lightdm should do modesetting on startup

[Maxim Mikityanskiy]

When lightdm launches Xorg, it should do some video mode setting rather than just inheriting current video mode. There are some situations where it is needed:

1. I use lightdm with light-locker. I have no fbcon kernel module loaded. When screensaver activates, screen turns off. Then light-locker switches to greeter, new Xorg starts, but screen was turned off by screensaver, so new Xorg will inherit current video mode and come up with no screens enabled. The greeter starts up, but I can only enter my password blindly. This is a major blocker.

2. BIOS or bootloader set some video mode, then i915 kernel module loads with i915.fastboot=1. It preserves that video mode. Then lightdm starts and launches Xorg. Xorg video driver preserves current video mode. Then lightdm should do some initial modesetting, possibly setup monitors etc.

Lightdm is a good place to do initial modesetting as it can remember user settings, and it's the first application user interacts with, so native screen resolution should be already set.

Lightdm must at least check that some video output is enabled, or we can end up with situation 1.

P.S. NOTABUG in Xorg driver: https://bugs.freedesktop.org/show_bug.cgi?id=88960 (there are steps to reproduce and some explanations from Xorg developer).

[Robert Ancell (robert-ancell)]

Shouldn't this be handled by the greeter / session? LightDM just starts the X servers then the first thing the sessions do is configure X the way they like it. The LightDM daemon really has no idea what settings to apply.

[Maxim Mikityanskiy (maxtram95)]

Maybe the greeter should configure screens. Greeter will be able to configure screens as he likes and use them as he wants, it's good. But the same code to configure screens will be included in all greeters, that's not very good. Anyway, some component of DM have to do this job, or the user will end up with no screen at all.

Temporary workaround (not a real solution to the problem): in /etc/lightdm/lightdm.conf:

[SeatDefaults]
display-setup-script=/usr/bin/xrandr --auto