Netbook display is turned off on login screen on startup

[Leonardo Soares Müller]

On the netbook model Positivo Mobo 5800, it was noticed that, on the end of the boot process, the LightDM greeter won't appear and the screen will turn off, disabling the backlight too. To be able to log in to the graphical interface, it's required to go to a tty (for example, tty1) and then back to the LightDM greeter (which is tty7 on this case).

When going back to the tty7, it's noticed that there are text still from the boot for a few seconds, until the greeter finally appears.

The CPU is an Intel(R) Atom(TM) CPU N2600 @ 1.60GHz, it has a gma500 GPU. While gma500 is limiting, I've not observed this LightDM bug with, for example, the Positivo Mobo 5900, which has the same CPU and same GPU with the same revision and, even when applying the same image to both, the 5900 works while the 5800 fails.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: lightdm 1.30.0-0ubuntu4~20.04.2
ProcVersionSignature: Ubuntu 5.4.0-100.113-generic 5.4.166
Uname: Linux 5.4.0-100-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.21
Architecture: amd64
CasperMD5CheckResult: skip
Date: Thu Feb 17 15:30:44 2022
ProcEnviron:
 LANGUAGE=pt_BR:pt:en
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=pt_BR.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)