Comment 18 for bug 1712508

I confirm this bug is present on Ubuntu 18.04, my hardware is an Intel HD Graphics 5500.

It was working fine on the previous LTS, 16.04; if I use kernel 4.4.0-161-generic from Ubuntu 16 Xenial I can boot Ubuntu 18 Bionic fine, thus I conclude it's something in the kernel.

I have tried these options (individually) without any effect: i915.enable_ips=0 swiotlb=force i915.enable_ips=0 intel_idle.max_cstate=1 i915.enable_rc6=0 i915.enable_psr=0

On the good kernel I see this error in dmesg:
[drm:intel_dp_link_training_channel_equalization [i915]] *ERROR* failed to train DP, aborting

While on the bad one there are no such failures as it detects everything:
[ 10.429894] input: HDA Intel HDMI HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:03.0/sound/card0/input22
[ 10.429989] input: HDA Intel HDMI HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:03.0/sound/card0/input23
[ 10.430070] input: HDA Intel HDMI HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:03.0/sound/card0/input24
[ 10.430166] input: HDA Intel HDMI HDMI/DP,pcm=9 as /devices/pci0000:00/0000:00:03.0/sound/card0/input25
[ 10.430250] input: HDA Intel HDMI HDMI/DP,pcm=10 as /devices/pci0000:00/0000:00:03.0/sound/card0/input26

The most interesting clue to find a solution is however to be found in gparted-live-1.0.0-5-amd64.iso: when booting this live distro via USB I get exactly the same flickering (it uses kernel 5.2.0) but when starting Xorg the problem disappears. Switching back to any VT shows the flickering problem.

I was wondering if it could be possible to dissect the GParted live ISO to find out what makes it work when starting Xorg.