Bug#925908: buster fails to boot as far as lightdm greeter on N3050

[Phil Morrell <debian@emorrp1.name>]

Control: severity -1 critical
Control: tags -1 upstream patch

Source: linux
Followup-For: Bug #925908
Justification: breaks the whole system

Please backport [9fa246256] to buster, see [xserver summary] for
details. The symptom is booting to a blank VT7 with the cursor not
flashing, other virtual consoles work fine, nomodeset does not help.

Bumped severity because there's no end-user workaround and does not
complete the full boot process. I have downgraded from snapshot:

echo 'deb [check-valid-until=no] https://snapshot.debian.org/archive/debian/20190326T095837Z/ buster main' \
	| sudo tee /etc/apt/sources.list.d/snapshot.list
sudo apt update
sudo apt install linux-image-amd64=4.19+102

I've included some debug messages from various logs that were misleading
because debian bugs seem to be well indexed by search engines.

[9fa246256]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9fa246256e09dc30820524401cdbeeaadee94025
[xserver summary]: https://gitlab.freedesktop.org/xorg/xserver/issues/542#note_164738
--
Phil Morrell (emorrp1)



lspci/lscpu
00:02.0 VGA compatible controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Integrated Graphics Controller (rev 21)
Model name:          Intel(R) Celeron(R) CPU  N3050  @ 1.60GHz

.local/share/xorg/Xorg.1.log after sudo startx:
[  1308.631] (EE) modeset(0): failed to set mode: Invalid argument
[  1308.632] (EE) 
Fatal server error:
[  1308.632] (EE) EnterVT failed for screen 0
[  1308.632] (EE) 
[  1308.632] (EE) 
Please consult the The X.Org Foundation support 
         at http://wiki.x.org
 for help. 
[  1308.633] (EE) Please also check the log file at "/home/emorrp1/.local/share/xorg/Xorg.1.log" for additional information.

/var/log/lightdm/seat0-greeter.log
** (lightdm-gtk-greeter:11572): WARNING **: [PIDs] Failed to execute command: upstart

lightdm.service starts successfully



-- System Information:
Debian Release: 10.0
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-5-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled