no outputs enabled, I will report this bug to
> > > lightdm.
> > 
> > That's actually a bug. The goal is for the kernel to do nothing and preserve
> > the output configuration from the BIOS. (So whatever configuration is setup
> > in hardware, or in device files, is preserved right up until the user
> > applies their preferences). So that means that even without fbcon, we should
> > basically continue to show the BIOS screen until the splashscreen loads or
> > until the DE fires up (i.e. no flicker boot). The full BIOS preservation is
> > still hidden behind i915.fastboot=1.
> 
> In my situation, when I boot without fbcon and without i915.fastboot=1, BIOS
> leaves me text mode 80×25, then i915 module sets 1024×600 resolution on
> boot, then lightdm starts up with native resolution. The problem only shows
> up when I turn off the screen in first X session and start second lightdm
> greeter. Lightdm doesn't reenable the screen. Really, it should do some
> modesetting to avoid such situations (and to set initial video mode on first
> start if it is needed).

On VT switch, I have to remove the frontbuffer from the CRTC so that the second
VT cannot snoop on the original contents. This is done by removing the primary
plane, but it is supposed to leave the mode intact. So only if the CRTC are off
before we VT switch should we lose the mode information between VT.

Once you lose that information, how do we tell that apart from when the user
intended for the screens to be off until he sets them? We always want to push
the policy as close to the end user as possible, and the default of leaving
things as we find them should result in fewer conflicts.

> What abount i915.fastboot... I tried booting without fbcon and with
> i915.fastboot=1. When lightdm started, my screen's resolution was 640×480,
> but lightdm thought it was 1024×600, so I could see top left corner of the
> picture. When I tried to move mouse to right edge of screen, screen started
> flickering. It stopped flickering when I returned my mouse back. Even
> "xrandr --auto" and "xrandr --output LVDS1 --mode 1024x600" didn't switch to
> 1024×600, "xrandr --current" thought it was current resolution. Something is
> broken with i915.fastboot... should it be reported to the kernel bugtracker?

Yeah, if the BIOS was in VGA text mode, we should just have taken over
completely and set a native mode (if actually setting anything).

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